Methods of Analysis by the U.S. Geological Survey

National Water Quality Laboratory—Determination of 

Moderate-Use Pesticides and Selected Degradates in 

Water by C-18 Solid-Phase Extraction and Gas 

Chromatography/Mass Spectrometry

Water-Resources Investigations Report 01-4098 

 

U.S. Department of the Interior 

U.S. Geological Survey
Methods of Analysis by the U.S. Geological Survey

National Water Quality Laboratory—Determination of 

Moderate-Use Pesticides and Selected Degradates in 

Water by C-18 Solid-Phase Extraction and Gas 

Chromatography/Mass Spectrometry

By Mark W. Sandstrom, Max E. Stroppel, William T. Foreman, 

and Michael P. Schroeder 

_______________________________________________________

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01-4098 

U.S. Geological Survey Method O-2002-01 

Laboratory Methods (Schedules) 2002 and 2011 

Denver, Colorado 

2001
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

The use of trade, product, or firm names in this report is for descriptive 

purposes only and does not imply endorsement by the U.S. Government. 

For additional information write to: Copies of this report can be purchased from: 

Chief, National Water Quality Laboratory U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

Box 25046, Mail Stop 407 Box 25286 

Federal Center Federal Center

Denver, CO 80225-0046 Denver, CO 80225-0286 
CONTENTS 

Abstract 1 

Introduction 1 

Initial method development 3 

Analytical method 6 

1. Scope and application 6 

2. Summary of method 13 

3. Interferences 14 

4. Apparatus and instrumentation 14 

5. Reagents and consumable materials 16 

6. Sampling methods, sample-collection equipment, and 

 cleaning procedures 16 

7. Standards 18 

8. Gas chromatograph/mass spectrometer performance 19 

9. Calibration 22 

10. Procedure 23 

11. Calculation of results 29 

12. Reporting of results 31 

Final method validation 32 

Other considerations 61 

Conclusions 63 

References cited 63 

Supplement A—Automated solid-phase extraction procedure using 

AutoTrace workstation 65 

Supplement B—Instructions for on-site processing using solid-phase 

extraction (SPE) 67 

FIGURES 

1. Selected ion chromatogram of pesticides and degradates in a 

0.625-nanogram-per-microliter (ng/μL) standard 21 

2. Bias and variability data from reagent-water-set samples 

fortified with analytes at low (0.1 microgram per liter) concentrations and 

prepared during March through December, 1999 60 

TABLES 

1. Analytes that were initially considered or tested but subsequently

eliminated from complete validation experiments because of

problems with ordering, analysis, or recovery 4 

2. Pesticides and degradates included in new method 8 

3. Relation of pesticide degradates included in new method to parent 

pesticides in U.S. Geological Survey methods 2001, 2050, and 2002 11 

4. Volumes of primary combined fortification, internal, and surrogate 

standards needed to prepare suggested concentrations of calibration standards 20 

Contents iii
5. Retention time, quantitation ion, and confirmation ions for analytes, 

surrogates, and internal standards, and selected ion-monitoring group 

and internal standard for analytes and surrogates 24 

6. Bias and variability data from eight reagent-water samples fortified 

with parent pesticide analytes at high (1.0 microgram per liter) 

and low (0.1 microgram per liter) concentrations 33 

7. Bias and variability data from eight reagent-water samples fortified 

with degradates at high (1.0 microgram per liter) and low 

(0.1 microgram per liter) concentrations 36 

8. Bias and variability data from eight surface-water samples fortified 

with parent pesticides and degradates at high (1.0 microgram per liter) 

and low (0.1 microgram per liter) concentrations 38 

9. Bias and variability data from eight ground-water samples fortified 

with parent pesticides and degradates at high (1.0 microgram per liter) 

and low (0.1 microgram per liter) concentrations 41 

10. Method detection limits and preliminary laboratory reporting levels 

for pesticides and pesticide degradates calculated from determination 

of the analytes in eight reagent-water samples fortified at concentrations 

from 0.015 to 0.1 microgram per liter 45 

11. Number of replicates required to determine estimated holding time of 

parent pesticides in water and on solid-phase-extraction columns 50 

12. Number of replicates required to determine estimated holding time of 

degradates in water and on solid-phase-extraction columns 51 

13. Statistical data used to determine estimated holding time of parent pesticides 

on dry solid-phase-extraction columns maintained at 25 degrees Celsius 52 

14. Statistical data used to determine estimated holding time of degradates 

on solid-phase-extraction columns maintained at 25 degrees Celsius 53 

15. Statistical data used to determine estimated holding time of parent 

pesticides in pesticide-grade water maintained at 4 degrees Celsius 56 

16. Statistical data used to determine estimated holding time of degradates 

in pesticide-grade water maintained at 4 degrees Celsius 57 

17. Bias and variability data from reagent-water-set samples fortified with 

analytes at low (0.1 microgram per liter) concentrations 

and analyzed during March through December, 1999 58 

18. Analytes qualified as estimated concentration because of large bias and 

variability results of fortified reagent-water-set samples (table 17) or short 

holding-time results (tables 13–16) 62 

19. Equipment and supplies required for broad spectrum pesticide analysis 

(methods 2010 and 2011) by on-site solid-phase extraction 69 

iv Contents 
CONVERSION FACTORS 

Multiply By To obtain

Length

centimeter (cm) 3.94 x 10-1 inch 

micrometer (μm) 3.94 x 10-5 inch 

millimeter (mm) 3.94 x 10-2 inch 

meter (m) 3.281 foot 

Mass 

gram (g) 3.53 x 10-2 ounce 

kilogram (kg) 2.205 pound 

microgram (μg) 3.53 x 10-8 ounce 

milligram (mg) 3.53 x 10-5 ounce 

nanogram (ng) 3.53 x 10-11 ounce 

Volume

liter (L) 2.64 x 10-1 gallon 

liter (L) 33.81 ounce, fliud 

microliter (μL) 2.64 x 10-7 gallon 

milliliter (mL) 2.64 x 10-4 gallon 

milliliter (mL) 1 cubic centimeter 

Pressure 

kilopascal (kPa) 1.45 x 10-1 pounds per square inch 

Area 

hectares (ha) (or) hectometer2

 (hm2) 2.471 acres

Concentration, 

in water 

nanograms per liter (ng/L) 1 parts per trillion (ppt) 

micrograms per liter (μg/L) 1 parts per billion (ppb) 

milligrams per liter (mg/L) 1 parts per million (ppm) 

Degree Celsius (oC) may be converted to degree Fahrenheit (oF) by using the following

equation: 

oF = 9/5 (oC) + 32. 

Contents v
ACRONYMS AND ABBREVIATIONS

A ampere 

cm/sec centimeter per second 

dc direct current 

μg/L microgram per liter

mg/L milligram per liter

min minute

mL/min milliliter per minute

ng/L nanogram per liter

ng/μL nanogram per microliter

lb/in2 pound per square inch 

V volt 

± plus or minus 

< less than

C-18 octadecyl 

CCV continuing calibration verification 

ETFE ethylenetetrafluoroethylene 

GC gas chromatography

GC/MS gas chromatograph/mass spectrometer

GCC glass bottle, amber

HPLC high-performance liquid chromatography

ID inside diameter 

IS internal standard 

LRL laboratory reporting level 

LT–MDL long-term method detection level 

MDL method detection limit 

MS mass spectrometry

NAWQA National Water-Quality Assessment program 

NWIS National Water Information System

NWQL National Water Quality Laboratory

OD outside diameter 

PAH polycyclic aromatic hydrocarbon 

PFA perfluoralkoxy

PFTBA perfluorotributylamine 

LRL laboratory reporting level 

SIM selected-ion monitoring

SPE solid-phase extraction 

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

vi Contents 
GLOSSARY

Analyte – The pesticide or pesticide degradate determined in an analysis. 

Continuing calibration verification (CCV) – A calibration standard that contains 

method analytes that is used to measure and control the bias of the existing calibration 

curve for these analytes. The CCV is an instrumental standard only and is not processed 

through preparative steps of the method. 

Fortified reagent-water-set sample – A quality-control sample prepared by

adding a known amount of analytes to a reagent-water sample and analyzed with each set 

of environmental samples (usually 10). Also known as a "set spike."

Internal standard (IS) – An analyte not expected to be found in any environmental 

sample that is added to every sample extract in a known amount. The internal standard is 

used to measure the relative GC/MS responses of other analytes and surrogates in each 

sample. 

Laboratory reporting level (LRL) – The concentration where the false-positive

error is minimized to no more than 1 percent and the false-negative error is minimized to 

no more than 1 percent. The LRL is calculated as 2 times the MDL. An analyte

determined to be not identified, confirmed, or measured in a sample is reported as <LRL. 

Method detection limit (MDL) – The minimum concentration of an analyte that

can be measured and reported with 99-percent confidence that the analyte concentration 

is greater than zero. At this concentration the false positive error is minimized to no 

more than 1-percent probability (U.S. Environmental Protection Agency, 1997). 

Procedural internal standard quantitation – A quantitation method where the 

internal standard is added to the sample extract prior to evaporation and transfer-to-vial 

sample processing steps. These final steps in the sample-extract processing are included 

in the quantitation. Use of the procedural internal-standard quantitation compensates for 

any bias in the extract evaporation and transfer-to-vial sample processing steps, but not 

the solid-phase extraction and elution steps of the analytical method. 

Surrogate – An analyte not expected to be found in any environmental sample that 

is added to every sample in a known amount prior to sample processing. The surrogate is 

used to monitor method performance for each sample. 

Contents vii
Methods of Analysis by the U.S. Geological Survey National 

Water Quality Laboratory—Determination of Moderate-Use 

Pesticides and Selected Degradates in Water by C-18 Solid-Phase 

Extraction and Gas Chromatography/Mass Spectrometry

By Mark W. Sandstrom, Max E. Stroppel, William T. Foreman, 

and Michael P. Schroeder

U.S. Geological Survey Method O-2002-01 

Laboratory Methods (Schedules) 2002 and 2011 

Abstract

A method for the isolation and analysis 

of 21 parent pesticides and 20 pesticide 

degradates in natural-water samples is 

described. Water samples are filtered to 

remove suspended particulate matter and then

are pumped through disposable solid-phaseextraction columns that contain octadecylbonded porous silica to extract the analytes. 

The columns are dried by using nitrogen gas, 

and adsorbed analytes are eluted with ethyl

acetate. Extracted analytes are determined by

capillary-column gas chromatography/ 

mass spectrometry with selected-ion 

monitoring of three characteristic ions. The 

upper concentration limit is 2 micrograms per 

liter (μg/L) for most analytes. Single-operator

method detection limits in reagent-water 

samples range from 0.001 to 0.057 μg/L. 

Validation data also are presented for 14 

parent pesticides and 20 degradates that were 

determined to have greater bias or variability, 

or shorter holding times than the other

compounds. The estimated maximum 

holding time for analytes in pesticide-grade

water before extraction was 4 days. The 

estimated maximum holding time for analytes

after extraction on the dry solid-phaseextraction columns was 7 days. An optional 

on-site extraction procedure allows for 

samples to be collected and processed at 

remote sites where it is difficult to ship 

samples to the laboratory within the

recommended pre-extraction holding time. 

The method complements existing U.S. 

Geological Survey Method O-1126-95 

(NWQL Schedules 2001 and 2010) by using

identical sample preparation and comparable

instrument analytical conditions so that 

sample extracts can be analyzed by either 

method to expand the range of analytes 

determined from one water sample. 

INTRODUCTION 

Pesticides are widely used in the United 

States to increase production of agricultural 

products by controlling weeds, insects, and 

other pests in a wide variety of settings. More

than 450 million kilograms of pesticides, 

which include insecticides, herbicides, and 

fungicides, are used each year in the United 

States. The fate of pesticides after application 

is important because of the potential adverse

effects of pesticides on the environment and 

human health, especially by movement into 

the hydrologic system. Small concentrations 

of pesticides have been widespread in 

surface- and ground-water samples for several 

decades (Barbash and Resek, 1996; Gilliom 

and others, 1999; Larson and others, 1997; 

Larson and others, 1998). 

Pesticides, as is the case for most 

organic compounds, also are transformed 

after release to the environment. Both

Introduction 1
chemical and biological processes might 

cause these transformations. The fate of the 

transformation products, referred to as 

degradates, in surface and ground water is 

frequently not known because degradates are 

not commonly included in monitoring studies. 

Recent interest in the presence and fate of 

degradates, however, has increased. Limited 

studies have indicated that when included in 

surveys, degradates are frequently detected, 

often at higher frequencies and concentrations 

than many parent pesticides. In addition, an 

understanding of the presence of degradates 

can help provide an understanding of the 

overall fate and behavior processes of 

pesticides. 

There are two main reasons why

degradates have not been included in previous 

routine monitoring studies, even after the 

recognition that their presence might be 

relevant to evaluate environmental health. 

First, many degradates are more polar than 

their parent pesticides because the 

transformation processes generally add 

oxygenated or other polar functional groups 

to the molecule. These more polar degradates 

are typically more difficult to analyze by

common gas chromatography (GC) methods. 

Second, and more importantly, analytical 

standards of many potential degradates have 

not been widely available until recently, so 

they could not be included in quantitative

analytical methods. 

The U.S. Geological Survey (USGS)

recently developed two analytical methods for 

the routine determination in water of many of

the pesticides used nationally in greatest 

abundance (Werner and others, 1996; Zaugg

and others, 1995). These methods were used 

in the National Water-Quality Assessment 

(NAWQA) program as part of a study of the 

presence and distribution of pesticides in 

surface- and ground-water samples 

nationwide (U.S. Geological Survey, 2000). 

Those methods included only three 

degradates, and did not include all of the top 

120 pesticides used nationally, one of the 

program goals. 

The methods are referred to by

laboratory personnel and field teams 

requesting analytical services by National 

Water Quality Laboratory (NWQL)

schedules. The laboratory schedules are 

identified for the benefit of readers of this 

report. NWQL schedules 2001 and 2010 

request analyses of 47 pesticides that are 

isolated from filtered water by C-18 solidphase extraction (SPE) and identified and 

quantified by gas chromatography/mass 

spectrometry (GC/MS) (Zaugg and others, 

1995). The pesticide acetochlor was added to 

the methods in June 1994 (Lindley and others, 

1996). NWQL schedules 2050 and 2051 

request analyses of 41 pesticides that are 

isolated from filtered water by Carbopak-B

SPE and are identified and quantified by highperformance liquid chromatography (HPLC) 

with diode-array detection (Werner and 

others, 1996). Both methods have optional 

procedures for on-site SPE. Schedules 2010 

and 2051 request analyses of pesticides in 

samples that were extracted from filtered 

water samples on-site, whereas schedules 

2001 and 2050 request analyses for pesticides 

that were extracted from water samples at the

NWQL. For the purposes of this report, 

schedules 2001 and 2010 will be referred to 

as method 2001, and schedules 2050 and 

2051 will be referred to as method 2050. The 

new method presented in this report will be 

referred to as method 2002, even though field 

teams will need to request either schedules

2002 or 2011. 

This report describes a method for 

determining a broad range of pesticide 

chemical classes and pesticide degradates in

environmental water samples. It was 

developed by the USGS for use in the 

NWQL. The method combines octadecyl 

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

2
(C-18) SPE for pesticide isolation GC/MS 

operated in the selected-ion monitoring mode 

(SIM) for selective confirmation and 

quantitation of the analytes.

1

 The method 

was developed to complement method 2001 

by using the same sample preparation and 

analytical steps but adds new analytes. 

Extracts from method 2001 can be analyzed 

by the new method 2002 to expand the range 

of analytes determined from one water 

sample, because the same sample preparation 

procedures are followed. The method was 

implemented in the NWQL in March 1999 for 

conditional analysis of environmental samples 

collected as part of the NAWQA program. 

This report provides a detailed 

description of all aspects of the methods, 

including the equipment, reagents, sampling

protocol, instrument calibration, and SPE 

procedure required for sample analysis. 

Method performance (bias and variability), 

holding times in water and after isolation on 

the SPE column, and estimated method 

detection limits for 75 analytes are presented. 

The scope of the report includes 

determination of method performance in 

reagent-water samples and in two naturalwater types—a ground-water and a surfacewater sample from the Denver, Colorado, 

region. Method performance was determined 

at two concentration levels—0.1 and 1.0 

microgram per liter (μg/L)—in each water 

type. Method detection limits were estimated 

according to an accepted statistical procedure 

(U.S. Environmental Protection Agency, 

1997). Holding times of the analytes in water 

before extraction and on the SPE columns 

following extraction and column drying were 

evaluated. An optional laboratory automated 

procedure is described, and an optional onsite SPE procedure is briefly described in 

Supplements A and B in this report. 

 

1

Words in boldface are defined in the Glossary.

INITIAL METHOD DEVELOPMENT

This method was developed to 

complement the existing method 2001 by

adding a new suite of pesticides and pesticide

degradates without modifying the analytical 

procedure. Method development consisted of 

testing the new analytes by using the 2001 

procedure and collecting method validation 

information on the analytes that were suitable to 

the GC/MS and SPE conditions used. Initial 

method development included obtaining

analytical standards of the parent pesticides and 

degradates identified as candidate analytes. 

The new analytes were tested by GC/MS and 

deemed acceptable if they provided measurable

response and narrow chromatographic peak 

shapes. The analytes then were combined into

mixtures of parent or degradates and added to 

reagent-water samples to determine initial 

feasibility of recovery using C-18 SPE. The

analytes that were tested initially but 

subsequently eliminated from the method 

because of low GC/MS response or C-18 SPE

recovery are listed in table 1. 

Eight parent pesticides, most of which 

were selected because of their high national-use 

rate, had low or no GC/MS response (xgc) and 

were eliminated from additional testing 

(table 1). Acephate and methamidophos had 

low SPE recovery (xspe), and chlorethoxyfos 

was not obtained in time to include in testing

(xor). Likewise, 14 degradates had low or no 

GC/MS response (xgc), and 9 degradates had 

low SPE recovery (xspe) during preliminary

testing, so the compounds were not included in 

additional testing. Nine degradates listed in 

vendors' catalogs were out of stock during

testing and therefore could not be considered 

for method validation (xor). 

Initial Method Development 3
4 Determination of Moderate-Use Pesticides and Selected Degradates in Water

 by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry 

T

a

ble 1. Analytes that w

ere initially considered or tested but subsequently eliminated from c

o

mplete validation experiments because of problems

with ordering, analysis, or r

e

c

over

y

 [A

nalytes separated by parents and degradates, and sorted accordin

g to ran

k. Parent pesticides s

hown for correspondin

g degradates. Rank, national

pesticideuse ran

k of analyte; C

ASRN, C

hemical Abstracts Service Registry Nu

mber; P-Code, National Water Information System parameter code; xor, 

problem obtainin

g chemical standard; x

gc, problem with gas chro

mato

grap

h/mass spectro

meter analysis; xspe, problems with solid-phase extraction

recovery or instability in water; VOC, volatile organic compou

n

d; 2002x, parent pesticide initially tested but eliminated from

method; –, no C

ASRN or 

parameter code available] 

Ran

k

C

A

S

R

N P-Co

d

e Sh

ort n

a

m

e

U

s

e

Cla

s

s Pro

blem Parent CASRN Parent name Parent class Parent method 

Parent pesticides 

37 30560-19-1 61579 Acephate Insecticide Organophosphorus

xspe –

–

–

–

58 87674-68-8 61588 Dimethenamid

Herbicide A

mide x

gc –

–

–

–

70 59669-26-0 61608 T

hiodicarb Insecticide Carbamate x

gc –

–

–

–

78 133-06-2 61582 Captan

Fungicide Imide xgc

–

–

–

–

98 10265-92-6 61597 Met

hamidophos Insecticide Organophosphorus

xspe –

–

–

–

101 115-32-2 61587 Dicofol Acaricide Organochlori

ne x

gc –

–

–

–

104 76-06-2 61584 C

hloropicri

n

F

u

migant V

O

C

x

gc –

–

–

–

153 300-76-5 38856 Naled Insecticide Organophosphate 

x

gc –

–

–

–

155 66841-25-6 61609 Tralomet

hrin Insecticide Pyret

hroi

d

x

gc –

–

–

–

233 95465-99-9 61581 Cadusaphos

Nematoci

de Organophosphorus

x

gc –

–

–

–

234 54593-83-8 61583 C

hloret

hox

yfos Insecticide Organophosphorus

xor –

–

–

–

Degradates

1003 120-83-2 34602 2,4-

Dichlorophenol

Degradate –

xspe 94-75-7 2-4,D

C

hlorophenox

y

acid 

2050 

1007 – 61619 2-

C

hloro-2’,6’

_alide Degradate –

xor 15972-60-8 Alachlor Acetanilide 2001

1012 6515-38-4 61626 3,5,6-

Trichlor_di

nol Degradate –

x

gc 2921-88-2 C

hlorpyrifos

Organothiophosphate 2001 

1016 10548-10-4 61675 Terbufos-sulfoxide Degradate –

xor 13071-79-9 Terbufos

Organothiophosphate 2001 

1026 – 61658 Metrib

uzin-des_i

keto Degradate –

xspe 21087-64-9 Metrib

uzin

Triazi

ne 2001

1026 – 61657 Metrib

uzin-desamino Degradate –

xspe 21087-64-9 Metrib

uzin

Triazi

ne 2001

1028 1113-02-6 61639 O

met

hoate Degradate –

xspe 60-51-5 Dimethoate Organothiophosphate 2002 

1034 2588-04-7 61667 Phorate sulfone Degradate –

xspe 298-02-2 Phorate Organothiophosphate 2001 

1043 – 61622 3-(2,2-

Dichlor_ aci

d

Degradate –

x

gc 52645-53-1 Permet

hrin Pyret

hroi

d 2001
T

a

ble 1. Analytes that w

ere initially considered or tested but subsequently eliminated from c

o

mplete validation experiments because of problems

with ordering, analysis, or r

e

c

over

y—Continued 

Initial Method Development 5 

Ran

k

C

A

S

R

N P-Co

d

e Sh

ort n

a

m

e

U

s

e

Cla

s

s Pro

blem Parent CASRN Parent name Parent class Parent method 

1049 100-02-7 34647 4-

Nitrophenol

Degradate –

xspe 56-38-2 Parat

hion

Organothiophosphate 2001 

1051 2327-02-8 61748 1-(3,4-

Dichlor_)urea Degradate –

x

gc 330-55-2 Linuron

Urea 2001

1060 35884-76-5 61653 Malathion mono_ acid 

Degradate – 

xor 121-75-5 Malathion

Organothiophosphate 2001 

1064 65600-62-6 61612 2,3,3-trichlor_ salt Degradate –

x

gc 2303-17-5 Triallate T

hiocarbamate 2001

1069 3964-56-5 61632 4-Bromo-2-chlo_henol

Degradate –

xspe 41198-08-7 Profenofos

Organothiophosphate 2002 

1070 16752-77-5 49296 Met

homyl Degradate –

x

gc 59669-26-0 T

hiodicarb

Carbamate 2002x

1070 13749-94-5 61655 Met

homyl-oxime Degradate –

x

gc 59669-26-0 T

hiodicarb

Carbamate 2002x

1078 –

–

Tetrah

y

drophthalimide Degradate –

xor 133-06-2 Captan Imide 2002

1084 934-32-7 61616 2-

A

minobenzimidazole Degradate –

x

gc 17804-35-2 Benomyl Carbamate 9060

1084 10605-21-7 38736 Carbendazi

m

Degradate –

x

gc 17804-35-2 Benomyl Carbamate 9060

1086 2814-20-2 61621 2-Isopropyl-6-_di

nol Degradate –

xspe 333-41-5 Diazi

non

Organothiophosphate 2001 

1086 962-58-3 61638 Diazi

non, ox

y

g_nalog

Degradate –

x

gc 333-41-5 Diazi

non

Organothiophosphate 2001 

1093 – 61624 3-(3,5-

Dichlor_i

mide Degradate –

xor 36734-19-7 Iprodione A

mide 2002

1101 – 61613 2,4'-Dicofol Byproduct

–

x

gc 115-32-2 Dicofol Organochlori

ne 2002

1114 3739-38-6 61628 3-Phenox

ybenzoic aci

d

Degradate –

x

gc 52315-07-8 C

ypermet

hrin Pyret

hroi

d 2002

1124 31110-62-0 61661 O-Et

h

yl-S-prop_ioate Degradate –

x

gc 13194-48-4 Et

hoprop

Organothiophosphate 2001 

1128 5459-93-8 61659 N-Et

h

yl cycloh_amine Degradate –

xspe 1134-23-2 C

ycloate T

hiocarbamate 2002

1129 – 61623 3-(2,2-

Dichlor_ylate Degradate –

x

gc 68359-37-5 C

yfluthrin

Z

yret

hroi

d 2002

1134 – 61643 Et

hion dioxon

Degradate –

xor 563-12-2 Et

hion

Organothiophosphate 2002 

1227 3761-42-0 61648 Fenthion sulfone Degradate –

xor 55-38-9 Fenthion

Organothiophosphate 2002 

1228 – 61651 Isophenphos-de_log

ue Degradate –

xor 25311-71-1 Isofenphos

Organothiophosphate 2002 

1228 – 61650 Isophenphos-de_ropyl Degradate –

xor 25311-71-1 Isofenphos

Organothiophosphate 2002 

1232 17210-55-8 61673 Temephos sulfoxide Degradate –

x

gc 3383-96-8 Temephos

Organothiophosphate 2002 
ANALYTICAL METHOD

Organic Compounds and Parameter 

Codes: Pesticides and degradates, 

filtered, gas chromatography/mass 

spectrometry, Laboratory methods 

(schedules) 2002 and 2011 

(U.S. Geological Survey 

Method O-2002-01) 

1. Scope and Application 

The method is suitable for the 

determination of low-level concentrations (1

to 1,000 nanograms per liter) of pesticides 

and pesticide degradates in filtered naturalwater samples. The methods are applicable to 

pesticides and degradates that are (1) 

efficiently partitioned from the water phase

onto a C-18 organic phase that is chemically

bonded to a solid porous silica matrix, and (2) 

sufficiently volatile and thermally stable for

gas chromatography. Suspended particulate 

matter is removed from the samples by

filtration, so this method is suitable for 

pesticides and degradates in the dissolved 

phase. The quantity of pesticide dissolved in 

water in relation to that adsorbed to sediment 

depends on the physical and chemical 

properties of the pesticide and the

concentration of suspended sediment in the 

water. 

The sample preparation and essential 

GC/MS operational procedures used for the 

new method are identical to those in method 

2001, which was developed for more 

abundantly and widely used pesticides (Zaugg

and others, 1995). The common preparation 

and operational procedures will allow analysis 

of extracts by either method, or analysis of 

analytes in both methods from one watersample extract. The 2001 method included an 

optional on-site extraction procedure, and 

different laboratory method numbers were 

used to distinguish laboratory SPE (2001) and 

on-site SPE (2010). Similarly, the new 

method numbers distinguish laboratory SPE 

(2002) and on-site SPE (2011). 

The analytes include parent pesticides of 

national importance based on their use and 

application or importance to the reregistration monitoring needs of the U.S. 

Environmental Protection Agency (USEPA) 

Office of Pesticide Programs, and degradates 

of pesticides included in NWQL methods 

2001, 2050, or the new method 2002 

presented in this report (table 2). The USEPA 

is reviewing older pesticides (those initially

registered prior to November 1984) under the 

Federal Insecticide, Fungicide, and 

Rodenticide Act to ensure that they meet

current scientific and regulatory standards 

(U.S. Environmental Protection Agency, 

2001). Selection of parent pesticides was 

based on national pesticide-use information 

from the National Center for Food and 

Agricultural Policy and the Census of 

Agriculture (Majewski, 1997). The pesticides 

were sorted in decreasing order by total mass 

of active ingredient applied and total treated

area. The top 120 were determined by

combining the top 100 in total quantity used 

and the top 100 in total area of land treated 

(80 are in the top 100 by both criteria). The 

120 compounds were considered a high

priority for the NAWQA program (Majewski, 

1997). Fifty-seven of these compounds were 

not included in existing NWQL analytical

methods. These compounds were classified 

by physical attributes, such as chemical class, 

characteristic functional groups, and possible 

analytical technique. Seventeen pesticides 

were considered suitable for testing by

GC/MS and were initially included in these

methods. The USEPA reviewed the resulting

list, and set priorities or added pesticides of

importance to its pesticide re-registration 

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

6
process. Selection of pesticide degradates 

initially was based on whether the parent 

pesticide was determined by NWQL methods 

2001, 2050, or the current method, and 

whether an analytical standard was readily

available. These compounds then were 

classified by physical attributes, such as 

chemical class, available functional groups, 

and whether they would be amenable to the 

C-18 SPE GC/MS analytical method. 

Seventy-three degradates initially were

considered. 

After this selection process, the analytes 

were obtained and tested in initial and final 

validation experiments. The analytes that

successfully passed the final validation 

experiments are listed in table 2. The relations 

of pesticide degradates included in the new 

method to parent pesticides in U.S. 

Geological Survey methods 2001, 2050, and 

2002 are listed in table 3. 

All tables in this report list the average

national-use rank of pesticide or pesticide

degradate to allow sorting of the analytes and 

to provide an easy correlation between parent 

and degradate pesticides. The pesticides 

sorted in decreasing order in total kilograms 

of active ingredient applied and total treated

hectares were assigned numbers indicating

their order (or rank). The arithmetical 

average of the rank on the basis of total 

kilograms of active ingredient applied and 

total treated hectares was calculated and is

termed the "rank" in this report. Degradates 

were arbitrarily assigned a rank of 1000 plus 

the average rank of the parent pesticide. For 

example, 2-[2-ethyl-6-methylphenyl)amino]-

1-propanol and 2-ethyl-6-methylaniline, both 

degradates of metolachlor, which has an 

average rank of 2, are assigned average rank 

1002 (table 3). This ranking procedure 

provides a convenient way to link the 

degradates and parent pesticides in tables and 

figures. 

Because some degradates potentially

can be derived from more than one parent 

pesticide, some of the degradates in table 2 

are listed more than once, in order of the 

national-use rank of the parent pesticide. In

that situation, the degradate was assigned the 

lowest rank, even though the degradate could 

have a different rank, depending on which 

parent it was derived from. For example, 3,4-

dichloroaniline is shown in table 2 with rank 

1033, even though it could be assigned ranks 

of 1036, 1051, and 1241, which correspond to 

the three other potential parent pesticides 

(linuron, propanil, neburon) of high to 

moderate national use. 

A short, 20-character name was used in 

the tables to minimize space taken by lengthy

chemical names. The short name was defined 

as the first 14 characters and the last 5 

characters of a name, joined by an 

underscore: “_”. Common or chemical 

names and corresponding short names are 

listed in table 2. 

The calibration range is equivalent to 

concentrations ranging from 0.001 to 1.0 μg/L

for most analytes. The method detection limit 

(MDL) is not only compound dependent, but 

also depends on sample matrix, instrument 

performance, and other operational sources of 

variation. For all analytes listed in table 2, 

MDLs in pesticide-grade water vary from 

0.001 to 0.7 μg/L. Analytical results are not 

censored at the MDL; if a pesticide meets the 

detection criteria (retention time and mass 

spectra compared to that of a reference 

standard, as defined later in section 11), the 

result is calculated and reported with an

estimated “E” qualifier.

Analytical Method 7
8 D

 by C Ta

ble 2. Pesticides and degradates included in new m

ethod

etermination of Moderate-Use Pesticides and Selected Degradates in Water

-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry 

[Table sorted b

y remark co

de an

d then b

y ran

k. Ran

k, natio

nal ran

k of pesticide based o

n ap

plicatio

n rate. Pesticide degradates were arbitrarily assig

ned a ran

k of

1000 pl

us t

he average ran

k of t

he lowest-ran

ked parent pesticide; C

ASRN, C

hemical Abstracts Service Registry N

u

mber; PCode, Natio

nal Water Informatio

n System

parameter code; I, I

nsecticide; H, Herbicide; Def, Defoliant; N, Nematocide; F, Fungicide; P

GR, Plant Growth Regulator; Deg, Degradate; Fu

m, Fu

migant; IS, Internal 

Stan

dard; SUR, Surro

gate; –, not ap

plicable; E, estimated remark co

de; --,CASRN not available] 

Ran

k

N

a

m

e Sh

ort n

a

m

e CA

S

R

N P-Co

d

e

U

s

e

Cla

s

s

Remark 

code

Parent pesticides 

63 Prometryn Prometryn 7287-19-6 04036 H

Triazi

ne —

69 Profenofos Profenofos 41198-08-7 61603 I Organothiophosphate —71 alpha-Endosulfan alpha-E

ndos

ulfan 959-98-8 34362 I Organochlori

ne —

75 Metalax

yl Metalax

yl 57837-19-1 61596 

F

A

mino acid deri

vative —

106 O

x

yfluorfen

O

x

yfluorfen 42874-03-3 61600 H

Diphen

yl et

her —

108 cis-Propiconazole cis-Propiconazole c-60207-90-11 79846 F

Triazole —

110 trans-Propiconazole trans-Propiconazole t-60207-90-11 79847 F

Triazole —

121 M

yclobutanil Myclobutanil 88671-89-0 61599 F

Tziazole —

126 Fenamiphos

Fenamiphos 22224-92-6 61591 N

Organothiophosphate —

127 Hexazi

none Hexazi

none 51235-04-2 04025 H

Triazi

ne —

128 C

ycloate C

ycloate 1134-23-2 04031 H

T

hiocarbamate —

132 Methidat

hion Met

hidat

hion 950-37-8 61598 I Organothiophosphate —

134 Ethion Et

hion 563-12-2 82346 I Organothiophosphate —

211 (E)-Dimethomorph (E)-

Dimethomorph e-110488-70-51 79844 F Miscellaneous —

212 (Z)-

Dimethomorph (Z)-

Dimethomorph z-110488-70-51 79845 F Miscellaneous —

220 Terbuth

ylazi

ne Terbuth

ylazi

ne 5915-41-3 04022 H

Triazi

ne —

225 Flu

metralin Flu

metralin 62924-70-3 61592 P

G

R Dinitroaniline —

227 Fenthion

Fenthion 55-38-9 38801 I Organothiophosphate —

228 Isofenphos Isofenphos 25311-71-1 61594 I Organothiophosphate —229 Propetamp

hos Propetamp

hos 31218-83-4 61604 I Organothiophosphate —

231 Tebupiri

mp

hos Tebupiri

mp

hos 96182-53-5 61602 I Organothiophosphate —

28 Dimethoate Dimethoate 60-51-5 82662 I Organothiophosphate E30 Trib

up

hos Trib

up

hos 78-48-8 61610 Def Organothiophosphate E

71 beta-Endosulfan beta-E

ndos

ulfan 33213-65-9 34357 I Organochlori

ne E

76 Tefluthrin

Tefluthrin 79538-32-2 61606 I Pyret

hroi

d

E

83 Dicrotophos

Dicrotophos 141-66-2 38454 I Organophosphate E
Table 2. Pesticides and degradates included in new method—Continued 

Analytical Method 

Rank Name Short name CASRN P-Code Use Class Remark 

code

93 Iprodione Iprodione 36734-19-7 61593 F Amide E

102 Cyhalothrin Cyhalothrin 91465-08-6 61595 I Pyrethroid E114 Cypermethrin Cypermethrin 52315-07-8 61586 I Pyrethroid E115 Sulprofos Sulprofos 35400-43-2 38716 I 0rganothiophosphate E125 Phosmet Phosmet 732-11-6 61601 I Organothiophosphate E129 Cyfluthrin Cyfluthrin 68359-37-5 61585 I Pyrethroid E131 Bifenthrin Bifenthrin 82657-04-3 61580 I Pyrethroid E230 Sulfotepp Sulfotepp 3689-24-5 61605 I Organothiophosphate E232 Temephos Temephos 3383-96-8 61607 I Organothiophosphate E

Degradates

1002 2-[2-Ethyl-6-methylphenyl)amino]-1-propanol 2-[2-Ethyl-6-m_panol 61520-53-4 61615 Deg — —1007 2-Chloro-2,6-diethylacetanilide 2-Chloro-2,6-d_ilide 6967-29-9 61618 Deg — —1008 4-(Hydroxymethyl)pendimethalin 4-(Hydroxymeth_halin 56750-76-6 61665 Deg — —1016 Terbufos-O-analogue sulfone Terbufos-O-ana_lfone 56070-15-6 61674 Deg — —1033 3,4-Dichloroaniline 3,4-Dichloroaniline 95-76-1 61625 Deg — —1043 3-Phenoxybenzyl alcohol 3-Phenoxybenzy_cohol 13826-35-2 61629 Deg — —1044 c-Methyl-3-(2,2-dichlorovinyl)-2,2-dimethyl-

(1-cyclopropane)-carboxylate 

c-Methyl-3-(2,_ylate 1 c-61898-95-1 79842 Deg — —

1044 t-Methyl-3-(2,2-dichlorovinyl)-2,2-dimethyl-

(1-cyclopropane)-carboxylate 

t-Methyl-3-(2,_ylate 1 t-61898-95-1 79843 Deg — —

1049 Paraoxon-ethyl Paraoxon-ethyl 311-45-5 61663 Deg — —1060 Malaoxon Malaoxon 1634-78-2 61652 Deg — —1062 2-(4-tert-butylphenoxy)-cyclohexanol 2-(4-tert-buty_xanol 1942-71-8 61637 Deg — —1067 Disulfoton sulfone Disulfoton sulfone 2497-06-5 61640 Deg — —1067 Disulfoton sulfoxide Disulfoton sulfoxide 2497-07-6 61641 Deg — —1071 Endosulfan sulfate Endosulfan sulfate 2 1031-07-8 61590 Deg — —

1076 Tefluthrin metabolite [R 152912] Tefluthrin met_2912] -- 61672 Deg — —1093 3,5-Dichloroaniline 3,5-Dichloroaniline 626-43-7 61627 Deg — —1099 2,5-Dichloroaniline 2,5-Dichloroaniline 95-82-9 61614 Deg — —1124 O-Ethyl-O-methyl-S-propylphosphorothioate O-Ethyl-O-meth_ioate 76960-87-7 61660 Deg — —

 9
10 D

 by C

T

a

ble 2. Pesticides and degradates included in new m

ethod—Continued 

etermination of Moderate-Use Pesticides and Selected Degradates in Water

-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry 

Ran

k

N

a

m

e Sh

ort n

a

m

e CA

S

R

N P-Co

d

e

U

s

e

Cla

s

s

Remark 

code

1126 

Fenamiphos s

ulfone Fenamiphos s

ulfone 31972-44-8 61645 

Deg

—

—

1231 

Tebupiri

mp

hos ox

y

gen analog

ue Tebupiri

mp

hos,_log

ue -- 61669 

Deg

—

—

1002 2-Eth

yl-6-

meth

ylaniline 2-Eth

yl-6-

meth_iline 24549-06-2 61620 Deg

— E 

1012 

C

hlorpyrifos ox

y

gen analog

C

hlorpyrifos,_nalog 5598-15-2 61636 

Deg

— E 

1013 2-A

minoN-isopropylbenzamide 2-

A

minoN-isop_amide 30391-89-0 61617 Deg

— E 

1014 Paraoxon-met

h

yl Paraoxon-met

h

yl 950-35-6 61664 Deg

— E 

1015 4-C

hloro-2-met

h

ylp

henol 4-

C

hloro-2-met_henol 1570-64-5 61633 Deg

— E 

1024 3-Trifluorometh

ylaniline 3-

Trifluoromet_iline 98-16-8 61630 Deg

— E 

1032 1-Naphthol 1-

Naphthol 90-15-3 49295 Deg

— E 

1032 1,4-Naphthaquinone 1,4-

Naphthaquinone 130-15-4 61611 Deg

— E 

1034 Phorate oxon Phorate oxon 2600-69-3 61666 

Deg

— E 

1053 Azinphos-met

h

yl-oxon

Azinphos-met

h

yl-oxon 961-22-8 61635 Deg

— E 

1054 

Fonofos ox

y

gen analog

Fonofos, ox

y

ge_nalog 944-21-8 61649 

Deg

— E 

1071 Endos

ulfan et

her Endos

ulfan et

her 3369-52-6 61642 

Deg

— E 

1076 

Tefluthrin metabolite [R 119364] 

Tefluthrin met_9364] -- 61671 Deg

— E 

1101 4,4'-Dichlorobenzophenone 4,4'-Dichlorob_enone 90-98-2 61631 Deg

— E 

1105 4-C

hlorobenzylmeth

yl sulfone 4-

C

hlorobenzyl_lfone 98-57-7 61634 Deg

— E 

1125 Phos

met oxon Phos

met oxon 3735-33-9 61668 

Deg

— E 

1126 

Fenamiphos s

ulfoxide Fenamiphos s

ulfoxide 31972-43-7 61646 

Deg

— E 

1134 Et

hion monoxon Et

hion monoxon 17356-42-2 61644 

Deg

— E 

1153 Dichlorvos

Dichlorvos 62-73-7 38775 F

u

m

Organophosphate E

1227 

Fenthion s

ulfoxide Fenthion s

ulfoxide 3761-41-9 61647 

Deg

— E 

Internal standards

—

Acenaphthene-d10

Acenaphthene-d10 15067-26-2 — IS

—

—

C

hrysene-d12

C

hrysene-d12 1719-03-5 — IS

—

—

P

henanthrene-d10

P

henanthrene-d10 1517-22-2 — IS

—

—

S

urrogates

—

alpha-HCH-d6, s

urrogate alpha-HCH-d6,_ogate 319-84-6-

d6 99224 SU

R

—

—

Diazinond10, surrogate Diazinond10,_ogate 100155-47-3 99223 SU

R

—

—

1

Letter prefix added to C

ASRN because C

ASRN not available for cis-, trans- or E-, Z-isomers. 2

C

ASRN nu

mber for endos

ulfan s

ulfate was chan

ged from "1031-07-7" to "1031-07-8" i

n t

he electronic (pdf) file, February 4, 2002 (mws).
Table 3. Relation of pesticide degradates included in new method to parent pesticides in U.S. Geological Survey methods

2001, 2050, and 2002 [Table sorted by increasing order of degradate-use rank, then parent pesticide-use rank. Some degradates have more than one possible parent pesticide, but use lowest rank. Degradate rank, national-use rank of degradate used in table 1; P-Code, National Water Information System parameter code;CASRN, Chemical Abstracts Service Registry Number; Degradate short name and corresponding long name given in table 1; --, no CASRN available; –, no Parent method]

Degradate 

rank P-Code CASRN Degradate short name Parent CASRN Parent name Parent method

1002 61620 24549-06-2 2-Ethyl-6-meth_iline 51218-45-2 Metolachlor 20011002 61615 61520-53-4 2-[2-Ethyl-6-m_panol 51218-45-2 Metolachlor 20011007 61618 6967-29-9 2-Chloro-2,6-d

_

ilide 15972-60-8 Alachlor 2001

1008 61665 56750-76-6 4-(Hydroxymeth_halin 40487-42-1 Pendimethalin 20011012 61636 5598-15-2 Chlorpyrifos, _nalog 2921-88-2 Chlorpyrifos 20011013 61617 30391-89-0 2-Amino-N-isop_amide 25057-89-0 Bentazon 20501014 61664 950-35-6 Paraoxon-methyl 298-00-0 Methyl parathion 20011015 61633 1570-64-5 4-Chloro-2-met_henol1 94-74-6 MCPA (and salts and esters) 2050 1015 61633 1570-64-5 4-Chloro-2-met_henol1 94-81-5 MCPB (and salts and esters) 2050 1016 61674 56070-15-6 Terbufos-O-ana_lfone 13071-79-9 Terbufos 20011024 61630 98-16-8 3-Trifluoromet_iline1 2164-17-2 Fluometuron 2050

1032 61611 130-15-4 1,4-Naphthaquinone1 63-25-2 Carbaryl 2001

1032 49295 90-15-3 1-Naphthol1 63-25-2 Carbaryl 2001

1032 61611 130-15-4 1,4-Naphthaquinone1 15299-99-7 Napropamide 2001

1032 49295 90-15-3 1-Naphthol1 15299-99-7 Napropamide 2001

1033 61625 95-76-1 3,4-Dichloroaniline1 330-54-1 Diuron 2050

1033 61625 95-76-1 3,4-Dichloroaniline1 709-98-8 Propanil 20011033 61625 95-76-1 3,4-Dichloroaniline1 330-55-2 Linuron 20011033 61625 95-76-1 3,4-Dichloroaniline1 555-37-3 Neburon 20501034 61666 2600-69-3 Phorate oxon 298-02-2 Phorate 20011044 61629 3 13826-35-2 3-Phenoxybenzy_cohol 52645-53-1 Permethrin 2001

1044 79842 3 c-61898-95-1 c-Methyl-3-(2,_ylate 52645-53-1 Permethrin 20011044 79843 3 t-61898-95-1 t-Methyl-3-(2,_ylate 52645-53-1 Permethrin 2001

1044 79842 3 c-61898-95-1 c-Methyl-3-(2,_ylate 52315-07-8 Cypermethrin 2002

1044 79843 3 t-61898-95-1 t-Methyl-3-(2,_ylate 52315-07-8 Cypermethrin 2002

1044 79842 3 c-61898-95-1 c-Methyl-3-(2,_ylate 68359-37-5 Cyfluthrin 2002

1044 79843 3 t-61898-95-1 t-Methyl-3-(2,_ylate 68359-37-5 Cyfluthrin 2002

Analytical Method 11
12 D

 by C

T

a

ble 3. Relation of pesticide degradates included in new m

ethod to parent pesticides in U.S. Geologic

al Sur

vey m

ethods

2001, 2050, and 2002—Continued 

etermination of Moderate-Use Pesticides and Selected Degradates in Water

-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry Degradate ran

k

P-Code CA

SRN Degr

a

d

ate short name

P

arent CA

SRN 

P

arent name

P

arent method

1049 61663 311-45-5 Paraoxon-eth

yl 56-38-2 Parat

hion 2001

1053 61635 961-22-8 Azinphos-met

h

yl-oxon 86-50-0 Azinphos-met

h

yl 2001

1054 61649 944-21-8 Fonofos, ox

y

ge_nalog 944-22-9 Fonofos 2001

1060 61652 1634-78-2 Malaoxon 121-75-5 Malathion 20011062 61637 1942-71-8 2-(4-tert-buty_xanol 2312-35-8 Propargite 20011067 61640 2497-06-5 Disulfoton sulfone 298-04-4 Disulfoton 20011067 61641 2497-07-6 Disulfoton sulfoxide 298-04-4 Disulfoton 20011071 61590 1031-07-7 Endos

ulfan sulfate 959-98-8 alpha-E

ndos

ulfan 2002

1071 61590 1031-07-7 Endos

ulfan sulfate 33213-65-9 beta-E

ndos

ulfan 2002

1071 61642 3369-52-6 Endos

ulfan et

her 959-98-8 alpha-E

ndos

ulfan 2002

1071 61642 3369-52-6 Endos

ulfan et

her 33213-65-9 beta-E

ndos

ulfan 2002

1076 61671 -- Tefluthrin

met_9364] 79538-32-2 Tefluthrin 2002

1076 61672 -- Tefluthrin

met_2912] 79538-32-2 Tefluthrin 2002

1093 61627 626-43-7 3,5-Dichloroaniline 36734-19-7 Iprodione 20021099 61614 95-82-9 2,5-Dichloroaniline 133-90-4 C

hloramben 2050

1101 61631 90-98-2 4,4'-Dichlorob_enone 115-32-2 Dicofol 4 – 

1105 61634 98-57-7 4-

C

hlorobenzyl_lfone 28249-77-6 T

hiobencarb 2001

1124 61660 76960-87-7 O-Et

h

yl-O-meth_ioate 13194-48-4 Et

hoprop 2001

1125 61668 3735-33-9 Phos

met oxon 732-11-6 Phos

met 2002

1126 61646 31972-43-7 Fenamiphos sulfoxide 22224-92-6 Fenamiphos 20021126 61645 31972-44-8 Fenamiphos sulfone 22224-92-6 Fenamiphos 20021134 61644 17356-42-2 Et

hion

monoxon 563-12-2 Et

hion 2002

1153 38775 62-73-7 Dichlorvos2 300-76-5 Naled 4 – 1227 61647 3761-41-9 Fenthion sulfoxide 55-38-9 Fenthion 20021231 61669 -- Tebupiri

mp

hos,_log

ue 96182-53-5 Tebupiri

mp

hos 2002

1Degradates mig

ht also be formed from one or more of the parent pesticides as a res

ult of thermal degradation of the parent pesticide in the injectio

n

port of t

he gas c

hromatograph d

uring gas c

hromatograph

y/mass s

pectrometry analysis. 2Dichlorvos is also ap

plied as a parent pesticide. 3

Letter prefix added to C

ASRN because C

ASRN not available for cis-, trans- or E-, Z-isomers. 4

Last modifed: February 4, 2002 (mws). 
Permanently E-Coded Compounds. 

Two classes of data are reported from the

method: (1) compounds that are reported 

without qualification, and (2) compounds that 

are always reported as estimated. Compounds 

that are reported without qualification are 

reproducibly well recovered by the method, as 

defined by median recoveries between 60 and 

120 percent and with variation (as indicated 

by the nonparametric statistic, relative Fpseudosigma; Hoaglin, 1983) less than 25 

percent. Estimated-value compounds, which 

are "E-coded" in the data base, do not meet 

these performance criteria for unqualified 

quantification, but are retained in the method 

because the compounds are important owing

to high use or potential environmental effects 

and because analytical performance has been 

consistent and reproducible. Estimated-value 

compounds, when reported, have been 

identified as present with a high degree of 

confidence according to method-specific 

criteria, but greater uncertainty exists in the

quantitative determination of concentration 

than for compounds reported without 

qualification. It is important to note, 

however, that there is no qualitative

difference between unqualified compounds 

and estimated-value compounds. The 

identification of the compounds is equally

reliable, and, in reality, bias and variability

for different compounds span a continuum of 

performance rather than corresponding to 

categories. For example, some unqualified 

compounds perform similarly to estimatedvalue compounds that fall just outside the 

unqualified category criteria. Thus, data users 

should consider the estimated-value 

designation as a categorical warning to pay

extra attention to potential use and adjustment 

of numerical concentration results, but not as 

a distinct boundary between acceptable and 

unacceptable data, as defined at the beginning

of this paragraph. 

2. Summary of Method 

Water samples are filtered at the

collection site by using glass-fiber filters with 

nominal 0.7-μm pore diameter to remove 

particulate material (Sandstrom, 1995). 

About 1 L of the filtered water sample is 

pumped through a disposable, polypropylene 

SPE column that contains porous silica coated 

with an octadecyl (C-18) phase that is 

chemically bonded to the surface of the silica. 

The SPE columns are dried using a gentle

stream of nitrogen to remove residual water. 

The adsorbed analytes (pesticides and 

degradates) then are removed from the SPE

columns by elution with 2 mL of ethyl 

acetate. A procedural internal standard in

toluene is added, and the eluant is further 

evaporated to a small volume (150 μL) using

a gentle stream of nitrogen. 

Extracts are analyzed by a capillarycolumn GC/MS operated in the SIM mode. The

analytes are identified by comparing their 

retention times and selected-ion ratios to 

calibration standards analyzed under the same 

GC/MS conditions. Analytes are quantified by

relating the mass spectrometer (MS) response 

of the quantitation ion of the analyte to the

quantitation ion of an internal standard. 

Quantitation of an analyte at a concentration 

less than the lowest calibration standard or

greater than the highest calibration standard is 

qualified as “estimated” (E) to signify the

lower confidence in the extrapolated 

concentration. 

The internal standard quantitation is a

procedural quantitation method in which the 

internal standard is added to the sample

extract prior to evaporation and transfer-tovial sample-processing steps. The use of the 

procedural internal standard quantitation

compensates for any bias in the extract 

Analytical Method 13
evaporation and transfer-to-vial sampleprocessing steps, but not the SPE and elution 

steps of the analytical method. 

Surrogate analytes, which are added to

each sample in known concentration, are used 

to monitor method performance with each 

sample. 

A reagent-water sample fortified with 

0.1 μg/L of the analytes (a fortified reagentwater-set sample or a set spike) and a 

pesticide-grade blank water sample (a

laboratory reagent blank or set blank) are 

extracted, processed, and analyzed with each 

set of 10 samples. 

3. Interferences 

Interferences might be caused by

organic compounds that have gaschromatograph retention times and 

characteristic ions with a mass identical to 

those of the pesticides and degradates of 

interest. Contaminants in laboratory air, 

solvents, reagents (including water), 

glassware, sample bottles and caps, SPE 

columns, and sample-processing equipment 

can cause artifacts or false positives in the

chromatograms. All of these materials must 

be routinely demonstrated to be free from 

interference [less than the MDL, or long-term 

method detection level (LT–MDL), once 

determined] under conditions of analysis by

analyzing laboratory reagent blanks. 

Glassware must be washed with 

detergent in hot water and rinsed with tap 

water and distilled or deionized water. 

Glassware then should be drained, dried, and 

heated in a laboratory furnace at 450°C for at 

least 4 hours before use. Solvent rinsing with 

methanol, followed by air drying, may be 

substituted for oven heating for other

equipment, including sample collection 

bottles, sample splitters, and filtration 

devices. 

Matrix interferences might be caused by

contaminants that are coextracted from the 

sample. The extent of matrix interferences

will vary, depending on the nature of the

sample matrix. 

Residual chlorine in treated water

samples might cause degradation of some 

analytes, especially organophosphorus 

compounds (Dennis and others, 1979). 

Suitable reagents that might be used to 

dechlorinate chlorinated water samples have

not been tested for their effect on all analytes. 

Pesticide degradates might be formed by

degradation of the parent pesticide in the hot 

injection port of the GC. These degradates are 

considered artifacts of the analytical process, 

and are not representative of the concentration 

of analytes in the water samples. The extent 

of GC injection-port degradation depends on 

a number of factors, including surface 

activity, quantity of coextracted organic

material, and extent of impurities on the

injection-port liner. Degradates that are

susceptible to this thermal degradation are

identified in table 3. For example, 3,4-

dichloroaniline can be formed from thermal 

degradation of diuron if it is in the water

sample. 

4. Apparatus and Instrumentation 

4.1 Manual sample extraction 

4.1.1 Cleaning and elution 

module for SPE columns—Supelco, Inc., 

Visiprep Solid-Phase Extraction Vacuum 

Manifold and Visidry Drying Attachment or 

equivalent. 

4.1.2 SPE pump, ceramic-piston, 

valveless pump—Capable of pumping 0 to 30 

mL/min, with fittings for 3.18-mm outside 

diameter (OD) tubing; Fluid Metering Inc., 

Model QSY - 2 CKC or equivalent. For onDetermination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

14
site SPE, an SPE pump powered by a 12-V dc 

motor is needed; Fluid Metering Inc., Model 

RHB - 0 CKC or equivalent. 

4.1.3 Teflon-perfluoralkoxy 

(PFA) tubing—3.18-mm OD; Cole-Parmer 

Instrument Co., CL-06375-01 or equivalent. 

4.1.4 Tefzel-ethylenetetrafluoroethylene (Tefzel-ETFE) female Luer

connector with 1/4-28 thread—Tefzel-ETFE 

union with 1/4-28 thread, and Tefzel-ETFE 

nut with 1/4-28 thread and 3.18-mm OD 

tubing connector; Upchurch Scientific or 

equivalent. 

4.1.5 Pump control box

(optional)—For 12-V dc pumps, fitted with a

4-A fuse, toggle switch, and 10-ohm 1.58-A 

variable resistor. 

4.1.6 Sample-preparation 

workstation (optional)—For pre-cleaning SPE

column; Zymark Inc., BenchMate II

Workstation or equivalent. 

4.1.7 Bottle-top solvent 

dispenser—Adjustable from 2 to 10 mL; 

Brinkman Dispensette, Van Waters & Rogers 

(VWR) Scientific or equivalent, for adding

solvents to SPE columns during manual 

cleaning and conditioning steps. 

4.1.8 Luer flow-control valves 

(optional) or on-off valves—Constructed of 

inert materials; Burdick & Jackson (B&J)

Inert PTFE flow-control valve, Baxter 

Diagnostics, Inc. or equivalent. 

4.1.9 Vacuum pump—Any

vacuum pump with sufficient capacity to 

maintain a slight vacuum of 1.5 to 3 kPa in 

the cleaning/elution module. 

4.2 Automated sample extraction 

4.2.1 Zymark Inc. AutoTrace 

SPE Workstation—Configured for 3-mL SPE 

columns. The setup conditions and 

processing steps for using the AutoTrace 

Workstation are listed in Supplement A at the 

end of this report. 

In the automated method, 

environmental and quality-control samples 

are extracted in batches of six. The time

required for extraction is 58 minutes. One 

operator typically can process 30 samples in 

an 8-hour day using this apparatus. 

4.3 Manual and automated sample 

extraction 

4.3.1 Micropipets—50- and 100-

μL, fixed- and variable-volume micropipets 

with disposable glass capillaries; VWR 

Scientific or equivalent. 

4.3.2 Analytical balances—

Capable of accurately weighing 1,200 ±1 g

(water samples), 10.0000 g ±0.0001 g (SPE 

columns), and 10.000 g ±0.001 mg (analytical 

standards). 

4.3.3 Automated solvent 

evaporator—The sample extracts are 

concentrated with a Zymark TurboVap LV. 

The TurboVap water bath is set to 30°C, and 

nitrogen gas pressure is adjusted to 28 kPa. 

4.4 Sample analysis 

4.4.1 GC/MS instrument—

Agilent Technologies Model 5890 Series II

gas chromatograph, connected via capillary

direct interface to an Agilent Technologies 

5971 or 5972 mass selective detector (MSD). 

4.4.2 Fused-silica capillary

column—Provides adequate resolution, 

capacity, accuracy, and variability. A 30-m 

by 0.25-mm inside diameter (ID) fused-silica 

capillary column coated with a 0.10-μm 

bonded film of 95-percent dimethyl 5-percent 

diphenyl polysiloxane is used; Agilent 

Technologies HP-Ultra II or equivalent.

Analytical Method 15
4.4.3 Recommended GC 

conditions—Oven, 85°C (hold 1.5 min), then 

program to 240°C at 4°C/min, then program 

to 340°C at 15°C/min and hold for 2 minutes; 

injection port, 225°C; carrier gas, helium; 

column flow nominal 0.65 mL/min (30 

cm/sec linear velocity); injection volume, 

1 μL, splitless injection; split-vent flow, 30 

mL/min; septum purge, 1 mL/min. Total 

analysis time is 49 minutes. 

4.4.4 Mass spectrometer 

conditions—Interface, 290°C; source, 180°C; 

analyzer, 100°C; dwell time, 20 milliseconds; 

mass ions monitored are listed in table 5 (see

section 9, Calibration). 

5. Reagents and Consumable 

Materials

5.1 Helium carrier gas, 99.999 

percent purity. 

5.2 Nitrogen gas, for SPE column

drying and solvent evaporation, ultrapure. 

5.3 SPE columns, Isolute C-18 (EC) 

columns, packed with 500 mg of a C-18 

hydrocarbon phase chemically bonded to 

silica (International Sorbent Technology Ltd., 

Mid Glamorgan, UK). The C-18 phase is 

end-capped to reduce polar secondary

interactions with surficial silanol groups. The 

columns use stainless-steel frits to keep the 

sorbent phase in place. 

5.4 Disposable culture tubes, 

borosilicate glass, 16 by 100 mm, baked at 

450°C for 2 hours; Kimax Brand, VWR or 

equivalent. 

5.5 Glass-fiber filters, 0.7-μm nominal 

pore diameter (GF/F grade), baked at 450°C 

for 2 hours; Whatman, Inc. or equivalent. 

5.6 Glass bottles, amber (GCC),

1,000-mL, 33-mm neck, baked at 450oC for 

2 hours, fitted with Teflon-lined screw caps; 

NWQL GCC or equivalent. 

5.7 Solvents, hexane, toluene, ethyl 

acetate, methylene chloride, and methanol;

B&J Brand ultrapure pesticide quality or

equivalent. 

5.8 Pesticide-grade water, any highpurity water such as ultrapure B&J Brand 

water for high-performance liquid 

chromatography (HPLC) or equivalent, that 

has been tested and demonstrated to be free 

from analytes and interferences in this 

analytical method. 

5.9 Detergent solution, a dilute

mixture (0.2 percent in tap water) of 

laboratory-grade phosphate-free liquid 

detergent; Liquinox, Alconox Inc. or 

equivalent. 

6. Sampling Methods, SampleCollection Equipment, and 

Cleaning Procedures 

6.1 Sampling methods: Use sampling

methods capable of collecting water samples 

that accurately represent the water-quality

characteristics of the surface water or ground 

water at a given time or location. Detailed 

descriptions of sampling methods used by the 

USGS for obtaining depth- and widthintegrated surface-water samples and of 

sampling methods for obtaining ground-water 

samples, and of sample processing (splitting,

filtration, shipping) are described by Wilde 

and others (1999). 

6.2 Sample-collection equipment: Use 

sample-collection equipment, including

automatic samplers, that are free of tubing, 

gaskets, and other components made of 

nonfluorinated plastic material that might 

leach interferences into water samples or sorb 

the pesticides and degradates from the water. 

Material suitable for sample-collection and 

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

16
processing equipment includes fluorocarbon 

polymers (Teflon, ETFE), metals (stainless 

steel, aluminum), glass, and ceramics. 

6.3 Sample filtration: Water samples 

need to be filtered prior to SPE using

procedures described by Sandstrom (1995). 

Filtration removes particulate material that

might block the SPE column. Filter the water

samples as soon as possible after collection, 

preferably at the sample-collection site, 

because filtration removes microorganisms 

that might degrade analytes. 

6.4 Cleaning procedures: Wash all 

sample-collection equipment with phosphatefree detergent, rinse with tap water to remove

all traces of detergent, and finally rinse with

methanol (contained in a Teflon squeezebottle). Allow the methanol to drain and 

evaporate from the equipment. When dry,

cover equipment orifices with aluminum foil. 

If it is not practical for the methanol to 

evaporate from the equipment, use pesticidegrade water to rinse methanol from the

equipment. 

NOTE: Methanol needs to be collected and 

disposed of in accordance with local

regulations. 

6.5 Quality-control samples: 

Collection of quality-control (QC) samples is 

a required component of sample collection for 

water-quality studies. QC samples are

collected, usually at the field site, to identify,

quantify, and document bias and variability in 

data resulting from the collection, processing, 

shipping, and handling of samples by field and 

laboratory personnel. The type, number, and 

distribution of QC samples are determined by

the design and data-quality requirements of

the study. Detailed discussion of the 

description and purpose of QC samples is 

presented by Wilde and others (1999). 

6.5.1 Blanks—The primary

purpose of a blank sample is to identify

potential sources of sample contamination and 

assess the magnitude of contamination with 

respect to concentration of target analytes. 

Field blanks are collected and processed at the 

field site in the same manner and using the

same equipment as the environmental 

sample(s). The field blank is comprised of an 

aliquot of blank water processed sequentially

through each component of the sampling

system. The source solution needed for blank 

samples must be produced and certified by a 

laboratory to have analyte concentrations that

do not exceed a specified method detection 

limit. Pesticide-grade blank water (PBW) and 

volatile-grade blank water (VBW) are

required for blanks that will be analyzed for

pesticides and volatile organic compounds, 

respectively. VBW can also be used for 

pesticide blanks. 

6.5.2 Replicates—The primary

purpose of replicate samples is to identify and 

(or) quantify the variability in all or part of

the sampling and analysis system. 

Replicates—environmental samples collected 

in duplicate, triplicate, or higher multiples—

are considered identical in composition and 

are analyzed for the same chemical properties. 

6.5.3 Fortified matrix samples—

Fortified (spike) samples are used to answer

questions such as "What loss or gain of target 

analytes occurred because of water-matrix

characteristics; the field processing, shipping, 

or handling procedures used; holding time; or

laboratory analytical procedures?" A sample 

is fortified by adding a mixture of target

compounds obtained from the laboratory to an 

environmental sample after the sample has 

been processed. An unfortified environmental sample must accompany each fortified 

sample. Training is required before personnel 

attempt to fortify samples. The fortification 

Analytical Method 17
kits provided to USGS personnel by the 

NWQL include the fortification solution, 

equipment, bottle labels, and detailed 

instructions. The numbers and types of matrix

samples used depend on the objectives and 

data-quality requirements of individual 

studies, as determined by the project chiefs. 

Although analyses for a set of fortified 

samples—laboratory fortified sample, fieldfortified sample, and field-fortified 

replicate—provide the most complete

information relating to the performance of the

analytical method, the data from only

laboratory fortified samples, or perhaps only

one field-fortified sample, could be sufficient 

to meet study needs. 

7. Standards 

7.1 Stock standards: The pesticides

and degradates were obtained as pure materials 

from the USEPA National Pesticide Standard

Repository (Ft. Meade, Md.) or commercial 

vendors (ChemService; EQ Laboratories). 

Deuterated PAH standards in solution were 

obtained from commercial vendors 

(ChemService). Isotopically labelled pesticide

standards of diazinon-d10 and alpha-HCH-d6

were purchased from Cambridge Isotope 

Laboratories (Woburn, Massachusetts). 

7.1.1 Stock internal standard

(200 ng/μL)—Prepare a 200-ng/μL

concentration of PAH internal standard by

accurately weighing, to the nearest 0.001 mg, 

1 mg of the pure material of acenaphthened10, phenanthrene-d10, and chrysene-d12 in a

5-mL volumetric flask and dilute to volume 

with toluene. Alternatively, the mixed stock 

may be obtained from commercial vendors. 

Transfer the stock standards to clean vials and 

store in a freezer. The stock standards are 

stable for about 6 months. 

7.1.2 Stock surrogate (100 

ng/μL)—Prepare a 100-ng/μL concentration 

of surrogate by accurately weighing, to the 

nearest 0.001 mg, 0.5 mg of diazinon-d10 and 

alpha-HCH-d6 in a 5-mL volumetric flask and 

dilute with toluene. Transfer the stock 

standard to clean vials and store in a 

refrigerator at 4°C ± 3°C. The stock 

standards are stable for about 6 months. 

7.1.3 Stock standard (10,000 

ng/μL)—Prepare standards of pesticides and 

degradates of about 10,000 ng/μL by

accurately weighing, to the nearest 0.001 mg, 

50 mg of the pure material in a 5-mL

volumetric flask and dilute with ethyl acetate. 

Transfer the stock standards to clean vials and 

store in a refrigerator at 4°C ± 3°C. The stock 

standards for most compounds are stable for 

about 6 months. 

7.2 Primary combined fortification 

standard (100-ng/μL)—The stock standard or 

standards are used to prepare two primary

combined fortification standards that contain 

pesticides and degradates (there are too many

analytes to include all parents and degradates 

in one solution). Alternatively, mixtures of

the analytes may be obtained from 

commercial suppliers. Prepare a 100-ng/μL

concentration primary combined fortification 

standard by combining appropriate volumes 

of the individual stock standard in a 10- or 5-

mL volumetric flask. Use adjustable

micropipet (0–50 or 0–100 μL) to dispense an 

appropriate volume into the volumetric flask 

and dilute with ethyl acetate. Transfer the 

primary combined fortification standard to a

clean vial and store in a refrigerator. This

standard is stable for about 6 months. 

Alternatively, the primary combined

fortification standard can be purchased as a 

custom mixture from a commercial vendor. 

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

18
7.3 Primary recovery standard 

(1 ng/μL): Prepare a primary recovery

standard by diluting the primary combined

fortification standards in 5-mL volumetric 

flasks with methanol. Store in a refrigerator at

4°C ± 3°C. Add a 100-μL aliquot of this 

primary recovery standard to a 1-L water 

sample to obtain a concentration of 0.1 μg/L

for the method performance-evaluation 

studies. 

7.4 Polycyclic aromatic hydrocarbon 

(PAH) internal standard (1 ng/μL): Prepare a 

dilute solution of the PAH internal standard

stock at 1 ng/μL with toluene. Transfer the 

PAH internal standard to a clean vial and 

store in a refrigerator. This standard is stable 

for about 6 months when refrigerated. A 

100-μL aliquot of this standard is added to 

every sample extract to quantify analyte 

concentrations. 

7.5 Surrogate standard (1 ng/μL): 

Prepare a standard of diazinon-d10 and alphaHCH-d6 from the stock standard in methanol 

at a concentration of 1 ng/μL. Store in a 

refrigerator at 4°C ± 3°C. A 100-μL aliquot 

of this standard is added to every sample to 

monitor the extraction and sample preparation 

process. 

7.6 Calibration standards: Prepare a 

series of working calibration standards in 

toluene that contain all pesticides and 

degradates at concentrations ranging from

0.01 to 20.0 ng/μL, as well as the surrogate 

and the PAH internal standard at a constant 

concentration of 1.0 ng/μL. Prepare these 

calibration standards by appropriate dilutions 

of the 100-ng/μL primary combined 

fortification, and surrogate stock standards 

in 5- or 10-mL volumetric flasks (refer to 

table 4). Alternatively, prepare serial dilutions 

of a 20-ng/μL calibration standard. 

8. Gas Chromatograph/Mass 

Spectrometer Performance 

8.1 Gas chromatograph performance 

evaluation 

8.1.1 The gas chromatograph 

performance normally is indicated by peak 

shape and by the variation of the selectedcompound (pesticide or degradate) response 

factors relative to response factors obtained 

by using a new capillary column and freshly

prepared calibration standards. An example 

of the separation and peak shape of the 

pesticides and degradates is shown in a total 

ion chromatogram of a 0.625-ng/μL standard 

(fig. 1). If peak shape deteriorates or if 

response factors fail to meet the calibration 

criteria, either change the injection liner or 

maintain the capillary column to bring the gas 

chromatograph into compliance. Part of the

inlet end of the capillary column can be

removed to restore performance. Specifically, 

a loss or gain in response greater than 30 

percent for pesticides and degradates 

susceptible to loss on injection indicates a

need for immediate action. 

8.2 Mass spectrometer performance 

evaluation 

8.2.1 Check the mass 

spectrometer prior to analysis for excessive 

water and air that would indicate leaks in the 

vacuum. If detected, locate and fix leaks. 

Also, check the instrument at the beginning of 

each series of analyses to ensure mass 

spectrometer performance according to the 

perfluorotributylamine (PFTBA) tuning 

Analytical Method 19
20 D

 by C

T

a

ble 4. Volum

es of primar

y c

o

mbined f

ortification, internal, and surrogate standards needed to prepare suggested concentr

ations of c

alibr

ation 

standards. F

or c

o

mparison, the equivalent concentr

ation of c

alibr

ation standards in w

ater s

a

mples is shown. 

etermination of Moderate-Use Pesticides and Selected Degradates in Water

-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry 

[n

g/μL, nanogram per microliter; μL, microliter; m

L, milliliter; μg/L, micro

gram per liter] 

Conc

e

ntr

ation of c

alibr

ation standard

s

No

minal co

ncentratio

n, in n

g/μL 0.019 0.039 0.078 0.156 0.312 0.625 1.25 2.5 5.0 10 20 

Volu

me of primary co

mbined fortificatio

n

standard (100 n

g/μL), i

n μL 1.95 3.9 7.8 15.6 15.6 31.2 62.5 125 250 500 1,000

Volu

me of stock internal stan

dard

(200 n

g/μL), i

n μL 50 50 50 50 25 25 25 25 25 25 25 

Volume of stock surrogate sta

n

dard

(100 n

g/μL), i

n μL 100 100 100 100 100 100 100 100 100 100 100 

Final volu

me of calibratio

n stan

dard, in m

L 10 10 10 10 5 5 5 5 5 5 5 

Eq

uivalent co

ncentratio

n in water sample, 

in μg/L1 

0.002 0.004 0.008 0.016 0.031 0.063 0.125 0.250 0.500 1.0 2.0

1If t

he extract volu

me is about 100 μL, t

he nominal “on-col

u

mn” concentration of calibration standards corresponds to actual sample concentrations of 0.002 to

2.0 μg/L.
Figure 1. Selected ion chromatogram of pesticides and degradates in a 0.625-nanogram-per-microliter

(ng/μL) standard. Numbers shown above each peak correspond to analytes listed in table 5. 

Analytical Method 21
criteria outlined in section 8.2.2. In addition, 

initially adjust the mass spectrometer to 

ensure that detection at the established 

reporting-level concentration for each 

selected compound can be achieved. 

8.2.2 Verify the mass 

spectrometer tune prior to each analysis, and 

tune if necessary by using the procedure and 

standard software supplied by the 

manufacturer. Parameters in the tuning

software are set to give ±0.15 atomic mass 

unit resolution at masses 69, 219, and 414 in 

the spectrum of PFTBA. Manually adjust the

resolution so that the mass 69 ion has 100-

percent relative abundance, mass 219 ion is 

20- to 60- percent relative abundance, and 

mass 414 ion is 2- to 7-percent relative 

abundance. Check mass assignments to 

ensure accuracy to ±0.15 atomic mass unit 

and that mass peak widths measured at onehalf the peak height are about 0.5±0.15 

atomic mass unit. A complete quantitative

recalibration with all analytes is needed if the

mass spectrometer is re-tuned for mass or 

resolution. 

8.2.3 Mass spectrometer 

background interference—Leaks of 

atmospheric air into the analyzer, or the 

presence of other compounds, might 

compromise instrument performance. 

Common air background and contaminant 

ions are 18, 28, 32, 40, and 44 atomic mass 

units. Check the air background and print the 

result before beginning an analytical batch

(the group of samples whose data are 

evaluated by the quality-control samples 

associated with them). 

9. Calibration 

9.1 Initial calibration: Eight of the 

eleven calibration standards listed in table 4 are 

recommended to calibrate over the expected 

analytical range of about 2 ng/L to 2 μg/L. 

The highest level standard selected will 

depend on the expected upper concentration 

range of samples. 

9.2 Inject 1 μL of each calibration 

standard into the GC/MS according to the 

GC/MS conditions described in section 4.3 

and tabulate peak area response and 

concentration for each analyte and 

corresponding internal standard. 

Isomers (cis-, trans-, Z/E)—Some of the 

compounds are resolved into two or more 

isomers, depending on the resolution of the 

chromatographic column. In the case of cand t-methyl-3-(2,2-dichlorovinyl)-2,2-

dimethyl-(1-cyclopropane)-carboxylate, Eand Z-dimethomorph, and cis- and transpropiconazole, the peak area of each isomer is

used to calibrate independently, quantitate, 

and report each isomer separately. We

assume that the stock standards contain equal 

amounts of each isomer. Other methods, for 

example, method 2060, report propiconazole 

rather than the individual cis- and transisomers, so in situations in which results from 

the different methods are compared, the sum 

of the cis- and trans-isomers should be 

calculated for comparison. For the pyrethroid 

compounds cypermethrin and cyfluthrin, 

which are resolved into 4 isomers, the peak

areas for each isomer are summed and used 

for calibration and quantitation of the

compound. 

9.3 The GC/MS data-processing

software uses standard regression techniques 

(Miller and Miller, 1993) to construct 

calibration equations and plot calibration 

curves for each analyte. The internal standard 

calibration technique is used, where 

regression of the area ratios (Ac/Ai) against

the concentration ratios (Cc/Ci) is determined

for each analyte after analysis of a series of 

the calibration standards:

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

22
where Ac = area of the quantitation ion for 

the selected compound 

or surrogate compound; 

Ai = area of the quantitation ion for 

the internal standard; 

Cc = concentration of the selected 

compound or surrogate 

compound, in nanograms 

per microliter; and 

Ci = concentration of the internal 

standard, in nanograms per 

 microliter. 

The slope of the calibration curve is 

equivalent to the average response factor 

(RFc) of the analyte relative to the internal

standard. Zero should be included in the 

calibration curve, although the curve does not 

need to be forced through zero. 

For most analytes, linear or quadratic 

regression equations provide the best fit to the

data. For linear regression, the equation 

follows: 

b

C

C

m

A

A

i i

c c   , (1) 

where m = slope of the regression 

 equation, and 

b = intercept of the regression 

 equation. 

Note that the quantitation ratio in equation 1 

can be written as a mass ratio: 

b

M

M

m

A

A

i

c

i

c   , (2) 

where Mi = mass of the internal standard, 

in nanograms; and 

Mc = mass of the selected 

compound or surrogate 

compound, in nanograms.

The quantitation ion and internal standard

used in the calculation are listed in table 5. 

9.4 Calculate the relative retention 

time (RRTc) for each selected compound or 

surrogate compound in the calibration 

solution, as follows: 

 RRTc = 

i RT

RTc , (3) 

where RTc = uncorrected retention time 

of the quantitation ion of 

the selected compound or 

surrogate compound, and 

RTi = uncorrected retention time 

of the quantitation ion of 

the internal standard 

 (acenaphthene-d10, 

 phenanthrene-d10, or 

 chrysene-d12). 

9.5 Verification of initial calibration: 

Analyze a solution prepared from standard 

materials from a source other than those used 

to prepare the initial calibration curve.

Calculate the concentration from the 

calibration curve. The calculated concentration should be within 20 percent of its true 

value. This step verifies the validity of the 

calibration standard materials and the

calibration curve prior to sample analysis. 

10. Procedure 

10.1 Weighing SPE columns: Weigh 

the SPE columns (±0.0001 g) and record the 

weight on the column with waterproof ink. 

NOTE: Recording the weight on the SPE 

columns helps to determine when the columns 

are dry after extraction and drying steps. 

Analytical Method 23
24 D

 by C

T

a

ble 5. Retention tim

e, quantitation ion, and confir

m

ation ions for analytes, surrogates, and internal standards, and s

elected 

ionmonitoring group and internal standard f

or analytes and surrogates

etermination of Moderate-Use Pesticides and Selected Degradates in Water

-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry 

[Analytes sorted b

y retention time. No., compound number sho

wn i

n figure 1; Rank, national pesticide-use rank of a

nalyte; P-Co

de, Natio

nal Water 

Information S

ystem parameter code; Approx., approximate; m/z, mass per u

nit charge; SIM group, selected-ion monitori

n

g group; IS, internal 

stan

dard used for q

uantitatio

n: 1, Acenap

hthene-d10; 2, P

henanthrene-d10; 3, Chrysene-d12; --, not ap

plicable; –, not analyzed] 

N

o. R

ank

P-Code

Short name

Approx. 

retention 

time

(min) 

Qua

ntitation 

ion 

(m/z) 

2d

monitor

ed 

ion 

(m/z) 

3rd

monitor

ed 

ion 

(m/z) 

4t

h

monitor

ed 

ion 

(m/z) 

SIM

group 

IS 

Internal Standards

13

1

-- -- Acenaphthene-d10 17.419 162 –

–

– -- 1

28 -- -- P

henanthrene-d10 25.484 188 –

–

– -- 2

70 -- -- Chr

ysene-d12 40.627 240 –

–

– -- 3

S

urrogates

21 -- 99224 alpha-HCH-d6 23.341 224 222 226 – 15 2

33 -- 99223 Diazi

non-d10, _ogate 26.305 183 153 183 – 15 2 

A

nalytes

1 1024 61630 3-

Trifluoromet_iline 5.784 161 114 142 160 1 1

2 1002 61620 2-Eth

yl-6-

meth_iline 10.750 120 121 135 136 2 1

3 1153 38775 Dichlorvos 10.805 109 185 145 187 24 1015 61633 4-

C

hloro-2-met_henol 11.275 142 77 107 144 2 1

5 1124 61660 O-Et

h

yl-O-meth_ioate 12.652 156 124 128 129 4 1

6 1067 61641 Disulfoton sulfoxide 13.014 212 97 125 153 4 17 1099 61614 2,5-Dichloroaniline 13.100 161 126 163 165 4 1

8 1044 79842 c-Met

h

yl-3-(2,_ylate 13.409 187 163 165 189 5 1

9 1044 79843 t-Met

h

yl-3-(2,_ylate 13.650 187 163 165 189 5 1

10 1093 61627 3,5-Dichloroaniline 15.162 161 126 163 165 6 111 1032 61611 1,4-

Naphthaquinone 15.440 158 102 104 130 6 1

12 1033 61625 3,4-Dichloroaniline 15.994 161 126 163 165 6 114 1032 49295 1-

Naphthol 18.281 144 115 116 – 8 1

15 1002 61615 2-[2-

Eth

yl-6-m_panol 20.332 162 133 163 193 9 1

16 1034 61666 Phorate oxon 21.435 171 143 156 170 10 2

17 1013 61617 2-

A

minoN-isop_amide 21.651 120 119 178 – 10 2

18 128 04031 C

ycloate 21.822 154 155 215 – 10 2
Table 5. Retention time, quantitation ion, and confirmation ions for analytes, surrogates, and internal standards, and selected 

ion-monitoring group and internal standard for analytes and surrogates—Continued 

Analytical Method 25 

No. Rank P-Code Short name

Approx. 

rentention 

time

(min) 

Quantitation 

ion 

(m/z) 

2d

monitored 

ion 

(m/z) 

3rd

monitored 

ion 

(m/z) 

4th

monitored 

ion 

(m/z) 

SIM

group 

IS 

19 83 38454 Dicrotophos 22.979 127 109 193 – 11 220 1076 61671 Tefluthrin met

_

9364] 23.065 181 141 197 – 11 2

22 230 61605 Sulfotepp 23.444 322 193 202 145 11 223 1054 61649 Fonofos, oxyge_nalog 23.565 230 93 109 – 11 224 1007 61618 2-Chloro-2,6-d_ilide 24.001 176 147 177 – 12 2

25 1105 61634 4-Chlorobenzyl_lfone 24.125 89 125 127 – 12 226 28 82662 Dimethoate 24.341 93 87 125 229 12 227 1076 61672 Tefluthrin met

_

2912] 25.401 91 92 197 141 13 2

29 220 04022 Terbuthylazine 25.722 173 138 214 231 14 230 229 61604 Propetamphos 25.895 138 194 222 236 14 231 1043 61629 3-Phenoxybenzy_cohol 25.895 200 171 181 201 14 232 1231 61669 Tebupirimphos,_logue 26.050 245 190 217 260 14 234 1014 61664 Paraoxon-methyl 26.520 109 200 230 247 15 235 76 61606 Tefluthrin 27.122 177 141 178 197 15 2

36 1071 61642 Endosulfan ether 27.251 170 239 193 277 15 237 231 61602 Tebupirimphos 27.411 234 137 152 261 15 238 1060 61652 Malaoxon 28.841 127 142 173 195 16 239 1062 61637 2-(4-tert-buty_xanol 29.192 135 136 150 248 16 240 1049 61663 Paraoxon-ethyl 29.240 109 139 220 275 16 241 63 04036 Prometryn 29.256 241 184 226 199 16 242 75 61596 Metalaxyl 29.256 206 220 146 160 16 243 1016 61674 Terbufos-O-ana_lfone 30.440 183 109 139 184 17 244 1012 61636 Chlorpyrifos, _nalog 30.733 197 109 169 199 17 245 227 38801 Fenthion 30.854 278 109 125 169 17 246 1101 61631 4,4'-Dichlorob_enone 30.923 139 141 250 252 17 247 228 61594 Isofenphos 32.942 213 121 185 255 18 348 132 61598 Methidathion 33.543 85 93 125 145 19 349 71 34362 alpha-Endosulfan 33.896 195 159 170 197 19 3

50 1067 61640 Disulfoton sulfone 34.105 213 125 153 157 20 3
26 D

 by C

etermination of Moderate-Use Pesticides and Selected Degradates in Water

-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry 

T

a

ble 5. Retention tim

e, quantitation ion, and confir

m

ation ions for analytes, surrogates, and internal standards, and s

elected 

ionmonitoring group and internal standard f

or analytes and surrogates—Continued 

N

o. R

ank

P-Code

Short name

Approx. 

rente

ntion 

time

(min) 

Qua

ntitation 

ion 

(m/z) 

2d

monitor

ed 

ion 

(m/z) 

3rd

monitor

ed 

ion 

(m/z) 

4t

h

monitor

ed 

ion 

(m/z) 

SIM

group 

IS 

51 225 61592 Flu

metralin 34.426 143 145 157 159 20 3

52 126 61591 Fenamiphos 34.687 154 153 217 303 21 353 69 61603 Profenofos 35.068 208 97 179 206 21 354 30 61610 Trib

up

hos 35.261 169 170 171 202 21 3

55 121 61599 Myclobutanil 35.610 179 125 181 206 22 356 1134 61644 Et

hion

monoxon 35.851 171 97 125 215 22 3

57 106 61600 O

x

yfluorfen 35.867 252 195 300 361 22 3

58 71 34357 beta-E

ndos

ulfan 36.495 195 159 170 197 23 3

59 1227 61647 Fenthion sulfoxide 36.884 125 109 153 279 24 360 134 82346 Et

hion 37.429 231 97 125 153 24 3

61 115 38716 Sulprofos 37.887 156 139 140 322 25 362 1071 61590 Endos

ulfan sulfate 38.440 272 229 237 274 26 3

63 108 79846 cis-Propiconazole 38.613 173 175 259 261 27 3

64 1125 61668 Phos

met oxon 38.681 160 161 133 268 27 3

65 1008 61665 4-(H

y

drox

ymeth_halin 38.716 268 178 269 297 27 3

66 110 79847 trans-Propiconazole 38.888 173 175 259 261 27 3

67 127 04025 Hexazi

none 39.226 171 83 128 172 28 3

68 1126 61646 Fenamiphos sulfoxide 40.524 304 122 303 – 29 369 1053 61635 Azinphos-met

h

yl-oxon 40.524 132 77 160 – 29 3

71 93 61593 Iprodione 40.644 187 189 244 246 24 372 1126 61645 Fenamiphos sulfone 40.747 320 122 292 – 29 373 125 61601 Phos

met 40.765 93 77 160 – 29 3

74 131 61580 Bifenthrin 41.209 181 165 166 182 30 375 102 61595 C

yhalothri

n 42.780 181 141 197 199 31 3

76 129 61585 C

yfluthrin 44.388 163 165 199 226 32 3

77 114 61586 C

ypermet

hrin 44.709 163 165 181 – 32 3

78 211 79844 (E)-

Dimethomorph 46.318 301 165 166 303 33 3

79 212 79845 (Z)-

Dimethomorph 46.564 301 165 166 303 33 3

80 232 61607 Temephos 47.628 125 203 406 – 34 3
10.2 Precleaning SPE columns:

Columns are precleaned prior to use by using

a vacuum pump (manual procedure) or the 

Zymark BenchMate II Workstation 

(automated procedure). 

10.2.1 Manual procedure 

Preclean the SPE columns by

rinsing with 3 mL of the elution solvent (ethyl

acetate). Allow the solvent to drain by

gravity, then completely remove all solvent 

from the column by either nitrogen positive

pressure or vacuum. Store the cleaned 

columns in 40-mL glass vials or in a 

desiccator at room temperature. 

10.2.2 Automated procedure 

If using the BenchMate II

Workstation, place columns on the rack with 

culture tube and fitting (clean in lots of 100 if 

possible). Program the workstation to rinse 

the lines with ethyl acetate, then sequentially

pump 3 mL ethyl acetate through each 

column and dry the column with nitrogen. 

Store the cleaned columns at room

temperature in closed 40-mL glass vials or in 

a desiccator to minimize sorption of 

contaminants from the laboratory

environment. 

10.3 Precleaning extraction apparatus: 

Set up the SPE pumping apparatus. Use a 50-

mL glass graduated cylinder to contain the 

cleaning solutions and prevent contamination 

of the inlet tubing. Rinse the Teflon-PFA 

tubing and pump with about 50 mL of 

detergent solution, followed by about 200 mL

of tap water and 50 mL of methanol. Turn on 

the pump and adjust the flow rate of the pump 

to between 20 to 25 mL/min by using a

graduated cylinder to measure the volume 

through the SPE column. Ensure that there 

are no leaks in any of the fittings. Keep the 

clean inlet tubing of the pump in the clean 

glass cylinder to avoid contamination of the 

tubing while preparing the sample and SPE 

column. For longer storage, wrap the tubing

in aluminum foil. 

If using the automated AutoTrace 

procedure, rinse the Teflon-PFA tubing and 

pump with about 50 mL of cleaning solution 

of isopropanol: methylene chloride: toluene

(7:2:1), followed by about 50 mL of methanol 

and 100 mL of distilled water. 

10.4 SPE column conditioning: 

Immediately before sample extraction, add 

3 mL of methanol to the SPE column and 

allow the methanol to drain partially through 

the column by gravity. An optional Luer

flow-control valve attached to the male Luer

fitting of the SPE column can be used to 

control the flow of fluids through the SPE 

column. Conditioning is needed to solvate 

the C-18 phase attached to the silica particles 

in the SPE column to ensure maximum 

interaction of the C-18 phase with the sample. 

NOTE: Do not allow the columns to go dry

once conditioning and equilibration have

started. If the fluid level drops below the 

upper frit of the SPE column, air will enter 

the SPE column bed and might prevent 

exposure of the water sample to the SPE C-18 

phase. Maintain levels of fluids by adding

additional fluid or by closing Luer fittings or

flow-control valves. If the column does go

dry, repeat the conditioning process with 

methanol followed by water. 

10.5 SPE column equilibration: Drain 

the methanol to the upper frit of the SPE 

column. Add 3 to 6 mL of pesticide-grade 

water and allow the water and residual 

methanol to drain by gravity through the 

column to the upper frit. About 5 minutes is 

required for each column volume of the 

methanol and water to drip through the 

column. 

Analytical Method 27
10.6 Sample preparation: Water 

samples must have been previously filtered 

(Sandstrom, 1995). Weigh the sample and 

bottle (Ws) and record the gross sample

weight (±1 g). Add methanol to the sample 

equivalent to 1 percent of the sample volume 

(about 9 mL) as a conditioner, and record the 

sample weight (Wm). Add a 100-μL aliquot 

of the surrogate solution (1 ng/μL; section 

7.5) by using a micropipet with a clean 

disposable glass bore for each sample. (This 

step should result in a concentration of 0.1 

μg/L for the surrogates in a 1-L sample.) Cap 

and gently swirl the sample in the bottle to 

mix thoroughly.

NOTE: Allow surrogate and fortified 

standards to come to room temperature before 

adding to samples. 

10.7 Sample extraction: Weigh and 

record the weight (Wc) of a 1,000-mL plastic 

beaker (or similar container) that will be used

to collect the volume of sample processed 

through the column. Place the inlet end of the 

Teflon-PFA tubing into the sample container, 

making sure that the tubing end is positioned 

in the lowest spot of the bottle, and turn on 

the pump. After all air is displaced from the 

tubing, attach the SPE column to the outlet 

fitting of the pump tubing, and collect the

sample that is pumped through the column. 

Ensure that there are no leaks or sources of 

bubbles in the system. Small bubbles might 

form as the sample is pumped through the 

tubing, but they will not cause any problems 

if they accumulate in the pump head. Large 

air bubbles are a problem because they can 

displace the methanol conditioner in the 

column or cause uneven flow. 

NOTE: To avoid contaminating the sample, 

do not handle the outside of the clean section 

of tubing that is placed in the sample bottle. 

Wrap the clean tube in aluminum foil, or 

insert into 0.5-mm ID Teflon-PFA tubing

when not in use. A piece of tape attached to

the top of the tubing indicates which section 

of the tubing can be handled and which 

section is clean and will be in contact with the

sample. 

Pump the entire sample through the SPE 

column at a flow rate of between 20 to 25 

mL/min, and turn off the pump when 

completed. Disconnect the column from the

pump system, and remove residual interstitial 

water with a positive air pressure using a

syringe with a Luer fitting and short length of

silicone tubing to connect the Luer fitting to 

the open end of the SPE column. Weigh the 

extracted water sample, and record the final 

weight (Wa) of the sample processed through 

the column and the collection container. 

Discard the extracted sample according to

appropriate waste-disposal practices, weigh 

the empty sample bottle, and record the tare

weight (Wb). 

10.8 SPE pump cleaning: Clean the 

pump and Teflon-PFA tubing with detergent 

solution, tap water, and methanol (or other 

solvent mixture) to prepare for the next

sample. 

10.9 SPE column drying: All SPE 

columns are dried in the laboratory prior to 

elution. Attach a universal adapter to the 

large, open end of the SPE column. Next

attach the adapter to the male Luer fitting on 

the gas-pressure module of the SPE vacuum 

manifold, and then dry the column using a 

positive pressure (138 kPa for 20 minutes) of 

nitrogen to remove all interstitial water. 

Verify that all water is removed from the

column by periodically weighing the column 

and comparing the weight to the preextraction weight. Store dry columns in a

desiccator (no longer than 7 days) until 

elution. 

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

28
NOTE: Do not dry the column for excessive 

periods. Pesticides and degradates might 

evaporate and be removed in the gas phase. 

10.10 Elution of compounds: Label a 

16- by 100-mm culture tube with sample 

identification and place in a holding rack. 

Add 100 μL of the PAH internal standard (1 

ng/μL; section 7.4) to the culture tube using a 

micropipet or syringe. Place the dried SPE

columns in the appropriate culture tube. The

open end of the SPE column should rest on 

the edge of the culture tube to keep the male

Luer end of the SPE column raised a few 

centimeters above the bottom of the culture 

tube. Add 2 mL of ethyl acetate to the SPE

column, and allow the solvent to drain by

gravity into the culture tube (about 15–20 

minutes). Air pressure (with a 50-mL glass 

syringe) can be used to gently force interstitial 

solvent that remains in the column into the

vial. 

10.11 Evaporation of solvent: Preheat

the TurboVap evaporator water bath to 30°C, 

and adjust the gas pressure to 28 kPa. Place 

culture tubes in the TurboVap evaporator for 

about 15 minutes to concentrate the eluant to 

about 100 μL under a gentle stream of 

nitrogen. Periodically check the sample 

volumes. At no time should the eluant be 

allowed to evaporate completely because this

will result in loss of compounds. 

10.12 Transfer to vials: Use a baked 

disposable glass Pasteur pipet to withdraw 

eluant, and transfer eluant to an appropriately

labeled GC vial that contains a 400-μL insert 

for GC/MS analysis. 

NOTE: A glass syringe fitted with a short 

length of silicone tubing to attach the glass 

Pasteur pipet is the preferred equipment for 

withdrawing eluant into the pipet. Solvent 

vapors in contact with rubber or latex pipet 

bulbs might contaminate the eluant with 

plasticizers. 

Rinse the culture tube with about 150 to 

200 μL of toluene using a syringe to dispense 

the solvent, and take care not to allow the tip 

of the syringe to contact the walls of the 

culture tube. If the tip does contact the culture 

tube, rinse with solvent. Vortex the culture

tube, ensuring the solvent reaches the height

of the original 2-mL solvent volume. 

Transfer the toluene rinse into the GC vial

insert. A 200- to 300-μL volume of extract 

should fill about half the volume of the glass 

insert. Cap the GC vial, and refrigerate until 

GC/MS analysis is performed. 

NOTE: Use of a pipet or squeeze bottle to 

rinse the culture tube is not good practice 

because this might result in excess solvent

and require additional evaporation to obtain 

the desired final volume of about 200 to 

300 μL. 

10.13 Sample analysis and data 

evaluation: Ensure that GC/MS conditions 

for the analysis of the selected compounds in 

sample extracts are the same as those used in

the analysis of the calibration standards. Prior

to the analysis of any sample extracts, ensure 

that the PFTBA mass-spectral performance 

criteria have been met, and that the selectedcompound calibration data conform to the 

criteria set forth above. In addition, optimize 

the system so that the reporting level for each

selected compound can be achieved as 

described in section 8.2. Inject 1 μL of the 

sample extract, and acquire data using the 

GC/MS conditions described in sections 4.4 

and 9. 

11. Calculation of Results 

11.1 Qualitative identification 

11.1.1 The observed retention 

time of the GC peak of the quantitation ion 

for the selected compound of interest needs to 

be within ±6 seconds of the expected 

retention time (RT) based on the RRTc

Analytical Method 29
obtained from the internal-standard analysis 

(eq. 3). The expected retention time is 

calculated as follows: 

 , (4) i RT RRTc  RT

where RT = expected retention time of 

the selected compound 

or surrogate compound in 

 the sample; 

RRTc = relative retention time of the 

 selected compound 

or surrogate compound 

from the calibration 

 standards; and 

RTi = uncorrected retention time 

of the quantitation ion 

of the internal standard in 

 the sample. 

11.1.2 Mass-spectral ions are 

verified for each selected compound by

comparing the relative integrated abundance 

values of the three or four significant ions 

monitored with the relative integrated

abundance values obtained from calibration 

solutions determined by the GC/MS 

according to procedures previously given. 

The relative ratios of the three or four ions 

need to be within ±20 percent of the relative

ratios of those obtained on injection of a 

1-ng/mL calibration solution in the absence 

of any obvious interferences. 

11.2 Quantitation 

11.2.1 Calculate the weight of 

sample processed as follows: 

W = (Wa - Wc) x

Ws - Wb

Wm - Wb , (5)

where W = weight of sample, in grams; 

Wa = weight of sample and collection 

container after SPE, in grams; 

Wc = weight of container used to 

collect sample that passes 

through SPE column, in grams; 

Ws = weight of bottle and sample, 

 in grams; 

Wb = weight of empty sample bottle, 

in grams; and 

Wm = weight of sample, methanol, and 

bottle, in grams. 

11.2.2 If a selected compound has 

passed the aforementioned qualitative

identification criteria, the GC/MS dataprocessing software is used to calculate the 

total mass of the analyte from the calibration 

equations determined in section 9.3. For 

linear regression, the calibration equation is as 

follows: 















   b

i A

Ac

m

Mi M c , (6) 

where Mc = mass of the selected 

compound or surrogate 

compound in the sample, 

 in micrograms;

Mi = mass of the internal 

standard added to 

extract, in micrograms; 

m = slope of regression equation;

Ac = area of the quantitation ion 

for the selected compound or 

surrogate compound identified 

in the sample; 

Ai = area of the quantitation ion 

for the internal standard 

in the sample; and 

b = intercept of regression equation.

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

30
The mass of the internal standard added is 

calculated as follows: 

 , (7) i V i C Mi 

where Mi = mass of the internal standard 

added to extract, in 

 micrograms;

Ci = concentration of the internal 

standard added to extract, in 

nanograms per liter; and 

Vi = volume of the internal standard 

(section 7.4) added to 

extract, in microliters. 

The concentration of the analyte in the sample

is calculated as follows: 

W

Mc Cc  , (8) 

where Cc = concentration of compound, 

in micrograms per liter; 

Mc = mass of the compound, in 

 mircrograms; and 

 W = volume of the sample, in liters 

(assume 1.0 g = 1.0 mL). 

11.2.3 The percent recovery of the 

surrogate compounds is calculated as follows: 

100



 





  Cs Vs

Mc R , (9) 

where R = recovery of the surrogate 

compound, in percent; 

Mc = mass of the surrogate in the 

sample, in micrograms 

(from eq. 6); 

Cs = concentration of the surrogate 

compound in the surrogate 

standard (section 7.5) 

added to the sample, in 

micrograms per microliter; and 

Vs = volume of the surrogate 

standard added to the sample, 

 in microliters. 

12. Reporting of Results 

This method was designed for use in 

studies of pesticide concentrations in water in 

a variety of seasons and land-use settings for

which the best possible information about the 

presence and concentration of a pesticide in

filtered water is needed. Consequently, 

results are not censored at a low reporting

limit for detected pesticides. Results 

calculated to be less than the lowest 

calibration standard (equivalent to 0.002 μg/L

in a water sample for most compounds; table 

4) are qualified as “estimated” (E) to signify

the lower confidence in the extrapolated 

concentrations. 

Concentrations of pesticides are 

reported to the NWIS data base as follows. If

the pesticide is not detected, the result is 

reported as less than the laboratory 

reporting level (LRL) (for example, <0.002). 

If the concentration is within the calibration 

range, the result is reported to three

significant figures. If the concentration is less 

than the LRL or lowest calibration standard, 

the concentration is reported to two 

significant figures, and is labelled with the

estimated “E” remark to signify the lower 

confidence in the extrapolated concentration. 

Similarly, if the concentration is greater than

the highest concentration standard, the 

concentration is reported to two significant 

figures and the "E" code is used. Other 

situations in which the “E” qualifier is used

Analytical Method 31
include when the continuing calibration 

verification (CCV) standard is outside of 

expected limits and the set is not reanalyzed, 

or any time the analyst feels the quantitation 

might not be accurate. 

FINAL METHOD VALIDATION 

Analytes that passed both initial GC/MS 

and SPE validation experiments were used in 

additional quantitative validation studies of

bias and variability in three water types 

(pesticide-grade water, surface water, and 

ground water) at two nominal concentrations 

(0.10 and 1.0 μg/L), and at a low 

concentration (0.015 to 0.10 μg/L) to 

determine initial MDLs. In addition, holdingtime experiments on the SPE column and in 

water were conducted. 

A reagent-water sample, a surface-water 

sample collected from Boulder Creek near 

75th Street, Boulder, Colo., and a groundwater sample collected from a monitor well 

near the wastewater-treatment plant in

Denver, Colo., were used to test method 

performance. The reagent-water sample was 

split into four sets of eight subsamples each. 

One set of eight subsamples was fortified with 

0.10 μg/L of each parent analyte, and the 

other set of eight subsamples was fortified 

with 1.0 μg/L of each parent analyte. The 

other two sets of eight subsamples were 

fortified with 0.10 and 1.0 μg/L of each 

degradate, respectively. Parent pesticides 

were analyzed separately from degradates to

assess formation of degradates during sample

processing and analysis. 

Each of the surface- and ground-water 

samples was split into 17 1-L subsamples. 

One set of eight subsamples was fortified with 

0.10 μg/L of each analyte, and the other set of 

eight subsamples was fortified with 1.0 μg/L

of each analyte. In addition, unfortified 

samples of the surface water and ground 

water were extracted and analyzed to

determine background concentrations of the 

pesticides. All subsamples were analyzed at

the National Water Quality Laboratory using

one GC/MS. Each sample set was fortified, 

extracted, and analyzed on different days

during June–July 1999, so comparison of 

different matrices and concentrations includes 

bias from day-to-day variation. The surfaceand ground-water samples did not require 

correction for background concentrations of 

analytes because no analytes were detected in

either unfortified sample. Summaries of

recovery and variability of the analyses are

provided in tables 6 through 9. 

The percent recovery of the analytes is

calculated as follows: 

R = 100 ( )

n

s u

C

C C

 , (10) 

where R = recovery of the pesticide or 

pesticide degradate, in percent; 

Cs = measured concentration in the 

fortified sample, in micrograms 

 per liter; 

Cu = measured concentration in the 

unfortified sample, in micrograms 

per liter (use 0 for reagent-water 

 sample); and 

Cn = nominal (theoretical) concentration 

increase that results from fortifying 

the sample, in micrograms per liter. 

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

32
Final Method Validation 33 

Table 6. Bias and variability data from eight reagent-water samples fortified with parent pesticide analytes at high (1.0 microgram per liter) 

and low (0.1 microgram per liter) concentrations [Analytes are separated into parent pesticides and degradates and sorted by remark code and then by rank. Presence of degradate indicates breakdown of 

corresponding parent pesticide during sample preparation or analysis. Recovery of degradate based on expected concentration of parent pesticide. Rank, national application and use rank of pesticide; P-Code, National Water Information System parameter code; μg/L, microgram per liter; F-pseu, F-pseudosigma (interquartile range/1.349); Rel F-pseu, relative F-pseudosigma; –, not applicable; --, not analyzed; E, estimated remark code] 

High Low 

Rank P-Code Short name Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent)

Rel 

F-pseu 

(percent) 

 Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent) 

Rel 

F-pseu 

(percent) 

Remark

code 

Parent pesticides 

63 04036 Prometryn 0.950 0.0379 95.0 4.0 0.0838 0.0034 83.8 4.1 – 69 61603 Profenofos 0.680 0.0184 68.0 2.7 0.0671 0.0035 67.1 5.2 – 71 34362 alpha-Endosulfan 0.799 0.0123 79.9 1.5 0.0799 0.0026 79.9 3.2 – 75 61596 Metalaxyl 0.934 0.0426 93.4 4.6 0.0858 0.0033 85.8 3.9 – 

106 61600 Oxyfluorfen 0.538 0.0485 53.8 9.0 0.0527 0.0042 52.7 7.9 – 108 79846 cis-Propiconazole 0.673 0.0127 67.3 1.9 0.0696 0.0020 69.6 2.8 – 

110 79847 trans-Propiconazole 0.714 0.0085 71.4 1.2 0.0697 0.0034 69.7 4.8 – 

121 61599 Myclobutanil 0.784 0.0136 78.4 1.7 0.0663 0.0033 66.3 5.0 – 126 61591 Fenamiphos 0.572 0.0192 57.2 3.4 0.0724 0.0023 72.4 3.1 – 127 04025 Hexazinone 0.578 0.0261 57.8 4.5 0.0515 0.0013 51.5 2.6 – 128 04031 Cycloate 0.829 0.0155 82.9 1.9 0.0803 0.0029 80.3 3.7 – 132 61598 Methidathion 0.795 0.0189 79.5 2.4 0.0716 0.0018 71.6 2.5 – 134 82346 Ethion 0.627 0.0344 62.7 5.5 0.0503 0.0015 50.3 3.0 – 211 79844 (E)-Dimethomorph 0.698 0.0119 69.8 1.7 0.0811 0.0044 81.1 5.4 – 212 79845 (Z)-Dimethomorph 0.683 0.0136 68.3 2.0 0.0824 0.0032 82.4 3.8 – 220 04022 Terbuthylazine 1.052 0.0568 105.2 5.4 0.1000 0.0044 100.0 4.4 – 225 61592 Flumetralin 0.534 0.0484 53.4 9.1 0.0520 0.0036 52.0 7.0 – 227 38801 Fenthion 0.988 0.0337 98.8 3.4 0.0965 0.0051 96.5 5.3 – 228 61594 Isofenphos 0.849 0.0405 84.9 4.8 0.0759 0.0035 75.9 4.6 – 229 61604 Propetamphos 0.861 0.0524 86.1 6.1 0.0828 0.0025 82.8 3.0 – 231 61602 Tebupirimphos 0.844 0.0448 84.4 5.3 0.0741 0.0033 74.1 4.5 – 

28 82662 Dimethoate 0.292 0.0416 29.2 14.3 0.0515 0.0120 51.5 23.3 E 30 61610 Tribuphos 0.400 0.0468 40.0 11.7 0.0328 0.0038 32.8 11.7 E 
34 Determination of Moderate-Use Pesticides and Selected Degradates in Water 

 by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry Table 6. Bias and variability data from eight reagent-water samples fortified with parent pesticide analytes at high (1.0 microgram per liter) and low (0.1 microgram per liter) concentrations—Continued High Low Rank P-Code Short name Median conc. (μg/L) F-pseu (μg/L) Median recovery (percent) Rel F-pseu (percent) Median conc. (μg/L) F-pseu (μg/L) Median recovery (percent) Rel F-pseu (percent) Remark code 71 34357 beta-Endosulfan 0.815 0.0194 81.5 2.4 0.0857 0.0033 85.7 3.8 E 76 61606 Tefluthrin 0.215 0.0367 21.5 17.1 0.0167 0.0022 16.7 13.4 E 83 38454 Dicrotophos 0.135 0.0249 13.5 18.5 0.0147 0.0035 14.7 23.8 E 93 61593 Iprodione 0.608 0.0265 60.8 4.4 0.0455 0.0024 45.5 5.4 E 102 61595 Cyhalothrin 0.194 0.0304 19.4 15.7 0.0091 0.0011 9.1 12.3 E 114 61586 Cypermethrin 0.270 0.0337 27.0 12.5 0.0307 0.0066 30.7 21.6 E 115 38716 Sulprofos 0.719 0.0330 71.9 4.6 0.0596 0.0045 59.6 7.5 E 125 61601 Phosmet1 0.586 0.0420 58.6 7.2 -- -- -- -- E 129 61585 Cyfluthrin 0.265 0.0330 26.5 12.5 0.0310 0.0061 31.0 19.7 E 131 61580 Bifenthrin 0.262 0.0555 26.2 21.2 0.0132 0.0023 13.2 17.2 E 230 61605 Sulfotepp 0.960 0.0293 96.0 3.0 0.0851 0.0023 85.1 2.8 E 232 61607 Temephos 0.283 0.0499 28.3 17.7 0.0371 0.0040 37.1 10.7 E Degradates 1002 61615 2-[2-Ethyl-6-m_panol -- -- -- -- -- -- -- -- – 1007 61618 2-Chloro-2,6-d_ilide -- -- -- -- -- -- -- -- – 1008 61665 4-(Hydroxymeth_halin -- -- -- -- -- -- -- -- – 1016 61674 Terbufos-O-ana_lfone -- -- -- -- -- -- -- -- – 1033 61625 3,4-Dichloroaniline -- -- -- -- -- -- -- -- – 1043 61629 3-Phenoxybenzy_cohol -- -- -- -- -- -- -- -- – 1044 79842 c-Methyl-3-(2,_ylate 0.015 0.0016 1.5 10.6 0.0057 0.0009 5.7 16.3 – 1044 79843 t-Methyl-3-(2,_ylate 0.010 0.0007 1.0 7.5 0.0070 0.0003 7.0 3.7 – 

1049 61663 Paraoxon-ethyl -- -- -- -- -- -- -- -- – 1060 61652 Malaoxon -- -- -- -- -- -- -- -- – 1062 61637 2-(4-tert-buty_xanol -- -- -- -- -- -- -- -- – 1067 61640 Disulfoton sulfone -- -- -- -- -- -- -- -- – 1067 61641 Disulfoton sulfoxide -- -- -- -- -- -- -- -- – 1071 61590 Endosulfan sulfate -- -- -- -- -- -- -- -- – 1071 61642 Endosulfan ether 0.007 0.0011 0.7 15.8 0.0033 0.0007 3.3 21.1 – 1076 61672 Tefluthrin met_2912] -- -- -- -- -- -- -- -- – 
Final Method Validation 35 

Table 6. Bias and variability data from eight reagent-water samples fortified with parent pesticide analytes at high (1.0 microgram per liter) 

and low (0.1 microgram per liter) concentrations—Continued 

High Low 

Rank P-Code Short name Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent)

Rel 

F-pseu 

(percent) 

 Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent) 

Rel 

F-pseu 

(percent) 

Remark

code 

1093 61627 3,5-Dichloroaniline -- -- -- -- -- -- -- -- – 1099 61614 2,5-Dichloroaniline -- -- -- -- -- -- -- -- – 1124 61660 O-Ethyl-O-meth_ioate -- -- -- -- 0.0029 0.0003 2.9 10.0 – 1126 61645 Fenamiphos sulfone -- -- -- -- -- -- -- -- – 1231 61669 Tebupirimphos,_logue -- -- -- -- -- -- -- -- – 1002 61620 2-Ethyl-6-meth_iline -- -- -- -- -- -- -- -- E 1012 61636 Chlorpyrifos, _nalog -- -- -- -- -- -- -- -- E 1013 61617 2-Amino-N-isop_amide -- -- -- -- -- -- -- -- E 1014 61664 Paraoxon-methyl -- -- -- -- -- -- -- -- E 1015 61633 4-Chloro-2-met_henol -- -- -- -- -- -- -- -- E 1024 61630 3-Trifluoromet_iline -- -- -- -- -- -- -- -- E 1032 49295 1-Naphthol -- -- -- -- -- -- -- -- E 1032 61611 1,4-Naphthaquinone -- -- -- -- -- -- E 1034 61666 Phorate oxon -- -- -- -- -- -- -- -- E 1053 61635 Azinphos-methyl-oxon -- -- -- -- -- -- -- -- E 1054 61649 Fonofos, oxyge_nalog -- -- -- -- -- -- -- -- E 1076 61671 Tefluthrin met_9364] -- -- -- -- -- -- -- -- E 1101 61631 4,4'-Dichlorob_enone -- -- -- -- -- -- -- -- E 1105 61634 4-Chlorobenzyl_lfone -- -- -- -- -- -- -- -- E 1125 61668 Phosmet oxon -- -- -- -- -- -- -- -- E 1126 61646 Fenamiphos sulfoxide -- -- -- -- -- -- -- -- E 1134 61644 Ethion monoxon -- -- -- -- 0.0101 0.0009 10.1 9.3 E 1153 38775 Dichlorvos -- -- -- -- -- -- -- -- E 1227 61647 Fenthion sulfoxide 0.014 0.0009 1.4 6.2 0.0048 0.0011 4.8 22.8 E 

Surrogates -- -- -- -- -- -- -- -- – 

 99223 Diazinon-d10, _ogate 0.755 0.0169 75.5 2.2 0.0996 0.0021 99.6 2.1 – 

 99224 alpha-HCH-d6, _ogate 0.953 0.0457 95.3 4.8 0.0859 0.0033 85.9 3.8 – 

1Phosmet was not included in low concentration recovery experiments.
36 Determination of Moderate-Use Pesticides and Selected Degradates in Water 

 by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry Table 7. Bias and variability data from eight reagent-water samples fortified with degradates at high (1.0 microgram per liter) and low (0.1 microgram per liter) concentrations [Analytes are sorted by remark code and then by rank. Rank, national application and use rank of pesticide; P-Code, National Water Information System parameter code; Median conc., median observed concentration; μg/L, microgram per liter; F-pseu, F-pseudosigma (interquartile range/1.349); Rel F-pseu, relative F-pseudosigma; –, not applicable; E, estimated remark code] High Low Rank P-Code Short name Median conc. (μg/L) F-pseu (μg/L) Median recovery (percent) Rel F-pseu (percent) Median conc. (μg/L) F-pseu (μg/L) Median recovery (percent) Rel F-pseu (percent) Remark code Degradates 1002 61615 2-[2-Ethyl-6-m_panol 1.009 0.0988 100.9 9.8 0.0808 0.0053 80.8 6.6 – 1007 61618 2-Chloro-2,6-d_ilide 1.054 0.0439 105.4 4.2 0.0938 0.0018 93.8 1.9 – 1008 61665 4-(Hydroxymeth_halin 1.051 0.1364 105.1 13.0 0.0834 0.0077 83.4 9.3 – 1016 61674 Terbufos-O-ana_lfone 0.954 0.0797 95.4 8.4 0.0774 0.0071 77.4 9.1 – 1033 61625 3,4-Dichloroaniline 0.947 0.1165 94.7 12.3 0.0863 0.0084 86.3 9.7 – 1043 61629 3-Phenoxybenzy_cohol 1.132 0.0972 113.2 8.6 0.0718 0.0024 71.8 3.3 – 1044 79842 c-Methyl-3-(2,_ylate 0.862 0.0574 86.2 6.7 0.0846 0.0028 84.6 3.3 – 1044 79843 t-Methyl-3-(2,_ylate 0.927 0.0512 92.7 5.5 0.0891 0.0040 89.1 4.5 – 1049 61663 Paraoxon-ethyl 1 1.198 0.3089 119.8 25.8 0.0872 0.0028 87.2 3.3 – 1060 61652 Malaoxon 1.009 0.0727 100.9 7.2 0.0919 0.0052 91.9 5.7 – 1062 61637 2-(4-tert-buty_xanol 1.060 0.0547 106.0 5.2 0.0800 0.0057 80.0 7.1 – 1067 61640 Disulfoton sulfone 0.923 0.0734 92.3 8.0 0.0783 0.0033 78.3 4.2 – 1071 61590 Endosulfan sulfate 1 0.865 0.0209 86.5 2.4 0.0919 0.0032 91.9 3.5 – 1071 61642 Endosulfan ether 1.088 0.0430 108.8 4.0 0.1018 0.0027 101.8 2.6 – 1076 61672 Tefluthrin met_2912] 0.653 0.0898 65.3 13.7 0.0601 0.0024 60.1 4.0 – 1093 61627 3,5-Dichloroaniline 1.081 0.1030 108.1 9.5 0.0965 0.0064 96.5 6.6 – 1099 61614 2,5-Dichloroaniline 0.986 0.1050 98.6 10.7 0.0856 0.0050 85.6 5.9 – 

1124 61660 O-Ethyl-O-meth_ioate 0.954 0.0856 95.4 9.0 0.0852 0.0047 85.2 5.6 – 1126 61645 Fenamiphos sulfone 0.861 0.1068 86.1 12.4 0.0637 0.0053 63.7 8.3 – 

1231 61669 Tebupirimphos,_logue 0.900 0.0719 90.0 8.0 0.0722 0.0025 72.2 3.5 – 

1002 61620 2-Ethyl-6-meth_iline 1.090 0.0788 109.0 7.2 0.1014 0.0019 101.4 1.9 E 

1012 61636 Chlorpyrifos, _nalog 0.282 0.0466 28.2 16.5 0.0176 0.0051 17.6 28.7 E 1013 61617 2-Amino-N-isop_amide 0.675 0.0681 67.5 10.1 0.0589 0.0088 58.9 15.0 E 1014 61664 Paraoxon-methyl 0.852 0.0909 85.2 10.7 0.0695 0.0022 69.5 3.2 E 
Final Method Validation 37 

Table 7. Bias and variability data from eight reagent-water samples fortified with degradates at high (1.0 microgram per liter) and low (0.1 microgram per liter) concentrations—Continued 

High Low 

Rank P-Code Short name Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent) 

Rel 

F-pseu 

(percent) 

 Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent)

Rel 

F-pseu 

(percent)

Remark

code 

1015 61633 4-Chloro-2-met_henol 0.817 0.1319 81.7 16.1 0.0721 0.0098 72.1 13.7 E 1024 61630 3-Trifluoromet_iline 0.451 0.1181 45.1 26.2 0.0407 0.0030 40.7 7.5 E 1032 49295 1-Naphthol 0.136 0.0542 13.6 39.9 0.0255 0.0103 25.5 40.4 E 1032 61611 1,4-Naphthaquinone 0.211 0.1189 21.1 56.2 0.0335 0.0104 33.5 31.0 E 1034 61666 Phorate oxon 0.879 0.1341 87.9 15.2 0.0727 0.0059 72.7 8.1 E 1053 61635 Azinphos-methyl-oxon 0.919 0.0993 91.9 10.8 0.0575 0.0115 57.5 19.9 E 1054 61649 Fonofos, oxyge_nalog 0.839 0.0861 83.9 10.3 0.0709 0.0019 70.9 2.7 E 1067 61641 Disulfoton sulfoxide 1.417 0.0640 141.7 4.5 0.1318 0.0070 131.8 5.3 E 1076 61671 Tefluthrin met_9364] 0.491 0.0892 49.1 18.2 0.0451 0.0034 45.1 7.6 E 1101 61631 4,4'-Dichlorob_enone 0.900 0.0763 90.0 8.5 0.0697 0.0026 69.7 3.8 E 1105 61634 4-Chlorobenzyl_lfone 0.681 0.0671 68.1 9.8 0.0654 0.0073 65.4 11.2 E 1125 61668 Phosmet oxon 0.771 0.0593 77.1 7.7 0.0294 0.0102 29.4 34.8 E 1126 61646 Fenamiphos sulfoxide 0.197 0.0277 19.7 14.0 0.0251 0.0029 25.1 11.4 E 1134 61644 Ethion monoxon 0.645 0.0837 64.5 13.0 0.0452 0.0022 45.2 4.8 E 1153 38775 Dichlorvos1 0.673 0.0752 67.3 11.2 0.0803 0.0041 80.3 5.1 E 

1227 61647 Fenthion sulfoxide 0.823 0.1058 82.3 12.9 0.0785 0.0035 78.5 4.5 E 

Surrogates 

 99223 Diazinon-d10, _ogate 1.472 0.0466 147.2 3.2 0.1083 0.0051 108.3 4.7 – 

 99224 alpha-HCH-d6, _ogate 0.613 0.0487 61.3 7.9 0.0596 0.0028 59.6 4.7 – 

1Analyte was determined in parent fortification mixture.
38 Determination of Moderate-Use Pesticides and Selected Degradates in Water 

 by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry Table 8. Bias and variability data from eight surface-water samples fortified with parent pesticides and degradates at high (1.0 microgram per liter) and low (0.1 microgram per liter) concentrations [Analytes are separated into parent pesticides and degradate pesticides and sorted by remark code and then by rank. Surface water collected from Boulder Creek at 75th Street on June 3, 1999. Analysis of unfortified sample indicated no analytes greater than reporting levels. Rank, national application and use rank of pesticide; P-Code, National Water Information System parameter code; F-pseu, F-pseudosigma (interquartile range/1.349); Rel F-pseu, relative F- pseudosigma; μg/L, microgram per liter; –, not applicable; --, not analyzed; E, estimated remark code] High Low Rank P-Code Short name Median conc. (μg/L) F-pseu (μg/L) Median recovery (percent) Rel F-pseu (percent) Median conc. (μg/L) F-pseu (μg/L) Median recovery (percent) Rel F-pseu (percent) Remark code Parent pesticides 63 04036 Prometryn 0.410 0.3697 41.0 90.2 0.0786 0.0040 78.6 4.0 – 69 61603 Profenofos 0.768 0.0358 76.8 4.7 0.1041 0.0063 104.1 6.3 – 71 34362 alpha-Endosulfan 0.796 0.0199 79.6 2.5 0.0962 0.0117 96.2 11.7 – 75 61596 Metalaxyl 0.952 0.0414 95.2 4.3 0.0910 0.0040 91.0 4.0 – 106 61600 Oxyfluorfen 0.675 0.0839 67.5 12.4 0.0927 0.0086 92.7 8.6 – 108 79846 cis-Propiconazole 0.239 0.2567 23.9 107.4 0.1063 0.0068 106.3 6.8 – 110 79847 trans-Propiconazole 0.470 0.2901 47.0 61.7 0.1089 0.0047 108.9 4.7 – 121 61599 Myclobutanil 0.798 0.0358 79.8 4.5 0.1034 0.0031 103.4 3.1 – 126 61591 Fenamiphos 0.796 0.0404 79.6 5.1 0.1024 0.0051 102.4 5.1 – 127 04025 Hexazinone 0.615 0.0818 61.5 13.3 0.0981 0.0030 98.1 3.0 – 128 04031 Cycloate 0.844 0.0598 84.4 7.1 0.1045 0.0069 104.5 6.9 – 132 61598 Methidathion 0.849 0.0496 84.9 5.8 0.1102 0.0038 110.2 3.8 – 134 82346 Ethion 0.496 0.0193 49.6 3.9 0.0800 0.0045 80.0 4.5 – 211 79844 (E)-Dimethomorph 0.846 0.0412 84.6 4.9 0.1026 0.0043 102.6 4.3 – 212 79845 (Z)-Dimethomorph 0.838 0.0248 83.8 3.0 0.1091 0.0060 109.1 6.0 – 220 04022 Terbuthylazine1 -- -- -- -- -- -- -- -- – 225 61592 Flumetralin 0.499 0.0939 49.9 18.8 0.0918 0.0056 91.8 5.6 – 

227 38801 Fenthion 0.934 0.0501 93.4 5.4 0.0697 0.0042 69.7 4.2 – 228 61594 Isofenphos 0.883 0.0426 88.3 4.8 0.0921 0.0043 92.1 4.3 – 229 61604 Propetamphos 0.863 0.0396 86.3 4.6 0.0966 0.0072 96.6 7.2 – 231 61602 Tebupirimphos 0.767 0.0219 76.7 2.9 0.0802 0.0049 80.2 4.9 – 

28 82662 Dimethoate 0.450 0.0715 45.0 15.9 0.0413 0.0011 41.3 1.1 E 30 61610 Tribuphos 0.451 0.0265 45.1 5.9 0.0825 0.0041 82.5 4.1 E 71 34357 beta-Endosulfan 0.703 0.0362 70.3 5.1 0.1047 0.0071 104.7 7.1 E 

76 61606 Tefluthrin 0.173 0.0135 17.3 7.8 0.0414 0.0038 41.4 3.8 E 
Final Method Validation 39 

Table 8. Bias and variability data from eight surface-water samples fortified with parent pesticides and degradates at high (1.0 microgram per liter) and low (0.1 microgram per liter) concentrations—Continued 

High Low 

Rank P-Code Short name Median 

conc. 

(μg/L) 

F-pseu

(μg/L) 

Median 

recovery

(percent) 

Rel 

F-pseu 

(percent) 

 Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent) 

Rel 

F-pseu 

(percent)

Remark

code 

83 38454 Dicrotophos 0.164 0.0548 16.4 33.5 0.0338 0.0026 33.8 2.6 E 93 61593 Iprodione 0.690 0.0239 69.0 3.5 0.1116 0.0117 111.6 11.7 E 

102 61595 Cyhalothrin 0.160 0.0170 16.0 10.6 0.0454 0.0037 45.4 3.7 E 114 61586 Cypermethrin 0.223 0.0195 22.3 8.7 0.0787 0.0093 78.7 9.3 E 115 38716 Sulprofos 0.476 0.0343 47.6 7.2 0.0792 0.0046 79.2 4.6 E 125 61601 Phosmet 0.622 0.0490 62.2 7.9 0.1058 0.0035 105.8 3.5 E 129 61585 Cyfluthrin 0.214 0.0092 21.4 4.3 0.0773 0.0026 77.3 2.6 E 131 61580 Bifenthrin 0.144 0.0108 14.4 7.5 0.0506 0.0041 50.6 4.1 E 230 61605 Sulfotepp 0.734 0.0380 73.4 5.2 0.0651 0.0053 65.1 5.3 E 232 61607 Temephos 0.217 0.0146 21.7 6.7 0.1425 0.0097 142.5 9.7 E 

Degradates 

1002 61615 2-[2-Ethyl-6-m_panol 0.871 0.0335 87.1 3.8 0.1055 0.0087 105.5 8.7 – 1007 61618 2-Chloro-2,6-d_ilide 0.903 0.0638 90.3 7.1 0.0980 0.0052 98.0 5.2 – 1008 61665 4-(Hydroxymeth_halin 0.993 0.0161 99.3 1.6 0.1329 0.0097 132.9 9.7 – 1016 61674 Terbufos-O-ana_lfone 0.861 0.0410 86.1 4.8 0.0923 0.0053 92.3 5.3 – 1033 61625 3,4-Dichloroaniline 0.926 0.0359 92.6 3.9 0.0765 0.0023 76.5 2.3 – 1043 61629 3-Phenoxybenzy_cohol 0.827 0.0430 82.7 5.2 0.0896 0.0073 89.6 7.3 – 1044 79842 c-Methyl-3-(2,_ylate 0.788 0.0185 78.8 2.4 0.0955 0.0054 95.5 5.4 – 1044 79843 t-Methyl-3-(2,_ylate 0.805 0.0239 80.5 3.0 0.0905 0.0074 90.5 7.4 – 

1049 61663 Paraoxon-ethyl 0.922 0.0337 92.2 3.7 0.1012 0.0074 101.2 7.4 – 

1060 61652 Malaoxon 0.873 0.0345 87.3 3.9 0.1064 0.0071 106.4 7.1 – 1062 61637 2-(4-tert-buty_xanol 0.864 0.0433 86.4 5.0 0.1042 0.0087 104.2 8.7 – 1067 61640 Disulfoton sulfone 0.869 0.0416 86.9 4.8 0.1045 0.0035 104.5 3.5 – 1071 61590 Endosulfan sulfate 0.761 0.0237 76.1 3.1 0.0915 0.0079 91.5 7.9 – 1071 61642 Endosulfan ether 0.826 0.0264 82.6 3.2 0.0805 0.0052 80.5 5.2 – 1076 61672 Tefluthrin met_2912] 0.327 0.0363 32.7 11.1 0.0675 0.0068 67.5 6.8 – 1093 61627 3,5-Dichloroaniline 0.923 0.0276 92.3 3.0 0.0913 0.0051 91.3 5.1 – 1099 61614 2,5-Dichloroaniline 0.841 0.0154 84.1 1.8 0.0819 0.0043 81.9 4.3 – 1124 61660 O-Ethyl-O-meth_ioate 0.856 0.0298 85.6 3.5 0.0978 0.0058 97.8 5.8 – 1126 61645 Fenamiphos sulfone 0.788 0.0353 78.8 4.5 0.0955 0.0047 95.5 4.7 – 
40 Determination of Moderate-Use Pesticides and Selected Degradates in Water 

 by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry Table 8. Bias and variability data from eight surface-water samples fortified with parent pesticides and degradates at high (1.0 microgram per liter) and low (0.1 microgram per liter) concentrations—Continued High Low Rank P-Code Short name Median conc. (μg/L) F-pseu (μg/L) Median recovery (percent) Rel F-pseu (percent) Median conc. (μg/L) F-pseu (μg/L) Median recovery (percent) Rel F-pseu (percent) Remark code 1231 61669 Tebupirimphos,_logue 0.832 0.0376 83.2 4.5 0.0766 0.0051 76.6 5.1 – 1002 61620 2-Ethyl-6-meth_iline 0.786 0.0422 78.6 5.4 0.1170 0.0049 117.0 4.9 E 1012 61636 Chlorpyrifos, _nalog 0.780 0.0296 78.0 3.8 0.0496 0.0032 49.6 3.2 E 1013 61617 2-Amino-N-isop_amide 0.689 0.0878 68.9 12.8 0.0476 0.0019 47.6 1.9 E 1014 61664 Paraoxon-methyl 0.884 0.0501 88.4 5.7 0.1047 0.0032 104.7 3.2 E 1015 61633 4-Chloro-2-met_henol 0.814 0.0515 81.4 6.3 0.0693 0.0034 69.3 3.4 E 1024 61630 3-Trifluoromet_iline 0.733 0.0928 73.3 12.7 0.0432 0.0011 43.2 1.1 E 1032 49295 1-Naphthol1 -- -- -- -- -- -- -- -- E 1032 61611 1,4-Naphthaquinone1 -- -- -- -- 0.0733 0.0042 73.3 4.2 E 1034 61666 Phorate oxon 0.862 0.0463 86.2 5.4 0.0848 0.0049 84.8 4.9 E 1053 61635 Azinphos-methyl-oxon 0.875 0.0470 87.5 5.4 0.1316 0.0004 131.6 0.4 E 1054 61649 Fonofos, oxyge_nalog 0.774 0.0463 77.4 6.0 0.0922 0.0065 92.2 6.5 E 1067 61641 Disulfoton sulfoxide 0.966 0.0507 96.6 5.3 0.1051 0.0069 105.1 6.9 E 1076 61671 Tefluthrin met_9364] 0.217 0.0143 21.7 6.6 0.0404 0.0052 40.4 5.2 E 1101 61631 4,4'-Dichlorob_enone 0.858 0.0305 85.8 3.6 0.1035 0.0079 103.5 7.9 E 1105 61634 4-Chlorobenzyl_lfone 0.684 0.0919 68.4 13.4 0.0538 0.0040 53.8 4.0 E 1125 61668 Phosmet oxon 0.601 0.0504 60.1 8.4 0.1188 0.0021 118.8 2.1 E 1126 61646 Fenamiphos sulfoxide1 -- -- -- -- 0.0552 0.0120 55.2 12.0 E 1134 61644 Ethion monoxon 0.771 0.0296 77.1 3.8 0.1007 0.0045 100.7 4.5 E 1153 38775 Dichlorvos 0.638 0.0349 63.8 5.5 0.0444 0.0023 44.4 2.3 E 1227 61647 Fenthion sulfoxide 0.775 0.0336 77.5 4.3 0.0965 0.0038 96.5 3.8 E 

Surrogates 

 99223 Diazinond10, _ogate 1.209 0.0290 120.9 2.4 0.0781 0.0023 78.1 2.3 – 

 99224 alpha-HCHd6, _ogate 0.865 0.1916 86.5 22.1 0.0980 0.0047 98.0 4.7 – 

1Terbuthylazine, 1-naphthol, 1,4-naphthaquinone, and fenamiphos sulfoxide not included in fortification mixture. 
Final Method Validation 41 

Table 9. Bias and variability data from eight ground-water samples fortified with parent pesticides and degradates at high (1.0 microgram per liter) 

and low (0.1 microgram per liter) concentrations [Analytes are separated into parent pesticides and degradate pesticides and sorted by remark code and then by rank. Ground water collected in northeast Denver on June 3, 1999. Analysis of unfortified sample indicated no analytes greater than reporting limits. Rank, national application and use rank of pesticide; P-Code, National Water Information System parameter code; μg/L, microgram per liter; F-pseu, F-pseudosigma (interquartile range/1.349); Rel Fpseu, relative F-pseudosigma; –, not applicable; --, not analyzed; E, estimated remark code] 

High Low 

Rank P-Code Short name Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent)

Rel 

F-pseu 

(percent) 

 Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent) 

Rel 

F-pseu 

(percent) 

Remark

code 

Parent pesticides 

63 04036 Prometryn 1.010 0.031 101.0 3.1 0.0821 0.0057 82.1 6.9 – 69 61603 Profenofos 0.782 0.037 78.2 4.8 0.0926 0.0086 92.6 9.3 – 

71 34362 alpha-Endosulfan 0.818 0.034 81.8 4.2 0.0951 0.0056 95.1 5.9 – 

75 61596 Metalaxyl 0.952 0.027 95.2 2.9 0.0910 0.0047 91.0 5.2 – 

106 61600 Oxyfluorfen 0.849 0.038 84.9 4.5 0.0917 0.0051 91.7 5.6 – 108 79846 cis-Propiconazole 0.604 0.016 60.4 2.6 0.1144 0.0076 114.4 6.7 – 

110 79847 trans-Propiconazole 0.877 0.034 87.7 3.8 0.1102 0.0109 110.2 9.9 – 

121 61599 Myclobutanil 0.881 0.029 88.1 3.3 0.1069 0.0040 106.9 3.7 – 

126 61591 Fenamiphos 0.771 0.024 77.1 3.2 0.1048 0.0098 104.8 9.4 – 

127 04025 Hexazinone 0.645 0.026 64.5 4.1 0.0902 0.0103 90.2 11.4 – 128 04031 Cycloate 0.942 0.070 94.2 7.4 0.0950 0.0056 95.0 5.9 – 132 61598 Methidathion 0.848 0.012 84.8 1.5 0.1033 0.0055 103.3 5.3 – 134 82346 Ethion 0.637 0.047 63.7 7.3 0.0850 0.0042 85.0 4.9 – 211 79844 (E)-Dimethomorph 0.851 0.031 85.1 3.6 0.0958 0.0042 95.8 4.3 – 212 79845 (Z)-Dimethomorph 0.844 0.032 84.4 3.8 0.1006 0.0041 100.6 4.1 – 220 04022 Terbuthylazine1 -- -- -- -- -- -- -- -- – 

225 61592 Flumetralin 0.973 0.092 97.3 9.5 0.0949 0.0062 94.9 6.6 – 

227 38801 Fenthion 0.993 0.022 99.3 2.2 0.0789 0.0050 78.9 6.3 – 228 61594 Isofenphos 0.948 0.033 94.8 3.4 0.0918 0.0043 91.8 4.7 – 229 61604 Propetamphos 0.876 0.032 87.6 3.7 0.0908 0.0040 90.8 4.4 – 231 61602 Tebupirimphos 0.841 0.025 84.1 3.0 0.0787 0.0050 78.7 6.3 – 

28 82662 Dimethoate 0.328 0.007 32.8 2.1 0.0447 0.0033 44.7 7.4 E 30 61610 Tribuphos 0.541 0.057 54.1 10.5 0.0842 0.0089 84.2 10.6 E 71 34357 beta-Endosulfan 0.775 0.043 77.5 5.5 0.0982 0.0125 98.2 12.7 E 

76 61606 Tefluthrin 0.339 0.041 33.9 12.2 0.0461 0.0051 46.1 11.1 E 
42 Determination of Moderate-Use Pesticides and Selected Degradates in Water 

 by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry Table 9. Bias and variability data from eight ground-water samples fortified with parent pesticides and degradates at high (1.0 microgram per liter) and low (0.1 microgram per liter) concentrations—Continued High Low Rank P-Code Short name Median conc. (μg/L) F-pseu (μg/L) Median recovery

(percent)

Rel 

F-pseu 

(percent) 

 Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent) 

Rel 

F-pseu 

(percent)

Remark 

code 

83 38454 Dicrotophos 0.147 0.011 14.7 7.4 0.0186 0.0052 18.6 28.3 E 93 61593 Iprodione 0.708 0.049 70.8 6.9 0.1051 0.0128 105.1 12.2 E 

102 61595 Cyhalothrin 0.361 0.034 36.1 9.4 0.0479 0.0050 47.9 10.5 E 114 61586 Cypermethrin 0.435 0.033 43.5 7.6 0.0767 0.0067 76.7 8.8 E 115 38716 Sulprofos 0.622 0.047 62.2 7.5 0.1014 0.0079 101.4 7.8 E 125 61601 Phosmet 0.771 0.035 77.1 4.6 0.0869 0.0074 86.9 8.6 E 129 61585 Cyfluthrin 0.415 0.035 41.5 8.5 0.0749 0.0032 74.9 4.3 E 131 61580 Bifenthrin 0.373 0.041 37.3 11.0 0.0575 0.0055 57.5 9.6 E 230 61605 Sulfotepp 0.844 0.019 84.4 2.3 0.0783 0.0067 78.3 8.5 E 232 61607 Temephos 0.471 0.026 47.1 5.5 0.1296 0.0101 129.6 7.8 E 

Degradates 

1002 61615 2-[2-Ethyl-6-m_panol 0.838 0.016 83.8 2.0 0.1030 0.0049 103.0 4.8 – 1007 61618 2-Chloro-2,6-d_ilide 0.837 0.072 83.7 8.6 0.0934 0.0067 93.4 7.1 – 

1008 61665 4-(Hydroxymeth_halin 0.993 0.010 99.3 1.0 0.1159 0.0055 115.9 4.8 – 1016 61674 Terbufos-O-ana_lfone 0.820 0.016 82.0 1.9 0.0879 0.0108 87.9 12.3 – 1033 61625 3,4-Dichloroaniline 0.836 0.020 83.6 2.4 0.0853 0.0046 85.3 5.4 – 1043 61629 3-Phenoxybenzy_cohol 0.804 0.019 80.4 2.3 0.0848 0.0059 84.8 6.9 – 1044 79842 c-Methyl-3-(2,_ylate 0.834 0.017 83.4 2.0 0.0893 0.0063 89.3 7.1 – 1044 79843 t-Methyl-3-(2,_ylate 0.832 0.018 83.2 2.2 0.0891 0.0078 89.1 8.7 – 

1049 61663 Paraoxon-ethyl 0.908 0.033 90.8 3.7 0.0894 0.0114 89.4 12.8 – 

1060 61652 Malaoxon 0.809 0.023 80.9 2.9 0.0933 0.0089 93.3 9.5 – 

1062 61637 2-(4-tert-buty_xanol 0.875 0.027 87.5 3.1 0.0915 0.0081 91.5 8.9 – 1067 61640 Disulfoton sulfone 0.850 0.024 85.0 2.8 0.1059 0.0062 105.9 5.8 – 1071 61590 Endosulfan sulfate 0.809 0.036 80.9 4.4 0.0892 0.0045 89.2 5.1 – 1071 61642 Endosulfan ether 0.846 0.023 84.6 2.7 0.0794 0.0055 79.4 6.9 – 1076 61672 Tefluthrin met_2912] 0.500 0.028 50.0 5.5 0.0641 0.0048 64.1 7.5 – 1093 61627 3,5-Dichloroaniline 0.881 0.030 88.1 3.4 0.0919 0.0067 91.9 7.3 – 1099 61614 2,5-Dichloroaniline 0.725 0.031 72.5 4.3 0.0810 0.0060 81.0 7.4 – 1124 61660 O-Ethyl-O-meth_ioate 0.807 0.024 80.7 2.9 0.0889 0.0065 88.9 7.3 – 1126 61645 Fenamiphos sulfone 0.813 0.008 81.3 1.0 0.0886 0.0048 88.6 5.4 – 
Final Method Validation 43 

Table 9. Bias and variability data from eight ground-water samples fortified with parent pesticides and degradates at high (1.0 microgram per liter) 

and low (0.1 microgram per liter) concentrations—Continued 

High Low 

Rank P-Code Short name Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent)

Rel 

F-pseu 

(percent) 

 Median 

conc. 

(μg/L) 

F-pseu 

(μg/L) 

Median 

recovery

(percent) 

Rel 

F-pseu 

(percent)

Remark 

code 

1231 61669 Tebupirimphos,_logue 0.840 0.018 84.0 2.1 0.0739 0.0061 73.9 8.2 – 1002 61620 2-Ethyl-6-meth_iline 0.772 0.008 77.2 1.0 0.1034 0.0082 103.4 8.0 E 1012 61636 Chlorpyrifos, _nalog 0.662 0.072 66.2 10.9 0.0440 0.0088 44.0 19.9 E 1013 61617 2-Amino-N-isop_amide 0.548 0.010 54.8 1.8 0.0588 0.0031 58.8 5.2 E 1014 61664 Paraoxon-methyl 0.817 0.058 81.7 7.1 0.0844 0.0086 84.4 10.2 E 1015 61633 4-Chloro-2-met_henol 0.619 0.017 61.9 2.7 0.0681 0.0049 68.1 7.3 E 1024 61630 3-Trifluoromet_iline 0.466 0.023 46.6 4.9 0.0518 0.0033 51.8 6.3 E 1032 49295 1-Naphthol 0.341 0.083 34.1 24.4 0.0063 0.0018 6.3 28.9 E 1032 61611 1,4-Naphthaquinone1 -- -- -- -- 0.0781 0.0065 78.1 8.3 E 

1034 61666 Phorate oxon 0.842 0.016 84.2 1.9 0.0802 0.0079 80.2 9.8 E 1053 61635 Azinphos-methyl-oxon 0.810 0.039 81.0 4.8 0.1258 0.0058 125.8 4.6 E 1054 61649 Fonofos, oxyge_nalog 0.694 0.038 69.4 5.5 0.0776 0.0067 77.6 8.6 E 1067 61641 Disulfoton sulfoxide 0.960 0.029 96.0 3.0 0.0996 0.0056 99.6 5.6 E 1076 61671 Tefluthrin met_9364] 0.394 0.044 39.4 11.2 0.0432 0.0046 43.2 10.7 E 1101 61631 4,4'-Dichlorob_enone 0.844 0.038 84.4 4.5 0.0928 0.0073 92.8 7.9 E 1105 61634 4-Chlorobenzyl_lfone 0.506 0.006 50.6 1.1 0.0552 0.0023 55.2 4.2 E 1125 61668 Phosmet oxon 0.735 0.034 73.5 4.7 0.0999 0.0083 99.9 8.3 E 1126 61646 Fenamiphos sulfoxide1 -- -- -- -- 0.0174 0.0010 17.4 5.9 E 

1134 61644 Ethion monoxon 0.811 0.034 81.1 4.2 0.1002 0.0043 100.2 4.3 E 1153 38775 Dichlorvos 0.451 0.040 45.1 8.8 0.0312 0.0083 31.2 26.5 E 1227 61647 Fenthion sulfoxide 0.750 0.022 75.0 3.0 0.0850 0.0061 85.0 7.2 E 

Surrogates 

 99223 Diazinon-d10, _ogate 1.238 0.028 123.8 2.3 0.0750 0.0030 75.0 4.0 – 

 99224 alpha-HCH-d6, _ogate 1.036 0.280 103.6 27.0 0.0941 0.0058 94.1 6.1 – 

1Terbuthylazine, 1,4-naphthaquinone, and fenamiphos sulfoxide not included in fortification mixture.
Method Detection Limits 

Short-term method detection limits 

(MDLs) for pesticides and pesticide

degradates were estimated by determining the

analytes in eight reagent-water samples 

fortified at concentrations of 0.015 μg/L for 

most analytes. The MDLs usually are 

calculated as about three standard deviations 

of the mean concentration (U.S. 

Environmental Protection Agency, 1997). For 

this report, the F-pseudosigma rather than the 

standard deviation was used to calculate the 

MDLs. 

( 1,1α  0.99)  n

MDL F t , (11) 

where F = F-pseudosigma of replicate 

analyses, in micrograms per 

 liter; 

 n = number of replicate samples; 

t = Student’s t-value for a one-tailed 

test appropriate for the 

99-percent confidence level 

 (1-α = 0.99) with n-1 degrees 

of freedom; and 

α = level of significance. 

For eight replicates and a 99-percent

confidence level, the value of t is 2.998. The 

phrase, short-term MDL, is used to 

differentiate these one-time and oneanalytical-instrument estimates from longterm MDLs (LT–MDLs) determined over a 

longer time and that use results from different 

analytical instruments (Childress and others, 

1999). Exercise caution in interpreting these 

MDLs and the preliminary LRLs because 

they are based on short-term studies, and for 

some of the analytes, the fortification level 

was greater than 2 to 5 times the MDL as

recommended in the procedure (U.S. 

Environmental Protection Agency, 1997). 

Some analytes that had low recovery or 

instrumental response were fortified at 

successively higher concentrations (0.025, 

0.075, and 0.1 μg/L). Samples were analyzed 

on one instrument. The preliminary estimated 

MDLs ranged from 0.001 to 0.7 μg/L, with a 

median MDL of 0.002 μg/L for all analytes 

(table 10). More than 80 percent of the 

analytes had MDLs less than 0.01 μg/L. 

The LRLs are usually calculated as at

least twice the LT–MDLs (Childress and 

others, 1999). Because of the limitations of 

the short-term MDL noted above, preliminary

LRLs calculated using short-term MDLs were, 

in some cases, much lower than the lowest 

calibration standard that can be measured. 

Recently, the LRL calculation has been 

modified to include the bias introduced by low 

analyte recovery by calculating the LRL as 

twice the MDLs divided by the median 

recovery (expressed as a fraction) (Foreman 

and others, 2001). This new calculation 

resulted in preliminary LRLs for this method 

that were consistent with analysis of low 

calibration standards for most analytes (table

10). Eight analytes had calculated preliminary

LRLs that were too low for reliable detection 

(greater than the maximum 1 percent false

negative error rate; Childress and others, 

1999). Therefore, the concentration of the 

lowest calibration standard that could be 

reliably detected was used instead as an 

estimate of the preliminary LRL for these

analytes (shown in bold in table 10). The 

preliminary LRLs range from 0.003 to 0.267 

μg/L for most analytes (table 10). 

 Data Analysis 

The data summaries presented in tables 

6 through 10 use nonparametric equivalents 

of the more commonly used summary

statistics. For a description of the data, the 

median has been used rather than the 

arithmetic mean or average. Similarly, for the

dispersion or spread of the data, the 

44 Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry
Table 10. Method detection limits and preliminary laboratory reporting levels for pesticides and pesticide 

degradates calculated from determination of the analytes in eight reagent-water samples fortified at 

concentrations from 0.015 to 0.1 microgram per liter

[Analytes are separated into parent pesticides and degradates and sorted by remark code and then by rank. Analyses performed 

on one instrument. Rank, national application and use rank of pesticide; P-Code, National Water Information System

parameter code; μg/L , microgram per liter; Median conc., median concentration; F-pseu, F-pseudosigma; Rel F-pseu, relative 

F-pseudosigma; MDL, method detection limit; LRL, laboratory reporting level; bold numbers are estimated LRLs based on

lowest calibration standard observed; –, not applicable; E, estimated qualifier remark] 

Rank P-Code Short name

Fortification

level 

(μg/L) 

Median

conc. 

(μg/L) 

F-pseu

(μg/L) 

Median

recovery

(percent)

Rel 

F-pseu

(percent)

MDL

(μg/L) 

Preliminary

LRL 

(μg/L) 

Remark

code

Parent pesticides 

63 04036 Prometryn 0.015 0.0112 0.00067 74.7 6.0 0.0020 0.0054 –

69 61603 Profenofos 0.015 0.0067 0.00044 44.7 6.6 0.0013 0.0059 –

71 34362 alpha-Endosulfan 0.015 0.0078 0.00041 52.3 5.2 0.0012 0.0047 –

75 61596 Metalaxyl 0.015 0.0123 0.00069 81.7 5.6 0.0021 0.0051 –

106 61600 Oxyfluorfen 0.015 0.0065 0.00053 43.6 8.2 0.0016 0.0073 –

108 79846 cis-Propiconazole 0.015 0.0056 0.00021 37.4 3.8 0.0006 0.008 – 

110 79847 trans-Propiconazole 0.015 0.0030 0.00044 19.9 14.8 0.0013 0.0133 –

121 61599 Myclobutanil 0.015 0.0056 0.00037 37.4 6.6 0.0011 0.008 – 

126 61591 Fenamiphos 0.1 0.1010 0.00489 101.0 4.8 0.0154 0.0290 –

127 04025 Hexazinone 0.025 0.0079 0.00068 31.6 8.6 0.0020 0.0129 –

128 04031 Cycloate 0.015 0.0133 0.00070 88.7 5.3 0.0021 0.0047 –

132 61598 Methidathion 0.015 0.0068 0.00044 45.1 6.5 0.0013 0.0058 –

134 82346 Ethion 0.015 0.0059 0.00026 39.4 4.4 0.0008 0.0040 –

211 79844 (E)-Dimethomorph 0.075 0.0126 0.00057 16.8 4.6 0.0017 0.0203 –

212 79845 (Z)-Dimethomorph 0.075 0.0104 0.00106 13.9 10.2 0.0032 0.0457 –

220 04022 Terbuthylazine 0.015 0.0132 0.00150 88.0 11.4 0.0045 0.0102 –

225 61592 Flumetralin 0.015 0.0053 0.00018 35.1 3.4 0.0005 0.004 – 

227 38801 Fenthion 0.015 0.0064 0.00110 42.8 17.1 0.0033 0.0154 –

228 61594 Isofenphos 0.015 0.0100 0.00038 66.9 3.8 0.0011 0.0034 –

229 61604 Propetamphos 0.015 0.0101 0.00043 67.3 4.3 0.0013 0.0038 –

231 61602 Tebupirimphos 0.015 0.0110 0.00067 73.3 6.1 0.0020 0.0055 –

28 82662 Dimethoate 0.015 0.0052 0.00035 34.6 6.8 0.0011 0.0061 E

30 61610 Tribuphos 0.015 0.0054 0.00026 35.7 4.9 0.0008 0.0044 E

71 34357 beta-Endosulfan 0.025 0.0145 0.00137 58.0 9.5 0.0041 0.0142 E

76 61606 Tefluthrin 0.015 0.0048 0.00041 31.9 8.6 0.0012 0.0077 E

83 38454 Dicrotophos 0.1 0.0377 0.00530 37.7 14.1 0.0167 0.0843 E

93 61593 Iprodione 0.1 0.4120 0.23721 412.0 57.6 0.7456 1.4223 E

102 61595 Cyhalothrin 0.025 0.0049 0.00029 19.6 5.9 0.0009 0.0089 E

114 61586 Cypermethrin 0.025 0.0064 0.00037 25.8 5.8 0.0011 0.0086 E

115 38716 Sulprofos 0.015 0.0039 0.00067 26.0 17.3 0.0020 0.0155 E

125 61601 Phosmet 0.025 0.0055 0.00029 22.1 5.3 0.0009 0.0079 E

129 61585 Cyfluthrin 0.025 0.0104 0.00019 41.6 1.8 0.0006 0.008 E 

131 61580 Bifenthrin 0.015 0.0038 0.00022 25.1 6.0 0.0007 0.0053 E

230 61605 Sulfotepp 0.015 0.0106 0.00030 70.7 2.8 0.0009 0.0025 E

232 61607 Temephos1 0.1 0.0339 0.01509 33.9 44.5 0.0361 0.2669 E

Final Method Validation 45
Table 10. Method detection limits and preliminary laboratory reporting levels for pesticides and pesticide 

degradates calculated from determination of the analytes in eight reagent-water samples fortified at 

concentrations from 0.015 to 0.1 microgram per liter—Continued 

Rank P-Code Short name

Fortification

level 

(μg/L) 

Median

conc. 

(μg/L) 

F-pseu

(μg/L) 

Median

recovery

(percent)

Rel 

F-pseu

(percent)

MDL

(μg/L) 

Preliminary

LRL 

(μg/L) 

Remark

code

Degradates

1002 61615 2-[2-Ethyl-6-m_panol 0.1 0.087 0.01831 87.4 20.9 0.0575 0.1256 –

1007 61618 2-Chloro-2,6-d_ilide 0.015 0.013 0.00070 83.3 5.6 0.0021 0.0050 –

1008 61665 4-(Hydroxymeth_halin)

1 0.1 0.081 0.01920 80.6 23.6 0.0455 0.1428 –

1016 61674 Terbufos-O-ana_lfone 0.075 0.039 0.00587 52.1 15.0 0.0176 0.0676 –

1033 61625 3,4-Dichloroaniline 0.015 0.010 0.00049 64.6 5.0 0.0015 0.0045 –

1043 61629 3-Phenoxybenzy_cohol 0.075 0.042 0.00436 56.1 10.3 0.0131 0.0466 –

1044 79842 c-Methyl-3-(2,_ylate 0.015 0.004 0.00165 25.2 10.5 0.0049 0.0393 –

1044 79843 t-Methyl-3-(2,_ylate 0.015 0.007 0.00250 44.7 19.9 0.0075 0.0335 –

1049 61663 Paraoxon-ethyl 0.025 0.016 0.00063 62.6 5.7 0.0019 0.008 – 

1060 61652 Malaoxon 0.025 0.013 0.00042 50.4 6.6 0.0013 0.008 – 

1062 61637 2-(4-tert-buty_xanol 0.015 0.011 0.00133 74.0 15.3 0.0040 0.0108 –

1067 61640 Disulfoton sulfone 0.015 0.006 0.00113 42.5 7.3 0.0034 0.0159 –

1071 61642 Endosulfan ether 0.015 0.015 0.00068 103.0 7.5 0.0020 0.0041 –

1071 61590 Endosulfan sulfate 0.015 0.009 0.00056 57.8 4.8 0.0017 0.0058 –

1076 61671 Tefluthrin met_9364] 0.015 0.005 0.00083 32.0 8.2 0.0025 0.0156 –

1093 61627 3,5-Dichloroaniline 0.015 0.012 0.00061 78.0 5.9 0.0018 0.0047 –

1099 61614 2,5-Dichloroaniline 0.015 0.010 0.00293 67.3 10.9 0.0088 0.0261 –

1124 61660 O-Ethyl-O-meth_ioate 0.015 0.010 0.00094 68.3 24.9 0.0028 0.0083 –

1126 61645 Fenamiphos sulfone 0.075 0.027 0.00046 35.7 6.9 0.0014 0.0077 –

1231 61669 Tebupirimphos,_logue 0.015 0.010 0.00069 65.8 7.0 0.0021 0.0063 –

1002 61620 2-Ethyl-6-meth_iline 0.015 0.011 0.00054 72.3 5.0 0.0016 0.0045 E

1012 61636 Chlorpyrifos, _nalog 0.075 0.027 0.00332 35.4 12.5 0.0099 0.0562 E

1013 61617 2-Amino-N-isop_amide 0.015 0.007 0.00038 46.3 5.4 0.0011 0.0049 E

1014 61664 Paraoxon-methyl 0.075 0.048 0.00321 64.3 6.7 0.0096 0.0299 E

1015 61633 4-Chloro-2-met_henol 0.015 0.007 0.00044 46.7 6.3 0.0013 0.0056 E

1024 61630 3-Trifluoromet_iline 0.015 0.005 0.00055 30.5 12.0 0.0016 0.0108 E

1032 49295 1-Naphthol 0.025 0.021 0.01212 82.4 58.8 0.0363 0.0882 E

1032 61611 1,4-Naphthaquinone 0.025 0.008 0.00277 32.6 23.3 0.0083 0.0509 E

1034 61666 Phorate oxon 0.075 0.012 0.00258 15.9 10.3 0.0077 0.0973 E

1053 61635 Azinphos-methyl-oxon 0.015 0.025 0.00027 33.5 3.3 0.0008 0.016 E 

1054 61649 Fonofos, oxyge_nalog 0.015 0.008 0.00020 55.9 3.2 0.0006 0.0021 E

1067 61641 Disulfoton sulfoxide 0.075 0.081 0.00040 107.5 8.3 0.0012 0.0024 E

1076 61672 Tefluthrin met_2912] 0.015 0.009 0.00104 60.3 8.1 0.0031 0.0103 E

1101 61631 4,4'-Dichlorob_enone 0.015 0.013 0.00048 85.3 6.1 0.0014 0.0034 E

1105 61634 4-Chlorobenzyl_lfone 0.015 0.008 0.00265 52.2 8.5 0.0083 0.0304 E

1125 61668 Phosmet oxon 0.1 0.031 0.00287 31.1 8.6 0.0086 0.0553 E

46 Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry
Table 10. Method detection limits and preliminary laboratory reporting levels for pesticides and pesticide 

degradates calculated from determination of the analytes in eight reagent-water samples fortified at 

concentrations from 0.015 to 0.1 microgram per liter—Continued 

Rank P-Code Short name

Fortification

level 

(μg/L) 

Median

conc. 

(μg/L) 

F-pseu

(μg/L) 

Median

recovery

(percent)

Rel 

F-pseu

(percent)

MDL

(μg/L) 

Preliminary

LRL 

(μg/L) 

Remark

code

1126 61646 Fenamiphos sulfoxide 0.075 0.033 0.00014 44.5 2.2 0.0004 0.031 E 

1134 61644 Ethion monoxon 0.015 0.006 0.00241 43.0 29.6 0.0072 0.0336 E

1153 38775 Dichlorvos 0.025 0.011 0.00089 45.2 7.9 0.0027 0.0118 E

1227 61647 Fenthion sulfoxide 0.015 0.008 0.00068 51.6 8.8 0.0021 0.0079 E

Surrogates

99223 Diazinon-d10, _ogate 0.015 0.081 0.00187 81.0 2.3 0.0056 0.0138 – 

99224 alpha-HCH-d6, _ogate 0.015 0.091 0.00065 91.3 0.7 0.0019 0.0043 – 

1

MDL for temephos and 4-(hydroxymethyl)pendamethalin were estimated from reagent-water set-spike data (table 17) 

with t = 2.39.

F-pseudosigma has been used rather than the 

standard deviation. The F-pseudosigma is 

defined as the interquartile range divided by

1.349 (Hoaglin, 1983). Because the 

nonparametric summaries are less likely to be 

influenced by an outlying result, they are

more robust than their parametric equivalents 

in the small data sets produced in the method 

validation experiments. 

Recovery at different concentrations: 

The median recovery of most compounds was 

comparable at 1.0, 0.1, or 0.01 μg/L (tables 6 

through 10), which indicated no major bias 

caused by the concentration of the analyte 

over the concentration range tested. For all 

sample matrices, samples were grouped by

concentration and compared by using the 

nonparametric Mann-Whitney test to examine 

the null hypothesis that the median recoveries 

were equal to the median recovery at 0.1 μg/L

in each concentration (Miller and Miller, 

1993). For other compounds, the median 

recoveries were significantly higher (p <0.05; 

Mann-Whitney test) in the 0.1-μg/L sample 

set compared to the 1.0-μg/L set. These 

differences were small (4 to 15 percent) and 

might be the result of variation in instrument 

performance because each sample set (same 

matrix and concentration) was analyzed at

different times. The CCVs for the groundwater low-concentration set were also high, 

perhaps explaining an instrument analytical

effect rather than sample matrix or

concentration effects for some of the analytes 

determined in this set.

Recovery in different matrices: The 

mean recovery of some compounds was lower 

in the reagent-water sample sets (tables 6 and 

7) compared to samples of surface water 

(table 8) or ground water (table 9). Again, 

these differences were small (4 to 15 percent) 

and might be the result of variation in 

instrument performance because each sample

set was analyzed at different times. 

Recommended Holding Time 

The recommended holding time of

analytes in pesticide-grade water at 4oC and 

after extraction on the SPE column with 

storage on the dry column at room 

temperature was estimated by modifying a

standard practice (ASTM Procedure 

D-4841-88) for estimating holding time for 

constituents in water samples (American

Final Method Validation 47
Society for Testing and Materials, 2000). In

that standard, the maximum holding time is 

defined as the maximum period that a sample

can be stored before the analyte degrades so 

that the systematic error exceeds the 99-

percent confidence interval (not to exceed 15 

percent) of the mean concentration 

determined at time zero. Holding time is 

estimated by replicate analyses at discrete

time intervals of a large volume of sample. A 

plot of the data then is prepared, and a line is 

fit to the data. The point where the line

crosses the lower tolerable range of variation 

is the estimated holding time. An estimate of

the analyte variability is needed to calculate

the number of replicates required for each 

discrete time interval prior to determining the

holding time. 

It should be noted that the holding-time 

estimates were determined in reagent water.

In environmental samples, the sample matrix

might result in holding times different than

those determined in a relatively clean matrix

like reagent water. These holding times are

recommended to provide a balance between 

the practical requirements of sample

collection, shipping and processing, and the 

limited information provided by these

estimated holding-time experiments. In

general, the best approach is to extract 

samples by SPE and elute from the SPE 

column as quickly as possible. 

The practice was modified for use in

this report to better match the data produced

in the validation experiments and identify

analytes that have holding times shorter than

those described in the complementary method 

2001 (Zaugg and others, 1995). In method 

2001, the recommended maximum holding

times are 4 days in water prior to SPE, and 7 

days on the SPE column after SPE (Zaugg

and others, 1995, p. 39). The relative Fpseudosigma was used instead of the relative 

standard deviation to calculate the number of 

replicates needed at each discrete time 

interval. Similarly, instead of the standard

deviation, the F-pseudosigma was used to 

calculate the tolerable range of variation. The 

F-pseudosigma generally is similar to the 

standard deviation for most compounds, and, 

therefore, the modification is expected to have 

little effect except when variability is high

because of outliers. In that case, the Fpseudosigma provides a more conservative 

estimate than the standard deviation. A linear 

fit of the data rather than other graphical 

estimates was used to estimate maximum 

holding time to simplify the analysis. Visual

examination of the data was used to make 

sure the linear fit did not underestimate the 

holding times for water and on the SPE 

column given in Zaugg and others (1995), 

although, in some cases, other types of 

graphical fit might provide better numerical 

estimates of holding time. 

Calculation of replicates required for 

holding-time experiments: The relative 

F-pseudosigma of samples fortified in 

pesticide-grade water at 0.1 μg/L (tables 6 

and 7) was used to estimate the number of

samples needed to evaluate a significant

change in concentration over time. The

number of replicates required for the holdingtime experiments was calculated according to 

the following equation: 

n = 

2











D

t Rel Fpseu 

 , (12)

where n = number of replicate samples; 

t = Student's t-value for a two-tailed 

test appropriate for the 

99-percent confidence level; 

Rel Fpseu = Relative F-pseudosigma, 

in percent (tables 6 and 7); and 

 D = 15 percent, maximum variation 

from mean to be tolerated. 

48 Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry
The value of t is 3.499 for eight 

replicates and a 99-percent confidence level. 

For most compounds, the calculated number 

of replicates n was less than four (tables 11 

and 12), so this value was selected as a 

practical number of replicates to use for the 

holding-time study. For some of the more

variable analytes, the use of four replicates is

insufficient to characterize the estimated 

holding time. 

SPE holding-time experiment: Reagentwater samples were fortified with parent 

pesticides or degradates at 0.1 μg/L, extracted 

by SPE, and the column was dried on day

zero. The SPE columns then were stored at

room temperature. Four replicate samples 

were eluted from the SPE columns at discrete

(0, 1, 3, 7, 14, and 28 days) intervals over 28 

days. Parent pesticides and degradates were 

prepared and determined in separate

experiments to avoid bias from formation of 

degradates during the holding-time

experiment. 

Pesticide-grade water holding-time 

experiment: Reagent-water samples were

fortified with parent pesticides or degradates 

at 0.1 μg/L and stored at 4oC. Four replicate 

samples were extracted at discrete (0, 1, 3, 7, 

14, and 28 days) intervals over 28 days. 

Parent pesticides and degradates were 

prepared and determined in separate

experiments to avoid bias from formation of 

degradates during the holding-time

experiment. 

Holding-time data analysis: All 

samples from either the SPE or water holdingtime experiments were analyzed in one batch 

at the end of the experiment. The tolerable 

variation d that was calculated from the

following formula is listed in tables 13 

and 14: 

d = ±

n

t  Fpseu , (13)

where d = range of tolerable variation 

from initial recovery, in 

 percent; 

t = Student's t-value, for a twotailed test appropriate for the 

 99-percent confidence level; 

Fpseu = F-pseudosigma (tables 6 

and 7) converted to 

 percent; and 

n = 4, number of replicates. 

The value of t is 3.499 for eight 

replicates and a 99-percent confidence level. 

The estimated d value, in percent recovery, 

then was subtracted from the day-zero value 

to give the lower tolerable range of variation 

from the day-zero recovery. Straight lines 

were fit to the data, and the day-zero intercept 

was calculated from the regression line. The 

equation for the regression line is 

R  mt  b , (14) 

where R = recovery, in percent; 

m = slope of linear regression; 

t = time, in days; and 

b = time zero intercept, in percent 

 recovery. 

The intercept of the linear fit of the

concentration in relation to the time line with 

the lower tolerable range of concentration 

gives the estimated holding time. The slope

and intercept for the linear fit of the data are

provided to allow estimates of holding times 

by using other estimates of the tolerable range

of variation. 

Holding time on dry SPE column: Ten 

parent pesticides had holding times on the dry

SPE column that were 30 days or less (table 

13). Two organothiophosphate pesticides, 

sulfotepp and sulprofos, had holding times

Final Method Validation 49
Table 11. Number of replicates required to determine estimated holding time of parent pesticides in water 

and on solid-phase-extraction columns

[Number of replicates needed at each time step to estimate the mean concentration within 15 percent (n), 

(equation 12); P-Code, National Water Information System parameter code; –, not applicable; E, estimated qualifier 

remark] 

Rank P-Code Short name

Number 

of replicates (n) 

Remark 

code

Parent pesticides 

63 04036 Prometryn 1 –

69 61603 Profenofos 2 –

71 34362 alpha-Endosulfan 1 –

75 61596 Metalaxyl 1 –

106 61600 Oxyfluorfen 4 –

108 79846 cis-Propiconazole 1 –

110 79847 trans-Propiconazole 2 –

121 61599 Myclobutanil 2 –

126 61591 Fenamiphos 1 –

127 04025 Hexazinone 1 –

128 04031 Cycloate 1 –

132 61598 Methidathion 1 –

134 82346 Ethion 1 –

211 79844 (E)-Dimethomorph 2 –

212 79845 (Z)-Dimethomorph 1 –

220 04022 Terbuthylazine

1 2 –

225 61592 Flumetralin 3 –

227 38801 Fenthion 2 –

228 61594 Isofenphos 2 –

229 61604 Propetamphos 1 –

231 61602 Tebupirimphos 2 –

28 82662 Dimethoate 30 E

30 61610 Tribuphos 8 E

71 34357 beta-Endosulfan 1 E

76 61606 Tefluthrin 10 E

83 38454 Dicrotophos 31 E

93 61593 Iprodione 2 E

102 61595 Cyhalothrin 9 E

114 61586 Cypermethrin 26 E

115 38716 Sulprofos 4 E

125 61601 Phosmet 3 E

129 61585 Cyfluthrin 22 E

131 61580 Bifenthrin 17 E

230 61605 Sulfotepp 1 E

232 61607 Temephos1 7 E

Surrogates

99223 Diazinon-d10, _ogate 1 –

99224 alpha-HCH-d6, _ogate 1 –

1

Terbuthylazine and temephos are not included in holding-time experiments.

50 Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry
Final Method Validation 51

Table 12. Number of replicates required to determine estimated holding time of degradates in water and 

on solid-phase-extraction columns 

[Number of replicates needed at each time step to estimate the mean concentration within 15 percent (n), (equation 12); 

P-Code, National Water Information System parameter code; –, not applicable; E, estimated qualifier remark] 

Rank P-Code Short name Number 

of replicates (n) 

Remark 

code 

Degradates 

1002 61615 2-[2-Ethyl-6-m_panol 3 – 

1007 61618 2-Chloro-2,6-d_ilide 1 – 

1008 61665 4-(Hydroxymeth_halin 5 – 

1014 61664 Paraoxon-methyl 1 – 

1033 61625 3,4-Dichloroaniline 6 – 

1043 61629 3-Phenoxybenzy_cohol 1 – 

1044 79842 c-Methyl-3-(2,_ylate 1 – 

1044 79843 t-Methyl-3-(2,_ylate 2 – 

1049 61663 Paraoxon-ethyl1 1 – 

1060 61652 Malaoxon 2 – 

1062 61637 2-(4-tert-buty_xanol 3 – 

1067 61640 Disulfoton sulfone 1 – 

1071 61642 Endosulfan ether 1 – 

1071 61590 Endosulfan sulfate1 1 – 

1076 61672 Tefluthrin met_2912] 1 – 

1076 61671 Tefluthrin met_9364] 4 – 

1093 61627 3,5-Dichloroaniline 3 – 

1099 61614 2,5-Dichloroaniline 2 – 

1124 61660 O-Ethyl-O-meth_ioate 2 – 

1126 61645 Fenamiphos sulfone 4 – 

1231 61669 Tebupirimphos,_logue 1 – 

1002 61620 2-Ethyl-6-meth_iline 1 E 

1012 61636 Chlorpyrifos, _nalog 45 E 

1013 61617 2-Amino-N-isop_amide 13 E 

1015 61633 4-Chloro-2-met_henol 11 E 

1016 61674 Terbufos-O-ana_lfone 5 E 

1024 61630 3-Trifluoromet_iline 4 E 

1032 49295 1-Naphthol 89 E 

1032 61611 1,4-Naphthaquinone 53 E 

1034 61666 Phorate oxon 4 E 

1053 61635 Azinphos-methyl-oxon 22 E 

1054 61649 Fonofos, oxyge_nalog 1 E 

1067 61641 Disulfoton sulfoxide 2 E 

1101 61631 4,4'-Dichlorob_enone 1 E 

1105 61634 4-Chlorobenzyl_lfone 7 E 

1125 61668 Phosmet oxon 66 E 

1126 61646 Fenamiphos sulfoxide 8 E 

1134 61644 Ethion monoxon 2 E 

1153 38775 Dichlorvos1 2 E 

1227 61647 Fenthion sulfoxide 2 E 

Surrogates 

99223 Diazinon-d10, _ogate 2 – 

99224 alpha-HCH-d6, _ogate 2 – 

1

Dichlorvos, endosulfan sulfate, and paraoxon-ethyl were analyzed in parent fortification mixture.
Table 13. Statistical data used to determine estimated holding time of parent pesticides on dry solid-phase-extraction 

columns maintained at 25 degrees Celsius

[Holding times less than 7 days shown in boldface. Reagent-water samples were fortified at 0.1 microgram per liter, isolated on 

the SPE column on day 0, and four replicate samples were eluted from the SPE column on days 0, 1, 3, 7, 14, and 28. P-Code, 

National Water Information System parameter code; d, tolerable range of variation in initial concentration (in percent recovery); 

Mean–d, mean recovery on day 0 minus d; Intercept, intercept of linear fit to holding-time results; Slope, slope of linear fit to

holding-time results; Holding time, estimated holding time (days) from least-squares regression (using a straight-line model); --,

estimated holding time greater than 28 days because compound did not decrease in concentration over 28-day test period; –, not

applicable; E, estimated qualifier remark] 

Rank P-Code Short name

d

(percent)

Mean

recovery

day 0

(percent)

Mean–d 

(percent)

Intercept

(percent) Slope

Holding 

time

(days)

Remark 

code

Parent pesticides 

63 04036 Prometryn 6.0 84.8 78.7 83.3 0.014 -- –

69 61603 Profenofos 6.1 70.9 64.8 69.7 -0.955 7 –

71 34362 alpha-Endosulfan 4.5 97.8 93.3 102.0 0.026 -- –

75 61596 Metalaxyl 5.8 88.3 82.5 88.5 -0.043 -- –

106 61600 Oxyfluorfen 7.3 63.9 56.5 63.5 -0.170 -- –

108 79846 cis-Propiconazole 3.4 70.0 66.6 70.9 0.025 -- –

110 79847 trans-Propiconazole 5.9 82.5 76.6 82.8 0.007 -- –

121 61599 Myclobutanil 5.8 78.5 72.6 79.5 -0.001 -- –

126 61591 Fenamiphos 4.0 54.6 50.6 66.5 -0.085 -- –

127 04025 Hexazinone 2.4 56.5 54.1 60.8 -0.086 28 –

128 04031 Cycloate 5.1 77.8 72.6 76.2 0.114 -- –

132 61598 Methidathion 3.1 75.9 72.7 76.5 0.021 -- –

134 82346 Ethion 2.7 66.6 64.0 65.8 -0.048 -- –

211 79844 (E)-Dimethomorph 7.7 68.5 60.9 68.9 -0.038 -- –

212 79845 (Z)-Dimethomorph 5.5 63.9 58.4 65.2 -0.075 -- –

220 04022 Terbuthylazine

1 7.7 – – – – – –

225 61592 Flumetralin 6.3 68.6 62.3 69.9 -0.254 25 –

227 38801 Fenthion 6.2 85.5 78.8 82.3 -1.363 2 7 –

228 61594 Isofenphos 4.3 85.0 78.3 82.1 -0.038 -- –

229 61604 Propetamphos 5.8 82.6 83.8 81.6 -0.022 -- –

231 61602 Tebupirimphos 21.0 89.6 0.0 87.1 -0.019 -- –

28 82662 Dimethoate 6.7 16.7 46.4 16.7 -0.004 2 -- E

30 61610 Tribuphos 3.9 53.1 38.4 50.8 -0.287 2 24 E

71 34357 beta-Endosulfan 5.7 107.2 101.4 109.8 -0.193 30 E

76 61606 Tefluthrin 6.1 42.3 4.5 40.3 -0.018 -- E

83 38454 Dicrotophos 4.3 10.6 87.2 14.9 0.086 -- E

93 61593 Iprodione 2.0 91.4 29.2 88.2 0.072 2 -- E

102 61595 Cyhalothrin 11.6 31.2 36.4 30.2 -0.090 2 22 E

114 61586 Cypermethrin 7.4 48.0 31.9 49.9 -0.075 2 -- E

115 38716 Sulprofos 7.8 71.6 63.8 68.8 -1.415 6 E 

125 61601 Phosmet 10.7 39.3 36.5 37.3 -0.281 2 27 E

129 61585 Cyfluthrin 4.0 47.1 29.0 50.9 -0.029 -- E

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

52
Table 13. Statistical data used to determine estimated holding time of parent pesticides on dry solid-phase-extraction 

columns maintained at 25 degrees Celsius—Continued 

Rank P-Code Short name

d

(percent)

Mean

recovery

day 0

(percent)

Mean–d 

(percent)

Intercept

(percent) Slope

Holding 

time

(days)

Remark 

code

131 61580 Bifenthrin 9.0 32.9 76.5 32.2 0.053 2 -- E

230 61605 Sulfotepp 4.1 83.2 79.1 80.2 -1.218 4 E 

232 61607 Temephos1 7.0 – – – – – E

Surrogates

99223 Diazinon-d10, _ogate 3.7 97.9 94.2 94.6 -0.316 12 – 

99224 alpha-HCH-d6, _ogate 5.7 91.0 85.3 88.9 -0.126 -- – 

1

Terbuthylazine and temephos were not included in holding-time experiments. 2

Holding times (days) were corrected in pdf version of the report, February 4, 2002 (mws). 

Table 14. Statistical data used to determine estimated holding time of degradates on solid-phase-extraction columns 

maintained at 25 degrees Celsius

[Holding times less than 7 days shown in boldface. Reagent-water samples were fortified at 0.1 microgram per liter, isolated on 

the SPE column on day 0, and four replicate samples were eluted from the SPE column on days 0, 1, 3, 7, 14, and 28. P-Code, 

National Water Information System parameter code; d, tolerable range of variation in initial concentration (in percent recovery); 

Mean–d, mean recovery on day 0 minus d; Intercept, intercept of linear fit to holding-time results; Slope, slope of linear fit to

holding-time results; Holding time, estimated holding time (days) from least-squares regression (using a straight-line model); –,

not applicable; --, estimated holding time greater than 28 days because compound did not decrease in concentration over 28-day

test period; E, estimated qualifier remark]

Rank P-Code Short name

d

(percent)

Mean

recovery

day 0

(percent)

Mean–d 

(percent)

Intercept 

(percent) Slope

Holding 

time

(days)

Remark

code

Degradates

1002 61615 2-[2-Ethyl-6-m_panol 9.3 91.8 82.5 90.1 -0.836 12 –

1007 61618 2-Chloro-2,6-d_ilide 3.2 92.9 89.8 94.6 -0.153 21 –

1008 61665 4-(Hydroxymeth_halin 13.5 91.0 77.5 92.1 0.105 -- –

1016 61674 Terbufos-O-ana_lfone 14.7 93.9 91.2 87.4 -1.060 12 –

1043 61629 3-Phenoxybenzy_cohol 4.2 70.0 65.8 74.7 -0.334 13 –

1044 79842 c-Methyl-3-(2,_ylate 4.9 95.4 90.5 93.2 -0.101 -- –

1044 79843 t-Methyl-3-(2,_ylate 7.0 94.4 87.4 94.6 -0.109 -- –

1049 61663 Paraoxon-ethyl

1 5.0 70.5 65.5 67.8 -0.596 9 –

1060 61652 Malaoxon 9.1 92.6 83.5 88.5 -0.855 11 –

1062 61637 2-(4-tert-buty_xanol 9.9 83.6 73.7 88.0 -0.157 -- –

1067 61640 Disulfoton sulfone 5.8 86.0 80.2 86.3 -0.049 -- –

1071 61642 Endosulfan ether 4.7 105.8 101.1 108.9 -0.233 21 –

1071 61590 Endosulfan sulfate

1 5.7 102.5 96.8 103.4 -0.032 – –

1076 61672 Tefluthrin met_2912] 4.2 69.0 64.8 69.2 -0.291 15 –

1093 61627 3,5-Dichloroaniline 11.2 107.5 96.3 109.6 -0.794 15 –

1099 61614 2,5-Dichloroaniline 8.8 89.5 80.7 92.4 -0.268 -- –

1124 61660 O-Ethyl-O-meth_ioate 8.3 87.8 79.5 89.3 -0.042 -- –

Final Method Validation 53
Table 14. Statistical data used to determine estimated holding time of degradates on solid-phase-extraction columns 

maintained at 25 degrees Celsius—Continued 

Rank P-Code Short name

d

(percent)

Mean

recovery

day 0

(percent)

Mean–d 

(percent)

Intercept 

(percent) Slope

Holding 

time

(days)

Remark

code

1126 61645 Fenamiphos sulfone 9.3 65.2 55.9 67.3 -0.152 -- –

1231 61669 4.4 78.7 80.5 -0.375 –

61620 2-Ethyl-6-meth_iline 87.0 83.6 -0.783 5 

Tebupirimphos,_logue 74.3 12

1002 3.4 95.5 E 

1012 61636 Chlorpyrifos, _nalog 8.8 71.0 62.2 60.7 -17.963 1 E 

1013 61617 2-Amino-N-isop_amide 15.4 93.4 78.0 95.2 -0.159 -- E

1014 61664 Paraoxon-methyl 12.4 57.4 81.6 52.4 -0.879 12 E

1015 61633 4-Chloro-2-met_henol 3.9 78.0 79.9 0.048 5 

1024 3-Trifluoromet_iline 17.2 60.8 61.4 -- E

1032 49295 5.3 229.3 145.7 -5.886 E

61611 1,4-Naphthaquinone 18.2 22.2 20.1 -1.186 E

61625 3,4-Dichloroaniline 10.3 76.7 108.3 -1.321 E 

61666 Phorate oxon 86.9 211.3 -2.107 4 

1053 Azinphos-methyl-oxon 20.0 53.5 48.8 -0.479 --

53.6 E 

61630 56.5 -0.852

1-Naphthol 51.2 7

1032 40.4 16

1033 105.9 5 

1034 18.0 77.2 E 

61635 33.5 E

1054 61649 Fonofos, oxyge_nalog 3.4 82.7 79.3 77.8 -1.412 3 E 

1067 61641 Disulfoton sulfoxide 12.2 153.5 141.3 0.343 -- E

1076 61671 6.0 69.8 69.2 -0.583 E

61631 4,4'-Dichlorob_enone 4.6 75.5 81.0 5 E 

172.4

Tefluthrin met_9364] 63.8 11

1101 80.1 -0.957

1105 61634 4-Chlorobenzyl_lfone 12.8 58.2 45.4 62.9 -0.055 -- E

1125 61668 Phosmet oxon 17.9 31.0 13.1 19.9 -0.194 -- E

1126 61646 Fenamiphos sulfoxide 5.0 15.3 10.3 19.6 -0.008 -- E

1134 61644 Ethion monoxon 3.8 67.7 63.9 66.9 -0.198 20 E

1153 38775 Dichlorvos1 7.1 59.8 52.6 38.9 -1.672 5 E 

1227 61647 Fenthion sulfoxide 6.2 69.6 63.4 70.5 -0.057 -- E

Surrogates

99223 Diazinon-d10, _ogate 9.0 101.3 92.3 102.9 -0.321 28 – 

99224 alpha-HCH-d6, _ogate 5.0 100.9 96.0 100.1 0.002 -- – 

1

Dichlorvos, endosulfan sulfate, and paraoxon-ethyl were analyzed in parent fortification mixture. 

less than 7 days. Because this is shorter than 

the holding time recommended in method 

2001 (Zaugg and others, 1995), these 

compounds are reported with an estimated 

remark qualifier. Another organothiophosphate pesticide, profenofos, had a slightly

longer holding time of 7 days. 

More pesticide degradates (table 14) had 

holding times less than 30 days when

compared to the parent pesticides (table 13). 

Eight degradates had estimated holding times 

less than 7 days. This is shorter than the 

holding time recommended in method 2001 

(Zaugg and others, 1995), so these 

compounds are reported with an estimated 

remark qualifier. Two organophosphate 

degradates, chlorpyrifos oxygen analog and 

fonophos oxygen analog, appeared to be 

unstable with holding times of 3 days or less. 

This might eliminate any advantages to onsite SPE for these compounds. 

Holding time in pesticide-grade water: 

Twelve parent pesticides had calculated

54 Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry
holding times in pesticide-grade water of less 

than 30 days (table 15). An organothiophosphate pesticide (phosmet), an isomer of 

an organochlorine pesticide (betaendosulfan), and a pyrethroid pesticide 

(cyhalothrin) had holding times of 4 days or

less, which is the recommended holding time

in water for method 2001. As a result, these 

analytes are reported with an estimated 

remark qualifier.

In addition to cyhalothrin, other 

pyrethroid pesticides, cyfluthrin, 

cypermethrin, and tefluthrin had calculated 

holding times of less than 30 days. This 

might be caused by sorption to the walls of 

the glass sample bottles over the duration of

the experiments because these compounds 

have high octanol-water partition coefficients 

(log Kow) compared to the other analytes 

(Mackay and others, 1997). None of the 

degradates had holding times in water less 

than 4 days (table 16). 

 Fortified Reagent-Water-Set

Samples 

Environmental water samples collected

by some NAWQA projects were analyzed in 

1999 as part of a pilot test during

implementation of the new method. Reagentwater samples were fortified with the analytes

at 0.1 μg/L and analyzed with each set of 10 

samples. The median recovery and variability

of 74 of these fortified reagent-water-set 

samples prepared during March–December, 

1999, are listed in table 17. Degradates were 

included in all 74 samples, while parent 

pesticides were included only in the last 49 

samples. These fortified reagent-water-set

samples are comparable to the lowconcentration, reagent-water samples 

analyzed during method validation (tables 6 

and 7). They probably better represent the 

performance of the analytes in pesticide-grade 

water because they were analyzed in many

different sets and over a longer period 

compared to the reagent-water data listed in 

tables 6 and 7. For most analytes, median 

recovery in the fortified reagent-water-set

samples was comparable to that in the

reagent-water method validation data listed in 

tables 6 and 7, although the variability is 

somewhat larger. 

NOTE: During the pilot test of the method, 

environmental samples were extracted by

SPE, generally within 4 days of collection, 

processed, and the extracts stored in a freezer 

until GC/MS analysis. Repeated GC/MS 

analysis of a CCV standard stored for a 20-

week period indicated no significant loss of 

any analytes. 

The average median recovery for the 

fortified reagent-water-set samples for all 

compounds was 68 percent, with an average Fpseudosigma of 12 percent. 

Some analytes, however, exhibited 

significantly larger variability in the fortified 

reagent-water-set samples, perhaps indicating

analytes that are more susceptible to

procedural error than others. A plot of the 

median concentration and F-pseudosigma for 

all analytes is shown in figure 2. A line of 

relative F-pseudosigma equal to 25 percent is 

plotted to indicate analytes that have high Fpseudosigma compared to other analytes. 

Compounds that had an F-pseudosigma 

greater than 25 percent include the following: 

1,4-naphthaquinone; 1-naphthol, 3-

trifluoromethylaniline; 4-chloro-2-

methylphenol; azinphos-methyl-oxon; 

chlorpyrifos oxygen analog, cyhalothrin; 

cypermethrin; dichlorvos; ethion monoxon; 

fenamiphos sulfoxide; fenthion sulfoxide; 

iprodione; phosmet; phosmet oxon; and 

temephos. 

Qualification of Some Compounds 

During quantitative method validation, 

some compounds exhibited performance

Final Method Validation 55
Table 15. Statistical data used to determine estimated holding time of parent pesticides in pesticide-grade water 

maintained at 4 degrees Celsius

[Analytes with holding times less than 4 days shown in bold. Reagent-water samples were fortified at 0.1 microgram per 

liter, and four replicate samples were extracted and prepared for analysis on days 0, 1, 3, 7, 14, and 28. P-Code, National 

Water Information System parameter code; d, tolerable range of variation from mean recovery, in percent; Mean –d, mean

recovery on day 0 minus d; Intercept, intercept of linear fit to holding-time results; Slope, slope of linear fit to holding-time

results; --, estimated holding time greater than 28 days because compound did not decrease in concentration over 28-day test

period; –, not applicable; E, estimated qualifier remark] 

Rank P-Code Short name

d

(percent)

Mean

recovery

day 0

(percent)

Mean–d

(percent)

Intercept 

(percent) Slope

Holding 

time

(days)

Remark

code

Parent pesticides 

63 04036 Prometryn 6.0 84.7 78.7 84.9 0.142 -- –

69 61603 Profenofos 6.1 72.2 66.0 66.8 -0.832 8 –

71 34362 alpha-Endosulfan 4.5 92.2 87.7 80.7 -0.851 6 –

75 61596 Metalaxyl 5.8 87.9 82.1 90.5 0.204 -- –

106 61600 Oxyfluorfen 7.3 61.8 54.5 58.6 -0.124 -- –

108 79846 cis-Propiconazole 3.4 69.7 66.2 68.0 -0.017 -- –

110 79847 trans-Propiconazole 5.9 79.7 73.8 77.2 0.023 -- –

121 61599 Myclobutanil 5.8 76.4 70.6 76.2 0.086 -- –

126 61591 Fenamiphos 4.0 70.9 66.9 70.2 0.141 -- –

127 04025 Hexazinone 2.4 62.4 60.0 60.7 -0.272 9 –

128 04031 Cycloate 5.1 81.0 75.8 84.4 -0.224 24 –

132 61598 Methidathion 3.1 71.1 68.0 69.3 -0.045 -- –

134 82346 Ethion 2.7 64.6 61.9 62.4 -0.042 -- –

211 79844 (E)-Dimethomorph 7.7 71.4 63.8 73.9 0.008 -- –

212 79845 (Z)-Dimethomorph 5.5 69.0 63.5 68.5 0.040 -- –

220 04022 Terbuthylazine

1 7.7 – – – – – –

225 61592 Flumetralin 6.3 66.2 59.9 64.7 -0.042 -- –

227 38801 Fenthion 9.0 77.9 68.9 79.9 0.080 -- –

228 61594 Isofenphos 6.2 85.3 79.1 83.7 0.035 -- –

229 61604 Propetamphos 4.3 81.8 77.5 81.4 0.089 -- –

231 61602 Tebupirimphos 5.8 84.3 78.5 86.4 0.090 -- –

28 82662 Dimethoate 21.0 17.6 0.0 27.1 0.570 -- E

30 61610 Tribuphos 6.7 53.9 47.2 50.1 -0.070 -- E

71 34357 beta-Endosulfan 5.7 98.5 92.7 78.8 -1.714 4 E 

76 61606 Tefluthrin 3.9 43.4 39.5 47.4 -0.148 27 E

83 38454 Dicrotophos 6.1 18.2 12.1 22.2 -0.142 -- E

93 61593 Iprodione 4.3 80.0 75.7 74.6 -0.661 7 E

102 61595 Cyhalothrin 2.0 29.8 27.8 23.5 -0.700 3 E 

114 61586 Cypermethrin 11.6 52.6 41.0 53.0 -0.784 15 E

115 38716 Sulprofos 7.8 61.3 53.5 62.3 -0.061 -- E

125 61601 Phosmet 7.4 27.0 19.6 27.0 -4.525 2 E 

129 61585 Cyfluthrin 10.7 51.6 40.9 52.2 -0.750 15 E

131 61580 Bifenthrin 4.0 37.2 33.3 37.8 -0.084 -- E

230 61605 Sulfotepp 4.1 79.2 75.1 79.8 -0.496 9 E

232 61607 Temephos1 7.0 – – – – – E

Surrogates

99223 Diazinon-d10, _ogate 3.7 89.8 86.2 93.1 -0.036 -- – 

99224 alpha-HCH-d6, _ogate 5.7 88.8 83.1 94.5 0.002 -- – 

1

Terbuthylazine and temephos were not included in holding-time experiments.

56 Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry
Table 16. Statistical data used to determine estimated holding time of degradates in pesticide-grade water

maintained at 4 degrees Celsius

[Analytes with holding times less than 4 days shown in bold. Reagent-water samples were fortified at 0.1 microgram per 

liter, and four replicate samples were extracted and prepared for analysis on days 0, 1, 3, 7, 14, and 28. P-Code, National 

Water Information System parameter code; d, tolerable range of variation from mean recovery, in percent; Mean –d, mean

recovery on day 0 minus d; Intercept, intercept of linear fit to holding-time results; Slope, slope of linear fit to holding-time

results; --, estimated holding time greater than 28 days because compound did not decrease in concentration over 28-day test

period; –, not applicable; E, estimated qualifier remark] 

Rank P-Code Short name

d 

(percent)

Mean

recovery

day 0

(percent)

Mean–d

(percent)

Intercept 

(percent) Slope

Holding 

time

(days)

Remark

code

Degradates

1002 61615 2-[2-Ethyl-6-m_panol 9.3 72.3 63.0 73.3 0.104 -- –

1007 61618 2-Chloro-2,6-d_ilide 3.2 86.1 82.9 86.3 0.042 -- –

1008 61665 4-(Hydroxymeth_halin 13.5 106.5 92.9 105.1 0.018 -- –

1016 61674 Terbufos-O-ana_lfone 12.4 59.6 47.2 52.4 -0.332 -- –

1033 61625 3,4-Dichloroaniline 14.7 85.3 70.7 89.9 0.258 -- –

1043 61629 3-Phenoxybenzy_cohol 4.2 74.0 69.8 76.2 -0.022 -- –

1044 79842 c-Methyl-3-(2,_ylate 4.9 90.2 85.3 89.5 -0.083 -- –

1044 79843 t-Methyl-3-(2,_ylate 7.0 90.8 83.7 90.0 -0.030 -- –

1049 61663 Paraoxon-ethyl

1 5.0 65.9 61.0 66.4 0.085 -- –

1060 61652 Malaoxon 9.1 67.4 58.3 54.0 -0.409 23 –

1062 61637 2-(4-tert-buty_xanol 9.9 80.7 70.9 81.2 -0.002 -- –

1067 61640 Disulfoton sulfone 5.8 53.5 47.7 50.9 -0.194 30 –

1071 61642 Endosulfan ether 4.7 103.9 99.2 100.6 0.016 -- –

1071 61590 Endosulfan sulfate

1 5.7 93.2 87.5 92.3 0.034 -- –

1076 61672 Tefluthrin met_2912] 4.2 70.1 65.9 70.3 -0.074 -- –

1093 61627 3,5-Dichloroaniline 11.2 88.7 77.5 92.1 0.230 -- –

1099 61614 2,5-Dichloroaniline 8.8 81.2 72.4 83.1 0.120 -- –

1124 61660 O-Ethyl-O-meth_ioate 8.3 80.9 72.6 82.0 0.156 -- –

1126 61645 Fenamiphos sulfone 9.3 72.0 62.7 68.2 -0.140 -- –

1231 61669 Tebupirimphos,_logue 4.4 75.9 71.5 76.1 -0.058 -- –

1002 61620 2-Ethyl-6-meth_iline 3.4 89.7 86.3 93.0 0.166 -- E

1012 61636 Chlorpyrifos, _nalog 8.8 56.7 47.8 55.6 0.266 -- E

1013 61617 2-Amino-N-isop_amide 15.4 50.8 35.3 54.6 0.289 -- E

1014 61664 Paraoxon-methyl 3.9 79.7 75.8 76.0 0.359 -- E

1015 61633 4-Chloro-2-met_henol 17.2 58.0 40.8 65.3 0.393 -- E

1024 61630 3-Trifluoromet_iline 5.3 52.0 46.7 53.4 0.108 -- E

1032 49295 1-Naphthol 18.0 97.8 79.8 113.5 0.706 -- E

1032 61611 1,4-Naphthaquinone 18.2 42.2 24.1 39.4 0.002 -- E

1034 61666 Phorate oxon 10.3 72.2 62.0 70.8 -1.371 8 E

1053 61635 Azinphos-methyl-oxon 20.0 35.1 15.0 37.2 0.389 -- E

1054 61649 Fonofos, oxyge_nalog 3.4 65.0 61.7 66.8 0.181 -- E

1067 61641 Disulfoton sulfoxide 12.2 121.4 109.3 122.7 0.409 -- E

1076 61671 Tefluthrin met_9364] 6.0 55.3 49.3 54.8 -0.250 24 E

1101 61631 4,4'-Dichlorob_enone 4.6 69.0 64.4 71.8 0.104 -- E

Final Method Validation 57
Table 16. Statistical data used to determine estimated holding time of degradates in pesticide-grade 

water maintained at 4 degrees Celsius—Continued

Rank P-Code Short name

d 

(percent)

Mean

recovery

day 0

(percent)

Mean–d

(percent)

Intercept 

(percent) Slope

Holding 

time

(days)

Remark

code

1105 61634 4-Chlorobenzyl_lfone 12.8 61.7 48.9 62.3 0.064 -- E

1125 61668 Phosmet oxon 17.9 7.4 0.0 9.7 0.003 -- E

1126 61646 Fenamiphos sulfoxide 5.0 9.9 4.9 11.2 -0.034 -- E

1134 61644 Ethion monoxon 3.8 55.0 51.2 54.4 0.021 -- E

1153 38775 Dichlorvos1 7.1 35.3 28.2 33.1 0.055 -- E

1227 61647 Fenthion sulfoxide 6.2 63.8 57.7 64.7 0.057 -- E

Surrogates

99223 Diazinon-d10, _ogate 9.0 100.8 91.8 98.4 -0.068 -- –

99224 alpha-HCH-d6, _ogate 5.0 85.9 80.9 86.5 -0.104 -- –

1

Dichlorvos, endosulfan sulfate, and paraoxon-ethyl were analyzed in parent fortification mixture. 

Table 17. Bias and variability data from reagent-water-set samples fortified with analytes at low (0.1 

microgram per liter) concentrations and analyzed during March through December, 1999 

[Analytes with median recoveries less than 60 percent or greater than 120 percent, or having a relative Fpseudosigma greater than 25 percent are reported with an estimated (E) remark code. Additional analytes with short 

holding times are also reported with an estimated remark code. Rank, national application and use rank of pesticide; 

P-Code, National Water Information System parameter code; conc., concentration; μg/L, microgram per liter; F-pseu, 

F-pseudosigma (interquartile range/1.349); Rel F-pseu, relative F-pseudosigma; –, not applicable; E, estimated 

remark code] 

Rank P-Code Short name

Median

conc. 

(μg/L) 

F-pseu

(μg/L) 

Median

recovery

(percent)

Rel 

F-pseu

(percent)

Count Remark 

code

Parent pesticides 

63 04036 Prometryn 0.089 0.009 89.3 10.5 49 –

69 61603 Profenofos 0.073 0.011 72.9 14.9 49 –

71 34362 alpha-Endosulfan 0.081 0.008 81.3 9.8 49 –

75 61596 Metalaxyl 0.095 0.010 95.1 10.7 49 –

106 61600 Oxyfluorfen 0.061 0.007 61.4 11.0 49 –

108 79846 cis-Propiconazole 0.083 0.010 82.6 12.1 49 –

110 79847 trans-Propiconazole 0.081 0.009 81.4 11.6 49 –

121 61599 Myclobutanil 0.080 0.007 80.3 9.2 49 –

126 61591 Fenamiphos 0.070 0.006 70.5 9.2 49 –

127 04025 Hexazinone 0.060 0.007 60.3 12.0 49 –

128 04031 Cycloate 0.089 0.006 89.3 6.3 49 –

132 61598 Methidathion 0.077 0.010 76.9 13.1 49 –

134 82346 Ethion 0.064 0.011 64.2 16.5 49 –

211 79844 (E)-Dimethomorph 0.076 0.011 75.8 15.0 49 –

212 79845 (Z)-Dimethomorph 0.073 0.010 72.8 14.0 49 –

220 04022 Terbuthylazine 0.097 0.008 96.7 8.0 18 –

225 61592 Flumetralin 0.066 0.010 66.4 15.7 49 –

227 38801 Fenthion 0.087 0.011 86.8 12.4 49 –

58 Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry
Table 17. Bias and variability data from reagent-water-set samples fortified with analytes at low 

(0.1 microgram per liter) concentrations and analyzed during March through December, 1999—Continued 

Rank P-Code Short name

Median

conc. 

(μg/L) 

F-pseu

(μg/L) 

Median

recovery

(percent)

Rel 

F-pseu

(percent)

Count Remark 

code

228 61594 Isofenphos 0.086 0.008 85.6 9.7 49 –

229 61604 Propetamphos 0.087 0.010 86.7 11.5 49 –

231 61602 Tebupirimphos 0.086 0.008 86.4 8.7 49 –

28 82662 Dimethoate 0.035 0.007 35.3 21.2 49 E

30 61610 Tribuphos 0.044 0.008 43.7 17.4 49 E

71 34357 beta-Endosulfan 0.091 0.009 91.0 9.5 49 E

76 61606 Tefluthrin 0.032 0.006 32.4 17.7 49 E

83 38454 Dicrotophos 0.028 0.006 28.1 22.0 49 E

93 61593 Iprodione 0.074 0.034 74.3 46.1 49 E

102 61595 Cyhalothrin 0.021 0.006 20.9 30.0 49 E

114 61586 Cypermethrin 0.047 0.014 46.6 30.9 49 E

115 38716 Sulprofos 0.066 0.013 66.3 19.9 49 E

125 61601 Phosmet 0.020 0.021 20.1 104.1 49 E

129 61585 Cyfluthrin 0.044 0.010 44.3 23.3 49 E

131 61580 Bifenthrin 0.027 0.005 27.3 19.5 49 E

230 61605 Sulfotepp 0.086 0.007 86.1 8.0 49 E

232 61607 Temephos 0.034 0.015 33.9 44.5 49 E

Degradates

1002 61615 2-[2-Ethyl-6-m_panol 0.084 0.009 84.3 10.7 74 –

1007 61618 2-Chloro-2,6-d_ilide 0.087 0.011 86.6 12.1 74 –

1008 61665 4-(Hydroxymeth_halin 0.081 0.019 80.6 23.6 74 –

1016 61674 Terbufos-O-ana_lfone 0.073 0.012 72.6 16.8 49 –

1033 61625 3,4-Dichloroaniline 0.081 0.014 80.6 17.6 74 –

1043 61629 3-Phenoxybenzy_cohol 0.074 0.010 74.3 13.6 74 –

1044 79842 c-Methyl-3-(2,_ylate 0.085 0.007 85.0 8.8 74 –

1044 79843 t-Methyl-3-(2,_ylate 0.090 0.007 90.4 7.6 74 –

1049 61663 Paraoxon-ethyl 0.085 0.011 84.9 13.4 49 –

1060 61652 Malaoxon 0.076 0.015 76.4 20.0 74 –

1062 61637 2-(4-tert-buty_xanol 0.086 0.010 86.1 11.3 74 –

1067 61640 Disulfoton sulfone 0.073 0.010 72.7 13.4 74 –

1071 61642 Endosulfan ether 0.102 0.011 101.6 11.1 74 –

1071 61590 Endosulfan sulfate 0.091 0.007 91.3 7.4 49 –

1076 61672 Tefluthrin met_2912] 0.060 0.010 60.1 16.8 74 –

1093 61627 3,5-Dichloroaniline 0.091 0.011 91.2 12.6 74 –

1099 61614 2,5-Dichloroaniline 0.078 0.014 77.8 17.5 74 –

1124 61660 O-Ethyl-O-meth_ioate 0.085 0.009 85.3 10.1 74 –

1231 61669 Tebupirimphos,_logue 0.076 0.012 76.4 15.4 74 –

1002 61620 2-Ethyl-6-meth_iline 0.096 0.011 96.1 11.1 74 E

1012 61636 Chlorpyrifos, _nalog 0.039 0.023 38.8 59.5 74 E

1013 61617 2-Amino-N-isop_amide 0.055 0.012 54.7 21.9 74 E

1014 61664 Paraoxon-methyl 0.072 0.014 72.4 19.9 74 E

1015 61633 4-Chloro-2-met_henol 0.060 0.021 60.4 34.1 74 E

Final Method Validation 59
Table 17. Bias and variability data from reagent-water-set samples fortified with analytes at low 

(0.1 microgram per liter) concentrations and analyzed during March through December, 1999—Continued 

Rank P-Code Short name

Median

conc. 

(μg/L) 

F-pseu

(μg/L) 

Median

recovery

(percent)

Rel 

F-pseu

(percent)

Count Remark 

code

1024 61630 3-Trifluoromet_iline 0.041 0.015 41.1 35.9 74 E

1032 49295 1-Naphthol 0.061 0.055 60.7 90.9 73 E

1032 61611 1,4-Naphthaquinone 0.034 0.015 34.2 44.3 74 E

1034 61666 Phorate oxon 0.078 0.012 77.5 15.3 74 E

1053 61635 Azinphos-methyl-oxon 0.044 0.020 44.5 45.6 72 E

1054 61649 Fonofos, oxyge_nalog 0.077 0.007 77.0 8.6 49 E

1067 61641 Disulfoton sulfoxide 0.125 0.021 125.0 16.8 49 E

1076 61671 Tefluthrin met_9364] 0.034 0.008 33.7 24.2 74 E

1101 61631 4,4'-Dichlorob_enone 0.076 0.010 76.5 12.7 74 E

1105 61634 4-Chlorobenzyl_lfone 0.059 0.011 59.2 17.8 49 E

1125 61668 Phosmet oxon 0.016 0.013 15.6 86.3 49 E

1126 61646 Fenamiphos sulfoxide 0.022 0.010 21.9 46.5 48 E

1134 61644 Ethion monoxon 0.059 0.015 58.7 26.3 74 E

1153 38775 Dichlorvos 0.050 0.016 49.8 31.4 49 E

1227 61647 Fenthion sulfoxide 0.064 0.026 63.9 41.0 74 E

Surrogates

99223 Diazinon-d10, _ogate 0.094 0.010 94.4 10.7 74 – 

99224 alpha-HCH-d6, _ogate 0.092 0.013 91.9 14.5 74 – 

Figure 2. Bias and variability data from reagent-water-set samples fortified with analytes at low (0.1 

microgram per liter) concentrations and prepared during March through December, 1999. Line shows ratio of 

F-pseudosigma to median of 0.25, comparable to an F-pseudosigma of 25 percent (data from table 17). 

60 Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry
problems in all matrices and all 

concentrations or had short holding times. 

These analytes arereported with an estimated 

remark code to alert the data user to the

greater uncertainty associated with the 

quantitative results. The fortified reagentwater-set sample results were used to 

characterize long-term bias and variability

problems (table 17). Criteria for qualification 

as estimated were median recovery less than

60 percent or greater than 120 percent, or 

relative F-pseudosigma greater than 25 

percent. In addition, the holding-time results 

were used to qualify analytes with short 

holding times. Criteria used were holding

times in water less than 4 days or holding

times on the dry SPE column less than 7 days. 

The analytes qualified with "estimated"

are listed in table 18. Parent pesticides 

qualified with estimated remark codes 

because of median recovery less than 60 

percent were dimethoate, tribuphos, tefluthrin, 

dichrotophos, cyfluthrin, and bifenthrin. 

Degradates qualified with estimated remark

codes because of low median recovery were 

2-amino-N-isop_amide, 4-chlorobenzyl_lfone 

and tefluthrin met_9364, but disulfoton 

sulfoxide was qualified because of high

recovery. Iprodione was qualified with 

estimated remark code because of relative Fpseudosigma greater than 25 percent. 

Cyhalothrin, cypermethrin, phosmet, and 

temephos were characterized by low recovery

and high variability. Degradate analytes with 

relative F-pseudosigma greater than 25 

percent included 4-chloro-2-met_henol; 1-

naphthol and fenthion sulfoxide. Degradates 

characterized by low recovery and high

variability included 1,4-naphthaquinone; 

chlorpyrifos, _nalog; 3-trifluoromet_iline;

azinphos-methyl-oxon; phosmet oxon; 

fenamiphos sulfoxide; ethion monoxon; and 

dichlorvos. 

Analytes with holding times in water

less than or equal to 4 days included betaendosulfan, cyhalothrin, and phosmet. None 

of the degradate compounds had estimated 

holding times less than or equal to 4 days. 

Sulprofos and sulfotepp are organothiophosphate pesticides that have short holding

times on the dry SPE column, even though 

they are apparently stable for a longer time in 

water. Oxidative degradation can cause loss 

of organothiophosphate pesticides, and it 

would be useful to analyze oxidative 

degradates of these two pesticides in the 

samples to determine if these pesticides were

lost during storage on the SPE column. 

Similarly, a number of degradates appear to 

have short holding times on the dry SPE 

column, including 2-ethyl-6-meth_iline;

paraoxon-methyl; 1-naphthol; phorate oxon; 

chlorpyrifos, _nalog; and 4,4'-

dichlorob_enone. Chlorpyrifos, _nalog

appears to degrade quickly on the SPE 

column, and this might explain high

variability for this degradate in the validation 

experiments and fortified reagent-water

samples. 

OTHER CONSIDERATIONS

 Automation 

The method is ideally suited for 

automation by using laboratory systems to 

prepare samples. The method, with minor 

modifications, has been successfully used 

with an AutoTrace SPE Workstation. An 

example of the procedure and parameter setup 

used with the AutoTrace SPE Workstation is

shown in Supplement A. 

 On-Site Extraction 

The method also can be used with an 

optional on-site extraction procedure, which 

allows samples to be collected and processed at 

remote locations. This procedure reduces 

potential problems for some analytes that exceed 

the estimated pre-extraction holding-time limit in 

water of 4 days and avoids complications and 

Other Considerations 61
Table 18. Analytes qualified as estimated concentration because of large bias and variability

results of fortified reagent-water-set samples (table 17) or short holding-time results (tables 13–

16). Criteria for estimation were median recovery less than 60 percent, or greater than 120 

percent, relative F-pseudosigma more than 25 percent, holding time in water less than 4 days, or

holding time on solid-phase-extraction column less than 7 days.

[Rank, national application and use rank of pesticide; P-Code, National Water Information System parameter 

code; Rel F-pseu, Relative F-pseudosigma; d, day; SPE, solid-phase extraction; --, not within criteria; E, 

estimated remark code] 

Rank P–Code Short name

Median

recovery

(percent)

Rel 

F-pseu

(percent)

Water

hold time

(d) 

SPE 

hold time 

(d) 

Remark

code

Parent pesticides 

28 82662 Dimethoate 35.3 -- -- -- E

30 61610 Tribuphos 43.7 -- -- -- E

71 34357 beta-Endosulfan -- -- 4 -- E

76 61606 Tefluthrin 32.4 -- -- -- E

83 38454 Dicrotophos 28.1 -- -- -- E

93 61593 Iprodione -- 46.1 -- -- E

102 61595 Cyhalothrin 20.9 30.0 3 -- E

114 61586 Cypermethrin 46.6 30.9 -- -- E

115 38716 Sulprofos -- -- -- 6 E

125 61601 Phosmet 20.1 104.1 2 -- E

129 61585 Cyfluthrin 44.3 -- -- -- E

131 61580 Bifenthrin 27.3 -- -- -- E

230 61605 Sulfotepp -- -- -- 4 E

232 61607 Temephos 33.9 44.5 -- -- E

Degradates

1002 61620 2-Ethyl-6-meth_iline -- -- -- 5 E

1012 61636 Chlorpyrifos, _nalog 38.8 59.5 -- 1 E

1013 61617 2-Amino-N-isop_amide 54.7 -- -- -- E

1014 61664 Paraoxon-methyl -- -- -- 5 E

1015 61633 4-Chloro-2-met_henol -- 34.1 -- -- E

1024 61630 3-Trifluoromet_iline 41.1 35.9 -- -- E

1032 49295 1-Naphthol -- 90.9 -- 4 E

1034 61666 Phorate oxon -- -- -- 5 E

1053 61635 Azinphos-methyl-oxon 44.5 45.6 -- -- E

1054 61649 Fonofos, oxyge_nalog -- -- -- 3 E

1067 61641 Disulfoton sulfoxide 125.0 16.8 -- -- E

1076 61671 Tefluthrin met_9364] 33.7 -- -- -- E

1101 61631 4,4'-Dichlorob_enone -- -- -- 5 E

1105 61634 4-Chlorobenzyl_lfone 59.2 -- -- -- E

1125 61668 Phosmet oxon 15.6 86.3 -- -- E

1126 61646 Fenamiphos sulfoxide 21.9 46.5 -- -- E

1134 61644 Ethion monoxon 58.7 26.3 -- -- E

1032 61611 1,4-Naphthaquinone 34.2 44.3 -- -- E

1153 38775 Dichlorvos 49.8 31.4 -- -- E

1227 61647 Fenthion sulfoxide -- 41.0 -- -- E

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

62
expense of overnight shipping of samples to 

the laboratory. A holding-time study on damp 

SPE columns applicable to on-site extraction 

has not been conducted. Instructions for onsite processing are listed in Supplement B.

CONCLUSIONS

Solid-phase extraction with determination by gas chromatography/mass spectrometry is shown to be a sensitive and reliable

method for the determination of low concentrations of a broad range of pesticides and 

degradates in water samples. This report 

presents a new method for routine analysis of 

21 parent pesticides and 20 pesticide 

degradates in filtered natural-water samples. 

Estimated method detection limits range from 

0.001 to 0.057 μg/L. Another 14 parent 

pesticides and 20 pesticide degradates 

demonstrated median recoveries less than 60 

percent or greater than 120 percent, or had 

relative F-pseudosigma more than 25 percent, 

or holding times less than 4 days in water or 7 

days on the dry solid-phase-extraction 

column, and, therefore, are reported in the 

method with an estimated remark code. This 

new method complements method 2001 by

using the same sample preparation and 

analytical steps but adds 41 new analytes. 

REFERENCES CITED 

American Society for Testing and Materials, 

2000, Standard practice for estimation 

of holding time for water samples 

containing organic and inorganic 

constituents: Annual book of ASTM 

standards, Section 11, Water: West 

Conshohocken, Penn., American 

Society for Testing and Materials, 

v. 11.01, p. 485–490. 

Barbash, J.E., and Resek, E.A., 1996, 

Pesticides in ground water: Distribution, 

trends, and governing factors; Pesticides

in the hydrologic system: Chelsea, 

Mich., Ann Arbor Press, v. 2, 588 p. 

Childress, C.J., Foreman, W.T., Connor, B.F., 

and Maloney, T.J., 1999, New reporting

procedures based on long-term method 

detection levels and some considerations 

for interpretations of water-quality data

provided by the U.S. Geological Survey

National Water Quality Laboratory:

U.S. Geological Survey Open-File 

Report 99-133, 19 p. 

Dennis, W.H., Meier, E.P., Randall, W.F., 

Rosencrance, A.B., and Rosenblatt, 

D.H., 1979, Degradation of diazinon by

sodium hypochlorite. Chemistry and 

aquatic toxicity: Environmental Science

& Technology, v. 13, no. 5, p. 594–598. 

Foreman, W.T., Connor, B.F., Beaty, D.A., 

Kellogg, E.K., Maloney, T.J., and Pritt, 

J.W., 2001, A long-term approach for 

determining method detection levels and 

establishing reporting levels, in 2001 

Pittsburgh Conference Abstract Book, 

New Orleans, La., March 4–9, 2001, 

abstract no. 1374. 

Gilliom, R.J., Barbash, J.E., Kolpin, D.W., 

and Larson, S.J., 1999, Testing water 

quality for pesticide pollution: 

Environmental Science & Technology,

v. 33, no. 7, p. 164A. 

Hoaglin, D.C., 1983, Letter values: A set of 

selected order statistics, in Hoaglin, 

D.C., Mosteller, F., and Tukey, J.W., 

eds., Understanding robust and 

exploratory data analysis: New York, 

John Wiley and Sons, p. 33–54. 

Larson, S.J., Capel, P.D., and Majewski, 

M.S., 1997, Pesticides in surface water: 

Distribution, trends, and governing

factors; Pesticides in the hydrologic 

system: Chelsea, Mich., Ann Arbor 

Press, v. 3, 373 p. 

Larson, S.J., Gilliom, R.J., and Capel, P.D., 

1998, Pesticides in streams of the United 

States—Initial results from the National 

Water-Quality Assessment Program: U.S. 

Geological Survey Water-Resources 

Investigations Report 98-4222, 99 p. 

References Cited 63
Lindley, C.E., Stewart, J.T., and Sandstrom, 

M.W., 1996, Determination of low 

concentrations of acetochlor in water by

automated solid-phase extraction and 

gas chromatography with mass-selective

detection: Journal of Association of 

Official Analytical Chemists

International, v. 79, no. 4, p. 962–966. 

Mackay, D., Shiu, W.Y., and Ma, K.C., 1997, 

Pesticide chemicals: Illustrated 

handbook of physical-chemical 

properties and environmental fate for

organic chemicals: Boca Raton, Lewis 

Publishers Inc, v. V, 812 p. 

Majewski, M.J., 1997, National and study unit 

pesticide use: U.S. Geological Survey

web site, accessed July 31, 2000, at 

http://wwwdcascr.wr.usgs.gov/pnsp/natsu/ 

Miller, J.C., and Miller, J.N., 1993, Statistics 

for analytical chemistry (3d ed.): New 

York, Ellis Horwood Limited, 233 p. 

Sandstrom, M.W., 1995, Filtration of watersediment samples for the determination 

of organic compounds: U.S. Geological 

Survey Water-Resources Investigations 

Report 95-4105, 13 p. 

U.S. Environmental Protection Agency, 1997, 

Guidelines establishing test procedures 

for the analysis of pollutants (App. B,

Part 136, Definition and procedures for 

the determination of the method 

detection limit): U.S. Code of Federal 

Regulations, Title 40, p. 265–267. 

_____2001, Pesticide tolerance reassessment 

and reregistration: USEPA web site, 

accessed May 4, 2001, at URL

http://www.epa.gov/pesticides/reregistration/

U.S. Geological Survey, 2000, Pesticides 

analyzed in NAWQA samples: Use, 

chemical analyses, and water-quality

criteria: web site accessed July 31, 2000, 

at http://ca.water.usgs.gov/pnsp/anstrat/

Werner, S.L., Burkhardt, M.R., and 

DeRusseau, S.N., 1996, Methods of 

analysis by the U.S. Geological Survey

National Water Quality Laboratory—

Determination of pesticides in water by

Carbopak-B solid-phase extraction and 

high-performance liquid 

chromatography: U.S. Geological 

Survey Open-File Report 96-216, 42 p. 

Wilde, F.D., Radtke, D.B., Gibs, Jacob, and 

Iwatsubo, R.T., eds., 1999, National 

field manual for the collection of waterquality data: U.S. Geological Survey

Techniques of Water-Resources 

Investigations, book 9, chaps. A1 

through A6. 

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., 

and Fehlberg, K.M., 1995, Methods of 

analysis by the U.S. Geological Survey

National Water Quality Laboratory—

Determination of pesticides in water by

C-18 solid-phase extraction and 

capillary-column gas chromatography/ 

mass spectrometry with selected-ion 

monitoring: U.S. Geological Survey

Open-File Report 95-181, 49 p.

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

64
Supplement A—Automated Solid-Phase Extraction Procedure 
Zymark AutoTrace Extraction Workstation 1.20

AutoTrace Extraction Procedure: 2001 CONDITIONING/EXTRACTION 9/8/94

Estimated time for samples: 57.8 minutes 

Date: 8 Sep 94 

Step 1: Process 6 samples using the following procedure: 

Step 2: Condition column with 3 mL of METHANOL into SOLVENT WASTE 

Step 3: Condition column with 6 mL of WATER into SOLVENT WASTE 

Step 4: Load 1,000 mL of sample onto column 

Step 5: Dry column with gas for 4 minutes 

Step 6: Pause and alert operator, resume when CONTINUE is pressed 

Step 7: Clean each sample path with 50 mL cleaning solution 

(isopropanol: methylene chloride: toluene; 7:2:1) into SOLVENT WASTE 

Step 8: Clean each sample path with 50 mL methanol into SOLVENT WASTE 

Step 9: Clean each sample path with 100 mL distilled water into AQUEOUS WASTE 

Step 10: Dry column with gas for 0.1 minute 

Step 11: END 

Setup Parameters 

[mL/min, milliliters per minute; mL, milliliter] 

AutoTrace Extraction Workstation 

FLOW RATES 

(mL/min)

SOLID-PHASE EXTRACTION

PARAMETERS 

Condition flow: 25 Push delay: 2 seconds 

Load flow: 25 Air factor: 0.5 

Rinse flow: 25 Autowash volume: 0.00 mL

Elute flow: 5 

Condition air push: 25 WORKSTATION PARAMETERS 

Rinse air push: 25 Maximum elution volume: 12.0 mL

Elute air push: 5 Exhaust fan on: Y Y=Yes N=No 

Beeper on: N Y=Yes N=No 

Name Solvents

Solvent 1 : Water

Solvent 2 : Methanol 

Solvent 3 : Solvent 3 

Solvent 4 : Solvent 4 

Solvent 5 : Solvent 5 

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

66
Supplement B—Instructions for On-Site Processing 

Using Solid-Phase Extraction (SPE) 
INSTRUCTIONS FOR ON-SITE

PROCESSING USING 

SOLID-PHASE EXTRACTION (SPE)

1. Gather the equipment and supplies needed 

for on-site SPE listed in table 19. 

2. Record the precleaned SPE column type, 

lot number, and weight on the field 

form. Prepare the SPE column by

conditioning with about 2 mL of 

methanol, followed by about 2 mL of 

water to remove excess methanol. 

Allow the methanol and water to flow 

by gravity through the column. AT NO 

TIME SHOULD THE COLUMN GO 

DRY ONCE CONDITIONING HAS

STARTED (if it does, add methanol 

then water to recondition again). 

Maintain the water in the column bed 

by replacing the water that drains 

through, or by using an on-off valve to 

stop all water from draining out of the 

column. 

3. Tare the weight of the amber glass 1-L

sample bottle. Collect, split, and filter

samples using appropriate procedures 

(Sandstrom, 1995). Collect about 1 L

of the sample in the 1-L sample bottle

(do not completely fill the bottle; leave

about a 2-cm headspace to add 

conditioner and surrogate). 

4. Weigh and record the amount of sample 

collected. Add about 

10 mL of the methanol by using the 

bottle-top dispenser. Weigh and record

the sample-plus-methanol weight. 

5. Add the surrogate solution (1.25 ng/μL)

contained in the 2-mL amber screw-cap 

vial (refer to Spike Kit Instruction 

Manual for more detailed information 

on use of micropipet). Use the 100-μL

micropipet and a clean glass bore. 

Withdraw the solution into the glass 

bore, then put the tip into the sample

bottle, below the surface of the sample

(tip the bottle on the side if needed to 

reach below the surface with the tip of 

the micropipet), and press the plunger 

to deliver the surrogate to the sample. 

Withdraw the micropipet, remove and 

discard the glass bore, and rinse the 

orange-colored Teflon tip with 

methanol. Swirl the sample to mix. 

Detailed instructions on use of the 

micropipet are contained in the spike 

kit. 

6. Obtain a plastic 1-L beaker for collecting

the extracted water. 

7. If necessary, adjust the pump flow rate to 

20 to 25 mL/min by using the cleaning

solutions and graduated cylinder or 

beaker to measure volume. 

8. Insert the inlet end of the Teflon-PFA 

tubing from the SPE pump into the 

sample bottle. Turn on the pump and 

allow the air to be displaced from the 

Teflon tubing, then attach the Luer tip 

of the SPE column to the outlet end of

the pump tubing. Invert the column to 

discard any conditioning water 

remaining in the SPE reservoir and 

begin collecting extracted water that

passes through the column into the

plastic beaker. Pump sample through 

the column at 20 to 25 mL/min. After

sample has been pumped through 

column, turn off pump, disconnect SPE 

column, and record final weight of 

sample processed through the column. 

9. Remove excess water from SPE column 

by using a syringe to blow out water. 

Write sample ID on side of column, and 

store in 40-mL glass ampule. Store 

columns in cool place (between 4–

25oC). 

Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

68
CLEANING PROCEDURE

Clean all equipment after use by rinsing

with a laboratory detergent (Liquinox solution, 

0.2 percent), followed by rinses with about 30 

mL of tap water to remove the detergent; 

finally, rinse with about 30 mL of methanol. 

Wrap all openings of cleaned material with 

aluminum foil. 

Samples (and any materials added to 

samples) should contact only glass, Teflon, 

ceramic or stainless steel (or other metal). 

QUALITY-ASSURANCE SAMPLES 

Field equipment blank: Process a 

sample of pesticide-grade water (available

from NWQL, through One Stop Shopping)

1 

exactly as the samples. This includes 

sample bottles, compositing, splitting, and 

filtration equipment as well as the SPE 

system. Process the field-equipment blank 

at the start of sampling, and then after about 

every 10 to 15 samples. More frequent 

blanks are always helpful. 

Field matrix spikes: Collect duplicate

samples and add the 2.0-ng/μL-spike 

solution to one sample. Use the 100-μL

micropipet to add the spike solution, which 

is contained in a 2-mL glass vial, after about 

every 20 samples. Add the surrogate to 

every spiked sample. 

FURTHER INFORMATION 

Contact Frank Wiebe (e-mail – 

fwwiebe@usgs.gov; 303-236-3279), or 

Mark Sandstrom (e-mail – sandstro@usgs.gov; 

303-236-3943) for additional information. 

Table 19. Equipment and supplies required for broad spectrum pesticide analysis 

(methods 2010 and 2011) by on-site solid-phase extraction 

[mm, millimeter; in., inch; mL, milliliter; SPE, solid-phase extraction; μL, microliter; g, gram; 

μm, micrometer; mg, milligram; L, liter; ng/μL, nanogram per microliter] 

Number per 

sample 

Equipment

Filter Unit, 147-mm diameter, aluminum, and FMI Model QB-1 CKC pump and 1/4-in. 

diameter convoluted Teflon tubing

1 

Teflon squeeze bottle, 250 mL, for methanol 1 

Valveless, piston-type metering pump for SPE; FMI Model RHB 0CKC 1 

Fixed volume (100-μL) micropipet 1 

Portable balance (1,200.0 g) 1 

Filters, 147-mm diameter, 0.7-μm pore diameter, precleaned 1–5 

Bottle-top dispenser, 1–5 mL, for methanol (optional) 1 

Teflon squeeze bottle, 250 mL, for pesticide-grade water 1 

Supplies

SPE columns, International Sorbent Technologies Isolute C-18, 500 mg, precleaned1 1 

Sample bottles, 1-L, amber 1

Disposable glass bores, for 100-μL micropipet1 1 

Surrogate mixture, 1.25 ng/μL, 2-mL vial

1 1 

Liquinox detergent, 0.2-percent solution, 200 mL 1 

Pesticide-grade methanol, 200 mL 1 

Pesticide-grade water, 5 mL 1

Aluminum foil, roll 1

Gloves, disposable, nonpowdered, medium 1–5 

Spike kit, including Instruction Manual

1 1 

Spike mixture, 1–10 ng/μL, 2-mL vial

1 1 

1

Supplies obtained through WRD One Stop Shopping <http://1stop.usgs.gov>. 

Supplement B 69
Determination of Moderate-Use Pesticides and Selected Degradates in Water

by C-18 Solid-Phase Extraction and Gas Chromatography/Mass Spectrometry

70

Solid-Phase Extraction, GC/MS Analysis, Filtered Water 

Methods 2010 and 2011

Station ID or Unique Number: Station Name

Date: Time Collector:

Telephone Number of Collector:

Comments:

ON-SITE INFORMATION 

Filter Sample (0.7-μm glass fiber filter) Date filtered: 

Prior to filtration, record bottle tare wt. g

SPE Column Brand or Type:

Lot #:

Dry Wt.: g

 SPE Column Conditioning: Date of SPE procedure:

Methanol (2 mL): mL

Pesticide-grade water (2 mL): mL

 

(DO NOT LET COLUMN GO DRY ONCE CONDITIONING STARTED) 

 Sample Sample + bottle wt.: g

(-) bottle tare wt.: g

= Sample wt.: g

Add methanol conditioner (1% sample wt.): mL

Sample + bottle + methanol: g

Surrogate Solution ID:

Volume added: μL

QA Samples - Spike Mixture

Solution ID:

Volume added (100 μL): μL

 Sample through column:

Sample + plastic beaker: g

plastic beaker: g

 Flow rate: (=sample wt. extracted/time) mL/min

Start time: hr:min

Finish time: hr:min

Remove excess water — Write station IPD, date, time on column — Store in 40-mL vial @ 4°C 

NWQL INFORMATION 

Lab ID: Set #: Date Received

 Dry column with N2 or CO2: Date:

Pressure: lb/in2

Time: min

Dry SPE cartridge wt.: g

 SPE Elution Date:

Add 1.8 mL elution solvent (3:1) mL

 Internal Standard (PAH-dn mixture in toluene keeper)

Solution ID:

Volume added (100 μL): μL

 Evaporate solvent - nitrogen Date:

Pressure: lb/in2

Time: min

Analysis - Instrument ID: Date:

Comments: