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
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

By Steven D. Zaugg, Mark W. Sandstrom, Steven G. Smith,

 and Kevin M. Fehlberg

U.S. Geological Survey

Open-File Report 95-181

Denver, Colorado

1995

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U. S. GEOLOGICAL SURVEY

Gordon P. Eaton, Director

The use of brand, firm, and trade names in this report is for identification purposes only

and does not constitute endorsement by the U.S. Geological Survey.

For additional information Copies of this report can be

write to: purchased from:

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

U.S. Geological Survey Open-File Reports Section/ESIC

Box 25046, Mail Stop 407 Box 25286, Mail Stop 517

Federal Center Federal Center

Denver, CO 80225 Denver, CO 80225
i
ii
iii

CONTENTS

 Page 

Abstract 1

Introduction 1

Analytical Method 3

1. Scope and application 3

2. Summary of method 5

3. Interferences 5

4. Apparatus and instrumentation 5

5. Reagents and consumable materials 7

6. Sampling methods, sample-collection equipment, and

cleaning procedures 8

7. Standards 8

8. Gas chromatograph/mass spectrometer performance 10

8.1 Gas chromatograph performance evaluation 10

8.2 Mass spectrometer performance evaluation 10

9. Calibration 12

10. Procedure 15

11. Calculation of results 19

11.1 Qualitative identification 19

11.2 Quantitation 20

11.3 Reporting of results 21

Method performance 21

Conclusions 39

References cited 40

Supplement A--Automated solid-phase extraction procedure using

AutoTrace workstation 43

Supplement B--On-site solid-phase extraction procedure 45

FIGURES

Figure 1. Chromatograms showing: A, total ions of pesticides and

metabolites in 1.0-nanogram-per-microliter standard

solution; B, expanded view of the 21- to 28-minute

time interval shown in figure 1A 11

2. Diagram of manual solid-phase-extraction pumping

apparatus 16
iv

TABLES

 Page 

Table 1. Compound name, use, pesticide class, codes, and

registry numbers 4

2. Retention time, relative retention time, quantitation

ion, and confirmation ions for selected compounds,

surrogate compounds, and internal standards 13

3. Recovery and precision data from six determinations of

the compounds at 0.1 microgram per liter in

reagent water 23

4. Recovery and precision data from seven determinations

of the compounds at 1.0 microgram per liter in

reagent water 24

5. Recovery and precision data from seven determinations

of the compounds at 0.1 microgram per liter

in surface water (South Platte River near

Henderson, Colo.) 26

6. Recovery and precision data from seven determinations

of the compounds at 1.0 microgram per liter in

surface water (South Platte River near

Henderson, Colo.) 27

7. Recovery and precision data from seven determinations

of the compounds at 0.1 microgram per liter in

 ground water (Denver Federal Center Well 15) 29

8. Recovery and precision data from six determinations

of the compounds at 1.0 microgram per liter in

ground water (Denver Federal Center Well 15) 30

9. Method detection limit calculated from precision data

for seven determinations of the compounds

in reagent water fortified at initial detection limits

estimated in table 3 32

10. Summary of statistical data used to determine estimated

holding time of compounds on solid-phaseextraction columns held at 25 degrees Celsius 37

11. Equipment and supplies required for broad spectrum

pesticide analysis (Schedule 2010) by onsite

solid-phase extraction 49
v

CONVERSION FACTORS AND

ABBREVIATED WATER-QUALITY UNITS

Multiply By To obtain 

centimeter (cm) 3.94 x 10-1 inch

gram (g) 3.52 x 10-2 ounce

kilogram (kg) 3.53 x 10-1 ounce, avoirdupois

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

liter (L) 2.64 x 10-1 gallon

meter (m) 3.28 x 10o foot

microliter (μL) 2.64 x 10-7 gallon

micrometer (μm) 3.94 x 10-5 inch

milligram (mg) 3.53 x 10-5 ounce

milliliter (mL) 2.64 x 10-4 gallon

milliliter per minute (mL/min) 3.38 x 10-2 ounce per minute

millimeter (mm) 3.94 x 10-2 inch

nanogram (ng) 3.53 x 10-11 ounce

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

following equation:

oF = 9/5 (oC) + 32.

The following abbreviations are used in this report:

dc direct current ng/μL nanogram per microliter

μg/L microgram per liter lb/in2 pound per square inch

min minute V volt

ng/L nanogram per liter

The following terms are used in this report:

C-18 octadecyl PFA perfluoralkoxy

EDOC electronic documents system PFTBA perfluorotributylamine

ETFE ethylenetetrafluoroethylene SIM selected-ion monitoring

GC gas chromatography SPE solid-phase extraction

GCC glass bottle, amber USGS U.S. Geological Survey

GC/MS gas chromatograph/mass spectrometer

HIP hexane-isopropanol

HPLC high-performance liquid chromatography

ID inside diameter

MDL method detection limit

NAWQA National Water-Quality Assessment program

NWQL National Water Quality Laboratory

OD outside diameter

PAH polyaromatic hydrocarbon
vi
1

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

BY STEVEN D. ZAUGG, MARK W. SANDSTROM, STEVEN G. SMITH,

AND KEVIN M. FEHLBERG

ABSTRACT

A method for the isolation and analysis of 41 pesticides and pesticide

metabolites in natural-water samples is described. The pesticides are isolated

by C-18 solid-phase extraction and determined by capillary-column gas

chromatography/mass spectrometry with selected-ion monitoring. Water

samples are filtered to remove suspended particulate matter and then are

pumped through disposable solid-phase extraction columns containing

octadecyl-bonded porous silica to extract the pesticides. The columns are

dried using carbon dioxide or nitrogen gas, and adsorbed pesticides are

removed from the columns by elution with hexane-isopropanol (3:1).

Extracted pesticides are determined by capillary-column gas chromatography/

mass spectrometry with selected-ion monitoring of three characteristic ions.

The upper concentration limit is 4 micrograms per liter (μg/L) for most

pesticides, with the exception of widely used corn herbicides--atrazine,

alachlor, cyanazine, and metolachlor--which have upper concentration limits

of 20 μg/L. Single-operator method detection limits in reagent-water samples

range from 0.001 to 0.018 μg/L. Recoveries in reagent-water samples ranged

from 37 to 126 percent for most pesticides. The estimated holding time for

pesticides after extraction on the solid-phase extraction 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.

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 (Gianessi and others, 1986). They are frequently detected in

surface water and ground water in the United States (Hallberg, 1989) and

Europe (Leistra and Boesten, 1989). The traditional methods for determining

residues of pesticides in natural-water samples involve liquid-liquid
2

extraction with an organic solvent followed by analysis by gas chromatography (GC) with nitrogen-phosphorus or electron-capture detection, using

two columns to confirm pesticide identity.

Recently, methods for pesticide analysis using solid-phase extraction

(SPE) as an alternative to liquid-liquid extraction have been described (Bagnati

and others, 1988; Bellar and Budde, 1988; Eichelberger and others, 1988; Junk

and Richard, 1988; Battista and others, 1989; Brooks and others 1989; DiCorcia

and others, 1989; Sandstrom, 1989; Thurman and others, 1990). These SPE

methods are attractive because they are rapid, efficient, use less solvents than

liquid-liquid extraction, and consequently have lower laboratory expenses.

The SPE methods can be conducted onsite, which enables processing of

samples with labile compounds, or at remote sites. In addition, the SPE

methods can be automated by using laboratory robotic systems that do all or

part of the sample-preparation steps. Some of these SPE methods also

incorporate the use of a gas chromatograph/mass spectrometer (GC/MS)

operated under a selected-ion monitoring (SIM) mode for confirmation and

quantitation of pesticides. The GC/MS SIM is more specific than either the

nitrogen-phosphorus or electron-capture detector, and more sensitive than

the nitrogen-phosphorus detector.

This report describes a method for determining a broad range of

pesticides in natural-water samples. It was developed by the U.S. Geological

Survey (USGS) for use in the USGS National Water Quality Laboratory. The

method combines octadecyl (C-18) SPE for pesticide isolation and GC/MS

operated in the SIM mode for selective confirmation and quantitation of the

pesticides. It is rapid, more efficient, and can detect lower concentration

levels (in nanograms per liter) compared to other USGS methods (Wershaw

and others, 1987). The method supplements other methods of the USGS for

determination of organic substances in water that are described by Wershaw

and others (1987) and by Fishman (1993). The method was implemented in

the National Water Quality Laboratory (NWQL) in October 1992.

This report provides a detailed description of all aspects of the method,

including the equipment, reagents, sampling protocol, instrument

calibration, and SPE procedure required for sample analysis. Method

performance (precision and accuracy) and estimated method detection limits

for 47 pesticides are presented.

The scope of the report includes determination of method performance

in ultrapure water samples and two natural-water types--a ground water and

a surface water from the Denver, Colorado, region. Method performance was

determined at two concentration levels--0.1 and 1.0 μg/L--in each water type.

Method detection limits were determined according to an accepted statistical

procedure (U.S. Environmental Protection Agency, 1992). Holding times of

SPE columns before extraction and the use of an automated evaporation
3

system for solvent reduction also were evaluated. An optional on-site SPE

procedure is described, and an optional laboratory automated procedure is

briefly described in Supplements A and B to the report. The method was

tested on surface-water samples from the midcontinent of the United States

in 1991. During 1992, four study units of the National Water-Quality

Assessment (NAWQA) program tested the on-site isolation procedure.

ANALYTICAL METHOD

Organic Compounds and Parameter Codes: Pesticides, dissolved,

gas chromatography/mass spectrometry, O-1126-95 (see table 1)

1. Scope and application

This method is suitable for the determination of low-level

concentrations (in micrograms per liter and nanograms per liter) of pesticides

and pesticide metabolites in natural-water samples. The method is applicable

to pesticides and metabolites that are (1) efficiently partitioned from the water

phase onto an octadecyl (C-18) organic phase that is chemically bonded to a

solid inorganic 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 only for dissolved-phase

pesticides and metabolites.

The compounds include some of those in the NWQL Laboratory

Services Catalog (Timme, 1994), as well as newer pesticides determined to be

of national importance for the NAWQA program (table 1). The method was

developed in response to the request for a broad spectrum pesticide method

for use in determining their occurrence and distribution as monitored by the

NAWQA program. Pesticides were selected initially because of their

widespread use in the United States, according to information in Resources

for the Future database (Gianessi and Puffer, 1990, 1992a, and 1992b) and

compatibility with the general analytical plan. Other criteria included

published studies of pesticide fate and occurrence of metabolites, responses

from NAWQA Study Unit personnel regarding pesticides of local

significance, and U.S. Environmental Protection Agency health advisories.

Finally, restrictions in the analytical software on the number of ions scanned

for specific time intervals limited the number of pesticides chosen for testing

in the method to about 50.
4

Table 1.--Compound name, use, pesticide class, codes,and registry numbers

[NWQL, National Water Quality Laboratory; CAS, Chemical Abstract Service; MW, molecular weight; USE, annual

national use of active ingredient (a.i.) in thousand kilograms (kg) (a.i./1,000 kg, Gianessi and Puffer, 1990, 1992a, 1992b);

H, herbicide; AMID, Cl-acetamide; TRI, triazine; --, metabolite or pesticide no longer registered for use; MET, metabolite; I,

insecticide; OP, organophosphate; DNA, dinitroaniline; CB, carbamate; OC, organochlorine; UREA, phenyl urea; PYR,

permethrin; MISC, miscellaneous; URAC, uracil]

Compound

(common chemical name)

Use Class NWQL

code

Parameter

code

CAS

registry

number

MW

USE

(a.i/

1,000 kg)

Alachlor (Lasso) H AMID 4001 46342 15972-60-8 269.8 25,055

Atrazine H TRI 4003 39632 1912-24-9 215.7 29,163

Atrazine, desethyl-1 -- MET 4002 04040 6190-65-4 152.1 --

Azimphos-methyl (guthion)1 I OP 4004 82686 86-50-0 317.1 1,125

Benfluralin (Benefin) H DNA 4005 82673 1861-40-1 335.3 560

Butylate (Genate Plus, Suntan +) H CB 4006 04028 2008-41-5 217.4 8,675

Carbaryl (Sevin)1 I CB 4007 82680 63-25-2 201.2 44

Carbofuran (Furandan)1 I CB 4008 82674 1563-66-2 236.3 1,459

Chlorpyrifos I OP 4009 38933 2921-88-2 350.6 7,593

Cyanazine H TRI 4010 04041 21725-46-2 240.7 10,394

Dacthal (DCPA, chlorthal-dimethyl) H OC 4011 82682 1861-32-1 332.0 1,007

DDE, p,p'- I OC 4012 34653 72-55-9 318.0 --

Diazinon I OP 4013 39572 333-41-5 304.3 776

Dieldrin I OC 4015 39381 60-57-1 380.9 --

Diethylanaline, 2,6- -- MET 4016 82660 579-66-8 149.2 --

Dimethoate2 I OP 4017 82662 60-51-5 229.3 1,344

Disulfoton I OP 4018 82677 298-04-4 274.4 1,388

EPTC (Eptam) H CB 4019 82668 759-94-4 189.3 16,885

Ethalfluralin (Sonalan) H DNA 4020 82663 55283-68-6 333.3 1,597

Ethoprop (Mocap, ethoprophos) I OP 4021 82672 13194-48-4 242.3 743

Fonofos (Dyfonate) I OP 4022 04095 944-22-9 246.3 1,834

HCH, alpha- I OC 4023 34253 319-84-6 290.8 --

HCH, gamma- (Lindane) I OC 4025 39341 58-89-9 290.9 30

Linuron (Lorox, Linex) H UREA 4026 82666 330-55-2 249.1 1,191

Malathion I OP 4027 39532 121-75-5 330.3 1,447

Metolachlor (Dual) H AMID 4029 39415 51218-45-2 283.8 22,570

Metribuzin (Lexone, Sencor) H TRI 4030 82630 21087-64-9 214.3 2,189

Molinate (Ordram) H CB 4031 82671 2212-67-1 187.3 2,001

Napropamide (Devrinol) H AMID 4032 82684 15299-99-7 271.4 317

Parathion I OP 4033 39542 56-38-2 291.3 1,293

Parathion, methyl- (Penncap-M) I OP 4028 82667 298-00-0 263.2 3,692

Pebulate (Tillam) H CB 4034 82669 1114-71-2 203.3 296

Pendimethilan H DNA 4035 82683 40487-42-1 281.3 5,685

Permethrin, cis- I PYR 4036 82687 54774-45-7 391.3 509

Phorate (Thimet) I OP 4037 82664 298-02-2 260.4 2,171

Prometon H TRI 4039 04037 1610-18-0 225.3 --

Pronamide (Kerb) (Propyzamid) H AMID 4038 82676 23950-58-5 256.1 113

Propachlor (Ramrod) H AMID 4040 04024 1918-16-7 211.7 1,811

Propanil (Stampede) H AMID 4041 82679 709-98-8 218.1 3,412

Propargite (Omite) (alkyl sulfite) I MISC 4042 82685 2312-35-8 350.5 1,719

Simazine (Aquazine, Princep) H TRI 4043 04035 122-34-9 201.7 1,800

Tebuthiuron (Spike) H UREA 4045 82670 34014-18-1 228.3 276

Terbacil (Sinbar)1 H URAC 4046 82665 5902-51-2 216.7 175,

Terbufos (Counter) I OP 4047 82675 13071-79-9 288.4 3,277

Thiobencarb (Bolero) H CB 4044 82681 28249-77-6 257.8 617

Triallate (Avadex BW, Far-Go) H CB 4049 82678 2303-17-5 304.7 1,593

Trifluralin (Treflan) H DNA 4050 82661 1582-09-8 335.5 12,312

1These pesticides are qualitatively identified and reported with an E code (estimated value) because of problems with gas

chromatography or extraction.

2Pesticide shows small and variable recovery because of incomplete extraction. This pesticide was deleted from the

method in June 1994.
5

The calibration range is equivalent to concentrations from 0.001 to

4.0 μg/L for most pesticides. Widely and abundantly used corn herbicides--

atrazine, metolachlor, cyanazine, and alachlor--have upper concentration

limits of 20 μg/L. Method detection limit (MDL) is defined as the minimum

concentration of a substance that can be identified, measured, and reported

with 99-percent confidence that the compound concentration is greater than

zero (Wershaw and others, 1987). The MDL is compound dependent and

dependent on sample matrix and instrument performance and other

operational sources of variation. For the listed pesticides, MDLs vary from

0.001 to 0.018 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 in section 11.1), the result

is calculated and reported.

2. Summary of method

2.1 The samples are filtered at the collection site using glass-fiber filters

with 0.7-μm pore diameter to remove suspended particulate matter. The

procedure for filtration of samples for organic analysis is described by

Sandstrom (1995). Filtered water samples are pumped through disposable,

polypropylene SPE columns containing 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 carbon dioxide or nitrogen to

remove residual water. The adsorbed pesticides and metabolites then are

removed from the SPE columns by elution with hexane-isopropanol (3:1).

The eluant is further evaporated using a gentle stream of nitrogen. Extracts of

the eluant are analyzed by a capillary-column GC/MS operated in the SIM

mode.

3. Interferences

Organic compounds having gas-chromatographic retention times and

characteristic ions with a mass identical to those of the pesticides and

metabolites of interest may interfere.

4. Apparatus and instrumentation

4.1 Cleaning and elution module for SPE columns; Supelco, Inc.,

Visiprep Solid Phase Extraction Vacuum Manifold and Visidry Drying

Attachment or equivalent.

4.2 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
6

Metering Inc., Model QSY - 2 CKC or equivalent. For on-site SPE, an SPE

pump powered by a 12-V dc motor is needed; Fluid Metering Inc., Model

RHB - 0 CKC or equivalent.

4.3 Teflon-perfluoralkoxy (PFA) tubing, 3.18-mm OD; Cole-Parmer

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

4.4 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.

4.5 Pump control box (optional) for 12-V dc pumps, fitted with a

4-amp fuse, toggle switch, and 10-ohm 1.58-amp variable resistor.

4.6 Sample-preparation workstation (optional) for cleaning SPE

column; Zymark Inc., Benchmate Workstation or equivalent.

4.7 Bottle-top solvent dispenser, adjustable from 2 to 10 mL; Brinkman

Dispensette, Van Waters & Rogers (VWR) Scientific or equivalent.

4.8 Luer stopcocks (optional), flow control valves or on-off valves,

constructed of inert materials; Burdick & Jackson (B&J) Inert PTFE flow

control valve, Baxter Diagnostics, Inc. or equivalent.

4.9 Vacuum pump--Any vacuum pump with sufficient capacity to

maintain a slight vacuum of 1.5 to 3 kPa in the cleaning/elution module.

4.10 Micropipets--50- and 100-μL, fixed- and variable-volume

micropipets with disposable glass capillaries; VWR Scientific or equivalent.

4.11 Analytical balances--Capable of accurately weighing 1,200 g ±1 g and

10.000 g ±0.001 mg. An optional procedure for weighing the SPE columns

requires a balance capable of accurately weighing 10.000 g ±0.001 g.

4.12 Fused-silica capillary column that provides adequate resolution,

capacity, accuracy, and precision. A 25-m x 0.20-mm inside diameter (ID)

fused-silica capillary column coated with a 0.33-μm bonded film of

polyphenylmethylsilicone was used; Hewlett-Packard Ultra II or equivalent.

4.13 Automated solvent evaporator--The heat-bath temperature needs

to be maintained at 25°C, and the nitrogen gas pressure at 27.5 kPa (4 lb/in2);

Zymark Inc., TurboVap LV or equivalent.

4.14 GC/MS bench-top system; Hewlett-Packard, Model 5971 or

equivalent.
7

4.14.1 GC conditions: Oven, 100°C (hold 5 minutes), then program

to 300°C at 6°C/min, then hold for 5 minutes; injection port, 250°C; carrier

gas, helium; injection volume, 2 μL, splitless injection.

4.14.2 MS conditions: Interface, 290°C; source, 200°C; analyzer,

100°C; dwell time 20 milliseconds; mass ions monitored are listed in table 2

(see section 9, Calibration).

4.14.3 The apparatus and equipment required for the automated

SPE method are listed below; specific sources and models used during the

development of this method also are listed, where applicable:

4.14.3.1 AutoTrace SPE Workstation configured for

3-mL SPE columns; Zymark Inc. or equivalent. The set-up conditions and

processing steps for this method using the AutoTrace Workstation are listed

in Supplement B at the end of this report.

NOTE 1: 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.

5. Reagents and consumable materials

5.1 Helium carrier gas (99.999 percent) as contaminant free as possible.

5.2 Carbon dioxide gas for drying, ultrapure.

5.3 Nitrogen gas for evaporation, ultrapure.

5.4 SPE columns packed with 500 mg of silica coated with a chemically

bonded C-18 hydrocarbon phase and end-capped to reduce polar secondary

interactions associated with surface silanol groups, Isolute C-18 (EC) endcapped or equivalent; International Sorbent Technology, Ltd. or equivalent.

The solid packing material is held in place with stainless-steel frits.

NOTE 2: Similar columns obtained from Varian Sample Preparation

Products, Bond-Elut 1212-4025, were used during initial testing of the method

but were replaced by the Isolute columns because of their superior quality (see

Method Performance section).

5.5 Test tubes, borosilicate glass, 16 mm x 100 mm, baked at 450°C for

2 hours; Kimax Brand, VWR or equivalent.

5.6 Glass-fiber filters, 0.7-μm nominal pore diameter (GF/F grade),

baked at 450°C for 2 hours; Whatman, Inc. or equivalent.
8

5.7 Glass bottles, amber, 1,000-mL, 33-mm neck, baked at 450oC for 2

hours, fitted with Teflon-lined screw caps; NWQL GCC or equivalent.

5.8 Solvents: Hexane, toluene, isopropanol, methylene chloride, and

methanol; B&J Brand ultrapure pesticide quality or equivalent.

5.9 Reagent water, ultrapure, B&J Brand for HPLC or equivalent.

5.10 Detergent solution: Prepare a dilute mixture (0.2 percent) of

laboratory-grade phosphate-free liquid detergent; Liquinox, Alconox Inc. or

equivalent.

6. Sampling methods, sample-collection 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 U.S. Geological Survey for

obtaining depth- and width-integrated surface-water samples are given in

Edwards and Glysson (1988) and Ward and Harr (1990). Similar descriptions

of sampling methods for obtaining ground-water samples are given in Hardy

and others (1989).

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 metabolites from

the water. Material suitable for sample-collection equipment includes

fluorinated plastics (Teflon, ETFE), metals (stainless steel, aluminum), and

ceramics.

6.3 Cleaning procedures: Wash all sample-collection equipment with

phosphate-free detergent, rinse with distilled or tap water to remove all traces

of detergent, and finally rinse with ultrapure methanol (contained in a Teflon

squeeze-bottle). Clean all sample-collection equipment before each sample is

collected to prevent cross-contamination of the samples.

NOTE 3: Methanol needs to be collected and disposed of in accordance with

local regulations.

7. Standards

7.1 Stock standard solutions: Obtain the pesticides, metabolites,

internal standards, and surrogates as pure materials from commercial

vendors. If pure materials are obtained, prepare standard solutions of about
9

2,000 ng/μL by accurately weighing, to the nearest 0.001 mg, 10 mg of the pure

material in a 5-mL volumetric flask and dilute with ethyl acetate. Transfer

the stock solutions to clean vials and store in a refrigerator. The stock

solutions are stable for about 6 months.

7.2 Primary fortification standard solution (stock): Prepare a 40-ng/μL

concentration primary fortification standard solution by combining

appropriate volumes of the individual stock standard solutions in a 2- or

5-mL volumetric flask. Use adjustable micropipet (0-50 μL or 0-100 μL) to

dispense an appropriate volume into the volumetric flask and dilute with

toluene. Transfer the primary fortification standard solution to a clean vial

and store in a refrigerator. This solution is stable for about 6 months.

7.3 Primary dilution standard solution (working): Prepare lowconcentration (1 ng/μL) and high-concentration (10 ng/μL) primary dilution

standard solutions by combining appropriate volumes of the primary

fortification standard solution in a 2- or 5-mL volumetric flask and dilute

with methanol. Add a 100-μL aliquot of either primary dilution standard

solution to a 1-L water sample to obtain a concentration of 0.1 or 1 μg/L for

the method performance-evaluation studies.

7.4 Polyaromatic hydrocarbon (PAH) internal standard solution (stock):

Prepare a 50-ng/μL concentration of PAH internal standard solution by

combining appropriate volumes of the individual stock standard solutions of

acenapthalene-d10, phenanthrene-d10, and chrysene-d12 in a 2-mL volumetric

flask. Use an adjustable micropipet (0-100 μL) to dispense an appropriate

volume into the volumetric flask and dilute with toluene. Transfer the

primary dilution standard to a clean vial and store in a refrigerator. This

solution is stable for about 6 months.

7.5 PAH internal standard solution (working): Dilute part of the PAH

internal standard stock solution to 1 ng/μL. Use an adjustable micropipet

(0-100 μL) to dispense 100 μL into a 5-mL volumetric flask and dilute with

toluene. Transfer the PAH internal standard solution to a clean vial and

store in a refrigerator where it is stable for about 6 months.

7.6 Surrogate solution: Prepare a solution of Diazinon-d10, alpha-

 HCH-d6, and terbuthylazine from the stock standard solutions in methanol

at a concentration of 1 ng/μL.

7.7 Calibration solutions. Prepare a series of calibration solutions in

toluene that contain all pesticides and metabolites at concentrations from 0.01

to 40.0 ng/μL (0.01, 0.02, 0.04, 0.10, 0.20, 0.40, 1.0, 2.0, 4.0, 10, 20, 40 ng/μL) and

the PAH internal standard solution at a constant concentration of 1.0 ng/μL.

Prepare these calibration solutions by appropriate dilutions of the 10 and

40 ng/μL primary fortification and dilution standard solutions. For the
10

widely and abundantly used corn herbicides--atrazine, metolachlor,

cyanazine, and alachlor--prepare a calibration solution at a concentration of

200 ng/μL and the internal standard at 1.0 ng/μL. Prepare this calibration

solution by appropriate dilution of the stock standard solutions.

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 selected-compound (pesticide or

metabolite) response factors relative to response factors obtained using a new

capillary column and freshly prepared calibration solutions. An example of

the separation and peak shape of the pesticides and metabolites is shown in a

total ion chromatogram of a 1.0 ng/μL standard solution in figure 1. If peak

shape deteriorates or if response factors fail to meet the calibration criteria,

either change the injection liner or perform maintenance on 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 in response greater than 30 percent for pesticides and metabolites

susceptible to loss on injection--Linuron or Carbaryl--indicates a need for

immediate action.

8.2 Mass spectrometer performance evaluation

8.2.1 Check the mass spectrometer prior to analysis for the presence

of water and air which indicate leaks in the vacuum. If detected, locate and

fix leaks. Also, check the instrument every 24 hours during a series of

analyses to ensure mass spectrometer performance according to the perfluorotributylamine (PFTBA) tuning criteria outlined below. In addition, initially

adjust the mass spectrometer to ensure that the established reporting level for

each selected compound can be achieved.

8.2.2 Tune the mass spectrometer daily 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. Adjust the electron multiplier voltage to

get an area of 2,000,000 counts for the mass 69 ion. Manually adjust the

resolution so that the mass 69 ion has 100 percent abundance, mass 219 ion is

40±20 percent, and mass 414 ion is 6.2±5.7 percent relative abundance. Check

mass assignments to ensure accuracy to ±0.15 atomic mass unit and that mass

peak widths measured at one-half the peak height range from about 0.53 to

0.59 atomic mass unit.
11

34.900

23.663

ABUNDANCE OF ION COUNTS

400,000

300,000

200,000

100,000

0

15 20 25 30 35 40

TIME, IN MINUTES

40,000

50,000

30,000

20,000

10,000

0

21 22 23 24 25 26 27 28

Figure 1.--A, Chromatogram of total ions of pesticides and metabolites in 1.0-nanogram-per-microliter

standard solution; B, expanded view of the 21- to 28-minute time interval shown in figure 1A.

Retention times shown above each peak correspond to compounds listed in table 2. 13.477 14.192 15.966 16.695 17.364 18.089 18.506 20.148 20.558 28.413 30.101 30.507 30.721 33.567

35.992

37.637

37.841

21.437

21.819

21.044

21.151

21.354

22.661

22.741

22.696

22.877

23.341

23.436

23.615 23.555

23.806

24.044

24.235

24.354

25.333

25.321

25.631

25.858

25.846

26.730

26.861

26.944

27.171

27.290

27.338 27.493

21.926

22.069

22.571

A

B

Section

expanded

below

23.410
12

Calibration

9.1 Acquire initial calibration data by using a new capillary column and

freshly prepared calibration solutions. Use these data in subsequent

evaluation of the GC/MS performance.

9.2 Prior to the analysis of each sample set and every 10 samples

thereafter during a series of analyses, analyze and evaluate a calibration

solution (or solutions) containing all of the selected compounds to ensure

that the GC/MS performance is in compliance with the established criteria.

9.3 Acquire data for each calibration solution by injecting 2 μL of each

solution into the GC/MS according to the GC/MS conditions already

described. Calculate the relative retention time for each selected compound

and the surrogate compounds (RRTc) in the calibration solution or in a

sample as follows:

RRTc = 

RTc

RTi

 (1)

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 (acenapthalene-d10, phenanthrene-d10, or 

chrysene-d12, table 2).

9.4 Calculate a response factor (RFc) for each selected compound and

the surrogate compounds in each calibration solution as follows:

RFc = Ac x Ci

Cc x Ai

 (2)

where Ac = GC peak area of the quantitation ion for the selected compound 

or surrogate compounds;

Ci = concentration of the internal standard, in nanograms per 

microliter;

Cc = concentration of the selected compound or surrogate 

compounds, in nanograms per microliter; and

Ai = GC peak area of the quantitation ion for the internal standard.

9.5 See table 2 for the respective quantitation ions and internalstandard reference used in these calculations.
13

Table 2.--Retention time, relative retention time, quantitation ion, and

confirmation ions for selected compounds, surrogate compounds,

and internal standards

[Compounds are listed in order of retention time. min, minutes; m/z, mass per unit charge;

IS, internal standard; --, not used]

Compound

Retention

time

(min)

Relative

retention

time

Quantitation

ion

(m/z)

Second

confirmation ion

(m/z)

Third

confirmation ion

(m/z)

Internal

standard

reference

Diethylanaline, 2,6- 13.477 0.766 134 149 119 IS1

EPTC 14.191 .817 128 132 189 IS1

Butylate 15.966 .919 146 156 174 IS1

Pebulate 16.695 .962 128 57 132 IS1

Tebuthiuron 18.089 1.042 156 171 88 IS1

Molinate 18.506 1.066 126 187 55 IS1

Ethalfluralin 20.044 .889 276 316 292 IS2

Ethoprop 20.558 .869 158 200 97 IS2

Propachlor 21.148 1.160 120 176 93 IS1

Atrazine, desethyl- 21.151 .894 172 174 187 IS2

Trifluralin 21.354 .902 306 264 248 IS2

Benfluralin 21.437 .906 292 318 264 IS2

Phorate 21.819 .922 75 121 231 IS2

HCH, alpha- 22.069 .933 181 183 219 IS2

Dimethoate 22.571 .954 125 87 93 IS2

Prometon 22.661 .958 210 183 225 IS2

Simazine 22.696 .959 201 186 173 IS2

Carbofuran 22.741 .961 164 149 127 IS2

Atrazine 22.877 .967 200 173 138 IS2

HCH, gamma- 23.341 .986 183 181 109 IS2

Terbufos 23.436 .990 153 186 231 IS2

Pronamide 23.555 .989 175 173 145 IS2

Fonofos 23.615 .997 109 137 246 IS2

Diazinon 23.805 1.006 137 179 153 IS2

Disulfoton 24.044 1.016 88 153 186 IS2

Terbacil 24.235 1.027 161 117 - - IS2

Triallate 24.354 1.029 86 268 145 IS2

Propanil 25.321 1.072 161 163 217 IS2

Metribuzin 25.333 1.072 198 199 144 IS2

Parathion-methyl 25.631 1.083 109 125 263 IS2

Carbaryl 25.846 1.092 144 115 116 IS2

Alachlor 25.858 1.093 160 188 237 IS2

Linuron 26.730 1.130 61 160 248 IS2

Malathion 26.861 1.135 173 127 125 IS2

Thiobencarb 26.944 1.139 100 257 125 IS2

Metolachlor 27.171 1.148 162 238 240 IS2

Cyanazine 27.278 1.153 225 240 173 IS2
14

Table 2.--Retention time, relative retention time, quantitation ion, and

confirmation ions for selected compounds, surrogate compounds, and

internal standards--Continued

Compound

Retention

time

(min)

Relative

retention

time

Quantitation

ion

(m/z)

Second

confirmation ion

(m/z)

Third

confirmation ion

(m/z)

Internal

standard

reference

Chlorpyrifos 27.290 1.153 197 199 314 IS2

Parathion 27.338 1.165 109 291 125 IS2

Dacthal 27.493 1.162 301 299 332 IS2

Pendimethalin 28.413 .814 252 281 162 IS3

Napropamide 30.101 .862 128 171 271 IS3

DDE, p,p'- 30.506 .874 246 248 318 IS3

Dieldrin 30.721 .880 79 263 265 IS3

Propargite 33.567 .962 135 173 81 IS3

Azimphos-methyl 35.992 1.034 160 132 77 IS3

Permethrin, cis- 37.637 1.078 183 163 165 IS3

Surrogates 

HCH-d6, alpha- 21.926 0.927 224 222 226 IS2

Terbuthylazine 23.412 .989 173 138 231 IS2

Diazinon-d10 23.663 1.363 138 153 183 IS2

Internal Standards 

Acenapthalene-d10

(IS1)

17.364 1 162 164 160 - -

Phenanthrene-d10

(IS2)

23.663 1 188 - - - - - -

Chrysene-d12 (IS3) 34.900 1 240 - - - - - -

9.6 Initial calibration data acquired using a new capillary column and

fresh calibration solutions are acceptable if the relative standard deviation is

less than or equal to 35 percent for response factors calculated across the

working concentration range for each selected compound or surrogate

compounds.

NOTE 4: The concentration range suitable for the quantitation of pesticides

and metabolites in this method is from 0.01 to 40 ng/μL, equivalent to 0.001 to

4.0 μg/L in a 1-L sample. Atrazine, alachlor, metolachlor, and cyanazine have

an additional higher concentration standard solution, resulting in a high

concentration quantitation limit of 20 μg/L.

9.7 Subsequent daily response factors calculated for the majority of

compounds need to agree within ±20 percent of the average response factor

for the selected compound of interest. Analyze at least one calibration

solution with each sample set, and analyze a standard near or at the detection

limit at least once weekly to verify that the detection limits are being

achieved.
15

9.8 Add the latest response factors to prior response factors and

calculate a new average response factor, provided the latest data meet the

criteria given above, and the relative standard deviation for all of the

response-factor data is less than or equal to 35 percent.

9.9 Calibration-curve fitting routines also can be used, provided back

calculation of the calibration-standard concentration agrees within ±20

percent of the expected value.

10. Procedure

10.1 Weighing SPE columns (optional): Weigh the SPE columns

(±0.0001 g) and record the weight on the column using waterproof ink.

NOTE 5: Recording the weight on the SPE columns helps to determine when

the columns are dry after extraction and drying steps.

10.2 Precleaning SPE columns: Preclean the SPE columns by rinsing

with 3 mL of the elution solvent (hexane-isopropanol 3:1). Allow the solvent

to drain by gravity, then completely remove all solvent from the column by

either nitrogen positive pressure or vacuum. Use a vacuum/elution

apparatus to remove solvent by vacuum. Attach the SPE columns to the

Luer-Lok fittings and twist counterclockwise to open the fittings. An optional

Benchmate Workstation also can be used for automated cleaning of the

columns in batches of 50. Store the clean columns in 40-mL glass vials until

used.

10.3 Precleaning extraction apparatus: Set up the solid-phase-extraction

pumping apparatus as shown in figure 2. 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 100 mL of tap water and 50 mL of

methanol. Turn on the pump and adjust the flow rate of the pump to 20 to

25 mL/min using a graduated cylinder to measure the volume through the

SPE column. Ensure there are no leaks in any of the fittings. Keep the clean

inlet tubing of the pump in the glass cylinder to avoid contamination of the

tubing while preparing the sample and SPE column. For longer storage, wrap

the tubing in aluminum foil.
16

+ -

BATTERY

(12-Volt Direct 

Current)

 CERAMIC-PISTON

METERING PUMP

 TEFLON-FEP

TUBING 

(3.18-millimeter outside 

diameter) 

TUBE FITTING (3.18-

to 6.35-millimeter pipe thread)

EXTRACTED SAMPLE

FILTERED SAMPLE

TUBE

UNION

Tefzel Female

Luer Connector

Tefzel Union

(3.18 millimeter)

Tefzel Nut

Teflon Tubing

(3.18-millimeter 

outside diameter)

1/4-28

Thread

SPE

CARTRIDGE

Figure 2.--Manual solid-phase-extraction pumping apparatus.
17

10.4 SPE column conditioning: Immediately before sample extraction,

add 3 mL of methanol to the SPE column and allow the methanol to partially

drain 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. This conditioning ensures maximum interaction of the C-18 phase with the sample.

NOTE 6: Do not allow the columns to go dry once conditioning has started.

Maintain levels of fluids by adding additional fluid or by closing Luer-Lok

fittings or flow-control values.

10.5 SPE column equilibration: Replace the methanol in the SPE

column with ultrapure water to equilibrate the column with the sample

matrix. Add 3 mL of ultrapure water and allow the water and methanol to

partially drain through the column by gravity. About 5 minutes is required

for each volume of the water and methanol to drip through the column.

10.6 Sample preparation: Water samples must have been previously

filtered (Sandstrom, 1995). Weigh the sample and bottle and record the gross

sample weight (±1 g). To the sample, add methanol equivalent to 1 percent of

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

sample weight. Add a 100-μL aliquot of the surrogate solution (1 ng/μL)

using a micropipet with a disposable glass bore. (This should result in a

concentration of 0.1 μg/L for the surrogates in a 1-L sample.) Swirl the

sample in the bottle to thoroughly mix.

NOTE 7: Allow surrogate and spike solutions to come to room temperature

before adding to samples.

10.7 Sample extraction: Weigh a 1,000-mL plastic beaker 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 tubing end is positioned in 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 through the column.

NOTE 8: To avoid contaminating the sample, do not handle the outside of

the clean section of tubing that is placed in the sample bottle. A piece of tape

attached to the top of the tubing helps to indicate which section of the tubing

can be handled and which is clean and will be in contact with the sample.
18

10.8 Pump all of the sample through the SPE column and turn off the

pump when completed. Disconnect the column from the pump system and

remove residual interstitial water with a positive pressure of air. Weigh the

extracted water sample, and record the final weight of the sample processed

through the column. Discard the extracted sample, weigh the empty sample

bottle, and record the tare weight.

10.9 Clean the pump and Teflon-PFA tubing with detergent solution,

water, and methanol (see section 6.3) to prepare for the next sample.

10.10 SPE column drying: Attach a universal adapter to the large, open

end of the SPE column. Next attach the adapter to the male Luer-Lok fitting

on the gas-pressure module of the SPE vacuum manifold, and then dry the

column using a positive pressure (138 kPa or 20 lb/in2 for 20 minutes) of

ultrapure carbon dioxide to remove all interstitial water. Ultrapure nitrogen

gas also can be used to dry the column, but the drying time might be longer.

Optional: Verify that all water is removed from the column by periodically

weighing the column and comparing the weight to the pre-extraction weight.

NOTE 9: Do not dry the column for excessive periods of time. Pesticides and

metabolites might evaporate and be removed in the gas phase.

10.11 Elution of compounds: Label a 16- x 100-mm culture tube with

sample identification and place in a holding rack. Add 100 μL of the internal

standard PAH solution (1 ng/μL) 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 rests on the edge of the culture tube, keeping the

male Luer end of the SPE column raised a few centimeters above the bottom

of the culture tube. Add 3 mL of HIP (3:1) to the SPE column and allow the

solvent to drain by gravity into the culture tube (about 5 minutes). Air

pressure (using a 50-mL glass syringe) can be used to gently force interstitial

solvent remaining in the column into the vial.

10.12 Evaporation of solvent: Preheat the TurboVap evaporator water

bath to 30°C, and adjust the gas pressure to 34.5 kPa (5 lb/in2). Place culture

tubes in the TurboVap evaporator for about 15 minutes and 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 might result in loss of compounds.

10.13 Transfer to vials: Using a baked disposable glass Pasteur pipet,

withdraw eluant into pipet, and transfer eluant to appropriately labeled GC

vial containing a 200-μL insert for GC/MS analysis.
19

NOTE 10: A glass syringe fitted with a short length of silicone tubing to attach

the glass Pasteur pipet is the preferred procedure for withdrawing eluant into

the pipet. Solvent vapors in contact with rubber or latex pipet bulbs might

contaminate the eluant with plasticizers.

10.14 Rinse the culture tube with 50 μL of toluene, using a syringe to

dispense the solvent, and taking 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 3-mL solvent volume. Transfer the toluene rinse into

the GC vial insert. Cap GC vial, and refrigerate until analysis by GC/MS.

NOTE 11: Using a pipet or squeeze bottle to rinse the culture tube is not good

practice because this might result in excess solvent added and require

additional evaporation.

10.15 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 solutions. Prior to

the analysis of any sample extracts, ensure that the PFTBA mass-spectral

performance criteria have been met, and that the selected-compound

calibration data conform to the criteria set forth above. In addition, optimize

the system so the reporting level for each selected compound can be achieved.

Inject 2 μL of the sample extract and acquire data using the GC/MS conditions

described in sections 4.14.1 and 4.14.2.

11. Calculation of results

11.1 Qualitative identification

11.1.1 The expected retention time (RT) 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 based on the RRTc obtained from the

internal-standard analysis. Calculate the expected retention time as follows:

RT = RRTc x RTi (3)

where RT = expected retention time of the selected compound

or surrogate compound,

RRTc = relative retention time of the selected compound

or surrogate compound, and

RTi = uncorrected retention time of the quantitation ion

of the internal standard.
20

11.1.2 Mass-spectral verification for each selected compound is done

by comparing the relative integrated abundance values of the three significant

ions monitored with the relative integrated abundance values obtained from

calibration solutions analyzed by the GC/MS according to procedures given

above. The relative ratios of the three ions need to be within ±20 percent of

the relative ratios of those obtained on injection of a 1-ng 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

 (4)

where W = weight of sample, in grams;

W a = weight of sample and 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, calculate the concentration in the sample as

follows:

C = Ci x Ac x 1000

Fc x Ai x W (5)

where C = concentration of the selected compound or surrogate

compound in the sample, in micrograms per liter;

Ci = mass of the corresponding internal standard,

in micrograms per sample;

Ac = area of the quantitation ion for the selected

compound or surrogate compound identified;

Fc = response factor for each selected compound or

surrogate compound calculated above;

Ai = area of the quantitation ion for the internal standard; and

W = volume of the sample, in milliliters (assume 1.0 g = 1.0 mL).
21

11.2.3 The percent recovery of the surrogate compounds is

calculated as follows:

R = Ci x Ac

RFc x Ai x Cs x Vs

 x 100 (6)

where R = percent recovery of the surrogate compound;

Ci = mass of the corresponding internal standard,

in nanograms per sample;

Ac = area of the quantitation ion for the surrogate compound;

RFc = response factor for the surrogate compound;

Ai = area of the quantitation ion for the internal standard;

Cs = concentration of the surrogate compound in the surrogate 

standard solution added to the sample, in nanograms 

per microliter; and

Vs = volume of the surrogate standard solution added

to the sample, in microliters.

11.3 Reporting of results

This method was designed for use in studies of pesticide occurrence

and transport, for which the best possible information about the presence and

concentration of a pesticide is needed even if the standard error is relatively

high. Consequently, results are not censored at a low reporting level.

Concentrations of pesticides are reported as follows: If the concentration is

less than the MDL listed in table 9, report the concentration to three

significant figures, using the "E" code to alert the user that the result is less

than the statistically determined MDL; if the concentration is greater than the

detection limit, report the concentration to three significant figures; if the

concentration is greater than the highest concentration standard, report the

result as "greater than the highest standard," for example, >4 μg/L.

METHOD PERFORMANCE

A reagent-water sample, a surface-water sample collected from the South

Platte River near Henderson, Colo., and a ground-water sample collected in

Jefferson County, Colo. (monitoring well near building 15, Denver Federal

Center) were used to test the method performance. Each of the three samples

was split into 14 1-L subsamples. One set of seven subsamples was fortified

with 0.1 μg/L of each compound and the other set of seven subsamples was

fortified with 1.0 μg/L of each compound. 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 in

one laboratory (the National Water Quality Laboratory) using one GC/MS.
22

Each sample set was extracted and analyzed on different days during

September 1992, so comparison of different matrices and concentrations

includes bias from day-to-day variation. Accuracy and precision data from the

analyses are listed in tables 3 through 8.

Rejection of outlier samples: If the concentration of more than one

replicate determination from a subsample was consistently high or low, it was

assumed there was a systematic error with that sample, and the data were not

included in calculating the method performance. One replicate was rejected

in both the 0.1-μg/L concentration in the reagent-water data set and in the 1.0-

μg/L concentration in the ground-water data set, so only six replicates were

used to evaluate method performance.

Rejection of individual compound outliers: If the relative standard

deviation for any concentration-matrix specific data set was greater than

10 percent, extreme values were tested as outliers using a standard Student's

t-test (American Society for Testing and Materials, 1993). Outliers were

rejected if the t-value exceeded the critical t-value [t = 2.14, 7 degrees of

freedom, α=0.01 (99-percent confidence level)]. Using this approach, two

results were rejected as outliers (tables 4 and 9).

Corrections for background concentrations: The ground-water sample

did not require correction for background concentrations of compounds. The

surface-water sample contained low concentrations of atrazine (0.043 μg/L),

simazine (0.022 μg/L), Terbufos (0.059 μg/L), pronamide (0.074 μg/L),

Diazinon (0.062 μg/L), Carbaryl (0.18 μg/L), and tebuthiuron (0.12 μg/L).

These concentrations are subtracted from values determined to give corrected

results in tables 5 and 6.

Method detection limits: The MDL is defined as the minimum

concentration of a substance that can be identified, measured, and reported

with 99-percent confidence that the compound concentration is greater than

zero (Wershaw and others, 1987). MDLs were determined according to

procedures outlined by the U.S. Environmental Protection Agency (1992).

Seven replicate samples of reagent water fortified at 0.1 μg/L were analyzed to

determine a preliminary estimated MDL (table 3).

The MDL was calculated using the following equation:

MDL = S x t(n–1, 1–α= 0.99) (

where S = standard deviation of replicate analyses, in

micrograms per liter, at the lowest concentration;

n = number of replicate analyses; and

t(n–1, 1–α = 0.99) = Student's t-value for the 99-percent confidence level

with n–1 degrees of freedom (U.S. Environmental

Protection Agency, 1992).
23

Table 3.--Recovery and precision data from six determinations of the

compounds at 0.1 microgram per liter in reagent water

[conc., concentration; μg/L, microgram per liter; MDL, method detection limit;

E code, estimated value; --, MDL not determined for surrogates]

Compound

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Preliminary

estimated

MDL

(μg/L)

Alachlor 0.086 0.003 3 86 0.009

Atrazine .089 .005 6 89 .017

Benfluralin .046 .004 9 46 .013

Butylate .080 .002 3 80 .008

Chlorpyrifos .083 .002 2 83 .005

Cyanazine .096 .004 4 96 .013

Dacthal .082 .001 2 82 .004

DDE, p,p'- .048 .003 6 48 .010

Diazinon .077 .002 3 77 .008

Dieldrin .067 .003 4 67 .008

Diethylanaline, 2,6- .073 .002 3 73 .006

Disulfoton .072 .003 4 72 .008

EPTC .080 .002 2 80 .005

Ethalfluralin .054 .004 8 54 .013

Ethoprop .080 .004 5 80 .012

Fonofos .075 .002 3 75 .008

HCH, alpha- .077 .002 3 77 .007

HCH, gamma- .077 .003 4 77 .011

Linuron .126 .012 10 126 .039

Malathion .090 .005 5 90 .014

Metolachlor .092 .003 3 92 .009

Metribuzin .042 .004 9 42 .012

Molinate .082 .002 3 82 .007

Napropamide .083 .003 4 83 .010

Parathion .083 .007 9 83 .022

Parathion-methyl .073 .011 15 73 .035

Pebulate .079 .003 4 79 .009

Pendimethalin .046 .006 13 46 .018

Permethrin, cis- .037 .005 13 37 .016

Phorate .077 .003 4 77 .011

Prometon .077 .003 3 77 .008

Pronamide .076 .003 4 76 .009

Propachlor .079 .005 6 79 .015

Propanil .096 .005 5 96 .016

Propargite .059 .002 3 59 .006

Simazine .076 .003 3 76 .008

Tebuthiuron .088 .005 6 88 .015

Terbufos .074 .004 5 74 .012

Thiobencarb .085 .003 3 85 .008

Triallate .075 .003 4 75 .008

Trifluralin .047 .004 8 47 .012
24

Table 3.--Recovery and precision data from six determinations of the

compounds at 0.1 microgram per liter in reagent water--Continued

Compound

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Preliminary

estimated

MDL

(μg/L)

Pesticides having poor performance and reported with an E code

Atrazine, desethyl- 0.012 0.001 8 12 0.003

Azimphos-methyl .078 .012 15 78 .038

Carbaryl .151 .014 10 151 .046

Carbofuran .108 .004 4 108 .013

Terbacil .075 .010 13 75 .030

Pesticide deleted from method in November 1994 

Dimethoate 0.011 0.008 68 11 0.024

Surrogates 

HCH-d6, alpha- 0.905 0.015 2 90 - -

Diazinon-d10 .876 .024 3 88 - -

Terbuthylazine 1.000 .022 2 100 - -

Table 4.--Recovery and precision data from seven determinations of the

compounds at 1.0 microgram per liter in reagent water

[conc., concentration; μg/L, microgram per liter; E code, estimated value]

Compound

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Alachlor 0.861 0.039 5 86

Atrazine .840 .046 5 84

Benfluralin .483 .033 7 48

Butylate .769 .035 5 77

Carbaryl 2.020 .204 10 202

Carbofuran 1.261 .066 5 126

Chlorpyrifos .784 .053 7 78

Cyanazine .901 .047 5 90

Dacthal .829 .046 6 83

DDE, p,p'- .371 .049 13 37

Diazinon .779 .041 5 78

Dieldrin .600 .030 5 60

Diethylanaline, 2,6- .694 .038 6 69

Disulfoton .757 .034 5 76

EPTC .780 .035 5 78

Ethalfluralin .532 .035 7 53
25

Table 4.--Recovery and precision data from seven determinations of the

compounds at 1.0 microgram per liter in reagent water--Continued

Compound

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Ethoprop 0.793 0.027 3 79

Fonofos .777 .033 4 78

HCH, alpha- .739 .030 4 74

HCH, gamma- .766 .032 4 77

Linuron1 1.173 .032 3 117

Malathion .961 .047 5 96

Metolachlor .891 .044 5 89

Metribuzin .345 .018 5 35

Molinate .753 .027 4 75

Napropamide .718 .027 4 72

Parathion .905 .056 6 90

Parathion-methyl .924 .052 6 92

Pebulate .762 .032 4 76

Pendimethalin .521 .036 7 52

Permethrin, cis- .343 .064 19 34

Phorate .737 .028 4 74

Prometon .671 .046 7 67

Pronamide .842 .042 5 84

Propachlor .786 .028 4 79

Propanil .908 .048 5 91

Propargite .506 .050 10 51

Simazine .612 .033 5 61

Tebuthiuron1 .936 .052 6 94

Terbufos .714 .033 5 71

Thiobencarb .841 .047 6 84

Triallate .733 .038 5 73

Trifluralin .489 .033 7 49

Pesticides having poor performance and reported with an E code 

Atrazine, desethyl- 0.091 0.006 6 9

Azimphos-methyl .889 .051 6 89

Carbaryl 2.020 .204 10 202

Carbofuran 1.261 .066 5 126

Terbacil .577 .032 6 58

Pesticide deleted from method in November 1994 

Dimethoate 0.052 0.005 10 5

Surrogates 

HCH-d6, alpha- 0.954 0.042 4 95

Diazinon-d10 1.002 .058 6 100

Terbuthylazine 1.075 .060 6 107

1Six replicates were used for accuracy and precision data after rejection of one concentration (linuron, 1.400 μg/L; tebuthiuron, 0.465 μg/L) as an outlier based on Student's

t-test (American Society for Testing and Materials, 1993).
26

Table 5.--Recovery and precision data from seven determinations

of the compounds at 0.1 microgram per liter in surface water

(South Platte River near Henderson, Colo.)

[conc., concentration; μg/L, microgram per liter; --, no data; E code, estimated value]

Compound

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Alachlor 0.095 0.006 6 95

Atrazine1 .060 .007 12 60

Benfluralin .060 .006 9 60

Butylate .085 .010 11 85

Chlorpyrifos .080 .008 10 80

Cyanazine .066 .003 5 66

Dacthal .087 .007 8 87

DDE, p,p'- .045 .007 15 45

Diazinon1 .068 .009 13 68

Dieldrin .062 .005 9 62

Diethylanaline, 2,6- .067 .006 9 67

Disulfoton .141 .005 3 141

EPTC .083 .004 5 83

Ethalfluralin .068 .006 9 68

Ethoprop .096 .011 12 96

Fonofos .073 .005 7 73

HCH, alpha- .077 .005 7 77

HCH, gamma- .072 .005 7 72

Linuron .037 .002 5 37

Malathion .085 .006 7 85

Metolachlor .087 .004 5 87

Metribuzin .056 .004 7 56

Molinate .081 .004 5 81

Napropamide .079 .004 5 79

Parathion .068 .006 8 68

Parathion-methyl .071 .006 8 71

Pebulate .081 .004 5 81

Pendimethalin .064 .004 7 64

Permethrin, cis- .039 .006 16 39

Phorate .105 .005 5 105

Prometon .098 .011 11 98

Pronamide1 .046 .010 22 46

Propachlor .082 .006 7 82

Propanil .083 .008 10 83

Propargite .056 .005 9 56

Simazine1 .058 .005 8 58

Tebuthiuron1 -- -- -- --

Terbufos .046 .004 9 46

Thiobencarb .076 .006 8 76

Triallate .071 .005 7 71

Trifluralin .063 .004 7 63
27

Table 5.--Recovery and precision data from seven determinations

of the compounds at 0.1 microgram per liter in surface water

(South Platte River near Henderson, Colo.)--Continued

Compound

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Pesticides having poor performance and reported with an E code

Atrazine, desethyl- 0.019 0.002 9 19

Azimphos-methyl .042 .006 14 42

Carbaryl .010 .032 335 10

Carbofuran .119 .006 5 119

Terbacil .125 .010 8 125

Pesticide deleted from method in November 1994 

Dimethoate 0.034 0.006 17 34

Surrogates 

HCH-d6, alpha- 0.844 0.044 5 84

Diazinon-d10 .851 .057 7 85

Terbuthylazine .789 .042 5 79

1Corrected for background concentrations of compound in surface water.

Table 6.--Recovery and precision data from seven determinations

of the compounds at 1.0 microgram per liter in surface water

(South Platte River near Henderson, Colo.)

[conc., concentration; μg/L, microgram per liter; E code, estimated value]

Compound

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Alachlor 0.827 0.036 4 83

Atrazine1 .769 .028 4 77

Benfluralin .619 .058 9 62

Butylate .853 .023 3 85

Chlorpyrifos .671 .040 6 67

Cyanazine .629 .034 5 63

Dacthal .821 .035 4 82

DDE, p,p'- .397 .051 13 40

Diazinon1 .763 .027 4 76

Dieldrin .577 .045 8 58

Diethylanaline, 2,6- .738 .018 2 74

Disulfoton .746 .020 3 75

EPTC .861 .022 3 86

Ethalfluralin .645 .046 7 65
28

Table 6.--Recovery and precision data from seven determinations

of the compounds at 1.0 microgram per liter in surface water

(South Platte River near Henderson, Colo.)--Continued

Compound

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Ethoprop 0.835 0.028 3 84

Fonofos .738 .019 3 74

HCH, alpha- .654 .016 2 65

HCH, gamma- .756 .022 3 76

Linuron .257 .023 9 26

Malathion .761 .037 5 76

Metolachlor .880 .033 4 88

Metribuzin .430 .017 4 43

Molinate .845 .024 3 85

Napropamide .803 .010 1 80

Parathion .680 .032 5 68

Parathion-methyl .619 .030 5 62

Pebulate .864 .023 3 86

Pendimethalin .647 .054 8 65

Permethrin, cis- .316 .047 15 32

Phorate .742 .018 2 74

Prometon .670 .061 9 67

Pronamide1 1.147 .040 3 115

Propachlor .816 .035 4 82

Propanil .770 .031 4 77

Propargite .566 .067 12 57

Simazine1 .657 .028 4 66

Tebuthiuron1 .653 .060 9 65

Terbufos .696 .025 4 70

Thiobencarb .761 .029 4 76

Triallate .703 .022 3 70

Trifluralin .635 .057 9 64

Pesticides having poor performance and reported with an E code 

Atrazine, desethyl- 0.100 0.006 6 10

Azimphos-methyl .233 .024 10 23

Carbaryl .747 .039 5 75

Carbofuran .925 .031 3 93

Terbacil .833 .027 3 83

Pesticide deleted from method in November 1994 

Dimethoate 0.066 0.009 14 7

Surrogates 

HCH-d6, alpha- 0.771 0.025 3 77

Diazinon-d10 .809 .053 6 81

Terbuthylazine .739 .039 5 74

1Corrected for background concentrations of compound in surface water.
29

Table 7.--Reocvery and precision data from seven determinations

of the compounds at 0.1 microgram per liter in ground water

(Denver Federal Center Well 15)

[conc., concentration; μg/L, microgram per liter; E code, estimated value]

Compound

Mean

observed

 conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Alachlor 0.089 0.003 3 89

Atrazine .079 .002 3 79

Benfluralin .045 .005 10 45

Butylate .077 .003 3 77

Chlorpyrifos .074 .005 6 74

Cyanazine .079 .003 4 79

Dacthal .079 .003 4 79

DDE, p,p'- .051 .012 23 51

Diazinon .070 .002 3 70

Dieldrin .063 .008 13 63

Diethylanaline, 2,6- .065 .003 4 65

Disulfoton .132 .003 2 132

EPTC .077 .001 2 77

Ethalfluralin .043 .003 7 43

Ethoprop .073 .003 4 73

Fonofos .065 .002 3 65

HCH, alpha- .070 .002 2 70

HCH, gamma- .076 .003 4 76

Linuron .042 .006 14 42

Malathion .072 .004 5 72

Metolachlor .082 .004 4 82

Metribuzin .041 .003 6 41

Molinate .082 .003 4 82

Napropamide .080 .005 6 80

Parathion .054 .004 7 54

Parathion-methyl .047 .002 5 47

Pebulate .079 .003 3 79

Pendimethalin .046 .005 11 46

Permethrin, cis- .040 .009 23 40

Phorate .089 .003 4 89

Prometon .050 .002 4 50

Pronamide .098 .004 4 98

Propachlor .083 .004 4 83

Propanil .073 .003 4 73

Propargite .055 .006 11 55

Simazine .073 .003 4 73

Tebuthiuron .071 .002 3 71

Terbufos .094 .005 5 94

Thiobencarb .074 .003 4 74

Triallate .067 .003 4 67

Trifluralin .044 .004 9 44
30

Table 7.--Recovery and precision data from seven determinations

of the compounds at 0.1 microgram per liter in ground water

(Denver Federal Center Well 15)--Continued

Compound

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Pesticides having poor performance and reported with an E code

Atrazine, desethyl- 0.014 0.001 6 14

Azimphos-methyl .054 .005 9 54

Carbaryl .094 .007 8 94

Carbofuran .100 .005 5 100

Terbacil .110 .005 5 110

Pesticide deleted from method in November 1994 

Dimethoate 0.025 0.005 21 25

Surrogates 

HCH-d6, alpha- 0.824 0.030 4 82

Diazinon-d10 .998 .035 4 100

Terbuthylazine .853 .025 3 85

Table 8.--Recovery and precision data from six determinations

of the compounds at 1.0 microgram per liter in ground water

(Denver Federal Center Well 15)

[conc., concentration; μg/L, microgram per liter; E code, estimated value]

Compound

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Alachlor 0.893 0.034 4 89

Atrazine .766 .027 4 77

Benfluralin .568 .050 9 57

Butylate .699 .011 2 70

Chlorpyrifos .690 .054 8 69

Cyanazine .733 .045 6 73

Dacthal .809 .045 6 81

DDE, p,p'- .506 .035 7 51

Diazinon .742 .069 9 74

Dieldrin .624 .051 8 62

Diethylanaline, 2,6- .639 .017 3 64

Disulfoton .739 .037 5 74

EPTC .697 .016 2 70

Ethalfluralin .528 .038 7 53
31

Table 8.--Recovery and precision data from six determinations

of the compounds at 1.0 microgram per liter in ground water

(Denver Federal Center Well 15)--Continued

Compound

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Ethoprop 0.750 0.036 5 75

Fonofos .701 .032 5 70

HCH, alpha- .586 .021 4 59

HCH, gamma- .740 .041 6 74

Linuron .330 .164 50 33

Malathion .707 .027 4 71

Metolachlor .786 .030 4 79

Metribuzin .429 .020 5 43

Molinate .736 .007 1 74

Napropamide .732 .081 11 73

Parathion .572 .020 4 57

Parathion-methyl .530 .017 3 53

Pebulate .712 .011 2 71

Pendimethalin .550 .036 6 55

Permethrin, cis- .418 .043 10 42

Phorate .584 .016 3 58

Prometon .459 .022 5 46

Pronamide .996 .036 4 100

Propachlor .762 .007 1 76

Propanil .714 .033 5 71

Propargite .900 .124 14 90

Simazine .683 .023 3 68

Tebuthiuron .532 .052 10 53

Terbufos .605 .015 2 60

Thiobencarb .710 .035 5 71

Triallate .713 .039 5 71

Trifluralin .541 .034 6 54

Pesticides having poor performance and reported with an E code 

Atrazine, desethyl- 0.122 0.007 5 12

Azimphos-methyl .519 .041 8 52

Carbaryl .864 .073 8 86

Carbofuran .881 .046 5 88

Terbacil .763 .022 3 76

Pesticide deleted from method in November 1994 

Dimethoate 0.098 0.011 12 10

Surrogates 

HCH-d6, alpha- 0.885 0.050 6 89

Diazinon-d10 .934 .034 4 93

Terbuthylazine .874 .045 5 87
32

Table 9.--Method detection limit calculated from precision data for seven

determinations of the compounds in reagent water fortified

at initial detection limits estimated in table 3

[MDL, method detection limit; conc., concentration, μg/L, microgram per liter;

E code, estimated value]

Compound

MDL

expected

conc.

(μg/L)

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Method

detection

limit

(μg/L)

Alachlor 0.01 0.011 0.0005 4 113 0.002

Atrazine1 .01 .010 .0004 4 98 .001

Benfluralin .02 .010 .0005 5 51 .002

Butylate .01 .008 .0005 6 84 .002

Chlorpyrifos .01 .012 .0013 11 116 .004

Cyanazine .02 .014 .0013 9 71 .004

Dacthal .01 .016 .0005 3 156 .002

DDE, p,p'- .03 .034 .0019 6 113 .006

Diazinon .02 .017 .0007 4 84 .002

Dieldrin .03 .027 .0004 1 90 .001

Diethylanaline, 2,6- .01 .005 .0010 20 47 .003

Disulfoton .30 .247 .0053 2 82 .017

EPTC .01 .008 .0005 6 84 .002

Ethalfluralin .02 .020 .0013 6 102 .004

Ethoprop .02 .017 .0010 6 84 .003

Fonofos .02 .016 .0008 5 80 .003

HCH, alpha- .03 .029 .0005 2 95 .002

HCH, gamma- .03 .030 .0012 4 100 .004

Linuron .05 .011 .0007 6 22 .002

Malathion .03 .021 .0017 8 71 .005

Metolachlor .01 .011 .0006 5 110 .002

Metribuzin .04 .023 .0012 5 57 .004

Molinate .02 .018 .0012 6 90 .004

Napropamide .02 .025 .0010 4 124 .003

Parathion .03 .017 .0014 8 58 .004

Parathion-methyl .03 .014 .0018 13 46 .006

Pebulate .03 .023 .0013 5 78 .004

Pendimethalin .04 .017 .0014 8 42 .004

Permethrin, cis- .05 .025 .0016 6 50 .005

Phorate .02 .015 .0008 5 76 .002

Prometon .04 .018 .0058 32 45 .018

Pronamide .03 .021 .0010 4 71 .003

Propachlor .01 .010 .0021 21 100 .007

Propanil .02 .015 .0011 8 73 .004

Propargite .04 .026 .0040 16 64 .013

Simazine .03 .028 .0017 6 94 .005

Tebuthiuron .03 .032 .0030 10 106 .010

Terbufos .03 .042 .0040 10 139 .013

Thiobencarb .03 .027 .0008 3 91 .002

Triallate .01 .009 .0004 4 91 .001

Trifluralin .02 .012 .0008 6 59 .002
33

Table 9.--Method detection limit calculated from precision data for seven

determinations of the compounds in reagent water fortified

at initial detection limits estimated in table 3--Continued

Compound

MDL

expected

conc.

(μg/L)

Mean

observed

conc.

(μg/L)

Standard

deviation

(μg/L)

Relative

standard

deviation

(percent)

Mean

recovery

(percent)

Method

detection

limit

(μg/L)

Pesticides having poor performance and reported with an E code 

Atrazine, desethyl- 0.05 0.008 0.0007 8 16 0.002

Azimphos-methyl .03 .004 .0000 0 13 .001

Carbaryl .03 .007 .0011 15 24 .003

Carbofuran .02 .006 .0011 18 31 .003

Terbacil .03 .012 .0022 19 39 .007

Pesticide deleted from method in November 1994

Dimethoate 0.07 0.013 0.0014 11 19 0.004

1Six determinations were used for mean concentration and standard deviation after rejection

of one concentration (0.016 μg/L) as an outlier based on a Student's t-test (American Society for

Testing and Materials, 1993).

The preliminary estimated MDLs ranged from 0.004 to 0.039 μg/L

(table 3). According to the U.S. Environmental Protection Agency (1992)

procedure, the fortified concentrations should be no more than five times the

estimated MDL. Because the fortified concentration (0.1 μg/L) was more than

five times the estimated MDLs for many of the pesticides in table 3, another

MDL determination was conducted by fortifying seven replicates with the

compounds at the estimated MDLs determined in table 3. The MDLs

calculated from this procedure range from 0.001 to 0.018 μg/L (table 9). The

MDLs in table 9 are used as the default reporting value when no peak is

observed at the characteristic retention time.

The MDLs do not account for sample matrix. With clean environmental samples, it might be possible to detect compound concentrations less

than the MDL; conversely, in complex samples, it might not be possible to

detect compounds at concentrations greater than the MDL.

Recovery at different concentrations: For each sample matrix, samples

were grouped by concentration and compared using the nonparametric

Kruskal-Wallis test (reagent water) or Mann-Whitney test (ground water or

surface water) to examine the null hypothesis that the mean recoveries were

equal in each concentration (Miller and Miller, 1988). The F-test was used to

compare the variance of recovery in each concentration to examine the null

hypothesis that the precision was different in the two concentrations (Miller

and Miller, 1988).
34

In reagent-water samples, mean recoveries were comparable at 1.0 μg/L

(table 4), 0.1 μg/L (table 3), or 0.01 μg/L (table 9) for most compounds. For

some compounds (Malathion, Parathion-methyl and pronamide), the mean

recoveries were significantly lower (p <0.05; Mann-Whitney test) in the

0.1-μg/L sample set compared to the 1.0-μg/L set. For other compounds

(cyanazine, p,p'-DDE, dieldrin, 2,6-diethylaniline, metribuzin, molinate,

naproamide, prometon, propargite, and simazine), the mean 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 relatively small (4 to

15 percent) and might also be the result of variation in instrument

performance because each sample set was analyzed at different time periods.

Similarly, in the 0.01-μg/L sample set (table 9), mean recoveries of some

compounds (2,6-diethylaniline, chlorpyrifos, dacthal, EPTC, linuron,

molinate, propachlor, prometon, propargite, Terbufos) were significantly

greater (p <0.05; Kruskal-Wallis test) than in the 0.1- and 1.0-μg/L sample sets

(tables 3 and 4). However, this 0.01-μg/L sample set was prepared from a

different primary fortification solution than that for the 0.1- and 1.0-μg/L

samples, so these differences might be the result of differences in the solution

mixtures, as well as sample preparation and instrument calibration.

The average recovery and precision of all compounds in tables 3 and 4

were combined to calculate average recovery and precision in reagent water.

The average short-term, single-operator precision in reagent water at the 0.1-

and 1.0-μg/L level is 7 percent, and the average recovery is 73 percent. From

table 9, the average precision of all compounds in reagent water at 0.01 μg/L is

8 percent, and the average recovery is 83 percent.

In the Denver Federal Center Well 15 ground-water samples, mean

recoveries were comparable at 0.1-μg/L (table 7) and 1.0-μg/L (table 8)

concentration levels for most compounds. As in the case of reagent water,

mean recoveries of prometon and simazine were significantly higher

(p <0.05; Mann-Whitney test) in the 0.1-μg/L sample set compared to the

1.0-μg/L sample set. A few additional compounds (disulfoton, α-HCH,

phorate, tebuthiuron, Terbufos) had significantly higher recoveries (p <0.05;

Mann-Whitney test) in the 0.1-μg/L sample set compared to the 1.0-μg/L

sample set.

In surface-water samples from South Platte River, mean recoveries were

comparable at 0.1 μg/L (table 5) and 1.0 μg/L (table 6) concentration levels for

most compounds. As in the case of reagent-water and ground-water samples,

mean recovery of prometon was significantly higher (p < 0.05; MannWhitney test) in the 0.1-μg/L sample set compared to the 1.0-μg/L sample set.

Other compounds (alachlor, chlorpyrifos, disulfoton, α-HCH, ethoprop,

Linuron, Malathion, metribuzin, Parathion-methyl, phorate) had

significantly higher recoveries (p < 0.05; Mann-Whitney test) in the 0.1-μg/L

sample set compared to the 1.0-μg/L sample set. In addition, the relative
35

standard deviations of some compounds (ethoprop, pronamide, prometon,

chlorpyrifos, Diazinon) in the 0.1-μg/L sample set (table 5) were significantly

higher (p < 0.05; F-test for comparison of variance) (10 to 22 percent) than in

the reagent-water sample set (2 to 5 percent). Pronamide and Diazinon were

among those compounds corrected for background concentration in samples

from South Platte River.

Recovery in different matrices: The mean recovery of most compounds

was higher in the reagent-water sample sets (tables 3, 4, and 9) compared to

samples of surface water (tables 5 and 6) or ground water (tables 7 and 8).

Pronamide had significantly higher recoveries (p <0.05; Mann-Whitney test)

(98 and 100 percent) in the Denver Federal Center Well 15 ground-water

sample sets compared to reagent water (76 and 84 percent). In surface-water

samples from South Platte River, mean recoveries of ethoprop and the

dinitroaniline class of herbicides (benfluralin, ethafluralin, pendemethilin,

trifluralin) were significantly higher (p <0.05; Mann-Whitney test) (62 to 68

percent) than in reagent-water samples (46 to 54 percent).

Qualification or elimination of some compounds: A few compounds

produced poor performance in all matrices and all concentrations.

Dimethoate demonstrated small and variable recovery (7 to 25 percent) in all

sample-matrix types as a result of breakthrough on the SPE columns.

Breakthrough of Dimethoate in 10-L water samples using 10-g C-18 SPE

columns was observed by Foreman and Foster (1991). This compound has the

highest water solubility (20,000 mg/L) of the compounds tested, and

apparently is not well retained by the C-18 phase. Breakthrough is a function

of the volume of sample processed. Because the volume of sample processed

is variable, the precision of this compound tends to be unacceptably high and

variable. As a result of this poor performance, Dimethoate was deleted from

the method in November 1994.

Desethylatrazine also demonstrated small recovery (9 to 19 percent) in

all sample-matrix types because of poor retention on C-18 phase at 1-L sample

volumes. However, because of the national importance of this metabolite,

the compound was not deleted from the method, but the result is qualified by

reporting an "E" code.

Carbofuran, Carbaryl, terbacil, and azimphos-methyl demonstrated

variable performance because of problems in the GC/MS procedure, either as

a result of injector or coelution and integration problems. These compounds

are reported with an "E" code to qualify the result and caution the user that

concentrations are estimated and need to be evaluated carefully because of

variable performance. Carbofuran and Carbaryl, in particular, are subject to

variable performance because of contamination of injection liners. Early

method-performance evaluation (tables 3-8) was studied using Bond-Elut SPE

columns that resulted in a white precipitate after elution from the SPE
36

column which contaminated the injection liner. Changing to Isolute SPE

columns largely eliminated the precipitate and resulted in improved

performance of carbofuran and Carbaryl (compared to results listed in tables

3-8). Despite the improvement in performance with the Isolute columns,

these compounds are reported with an "E" code because of the potential for

variable performance.

Estimated holding time: The estimated holding time of samples after

extraction of the SPE column and storage at room temperature was estimated

using a mathematically defined procedure (ASTM Procedure D-4841-88)

(American Society for Testing and Materials, 1993). The maximum holding

time is defined as the 90-percent lower confidence limit of a specified critical

time. The critical time is defined as the time that a change in 10 percent of the

compound concentration from day zero occurred and when precision of the

method allowed that 10-percent change to be a statistically significant

difference at the 90-percent confidence level.

The relative standard deviation of analysis of samples fortified at

1.0 μg/L (table 4) was used to estimate the number of samples needed to

evaluate a significant change in concentration over time. The number of

replicates (table 10) was calculated according to the following equation:

n = 





 t x RSD

D

2

 (8)

where n = number of replicates;

t = Student's t-value, 3.707, based on seven replicates

used in table 4;

RSD = relative standard deviation (table 4); and

D = 15 percent, maximum variation from mean to be 

tolerated.

For most compounds, n was less than 3 (table 10), so this value was selected

for the holding-time study.

Reagent-water samples were fortified at 1.0 μg/L, extracted on day zero, and

stored at room temperature. Triplicate samples were eluted from the SPE

columns at discrete (3, 12, 14, and 28 days) time intervals over 28 days. All

samples were analyzed in one batch at the end of the experiment. Table 10

lists the tolerable variation d, calculated from the following formula:
37

Table 10.--Summary of statistical data used to determine estimated holding time

of compounds on solid-phase-extraction columns held at 25 degrees Celsius

[Reagent water samples were fortified at 1.0 μg/L, and triplicate samples were analyzed on days 3, 12, 14,

 and 28. n, number of replicates; d, determination; μg/L, micrograms per liter; conc., concentration; r2,

regression coefficient; --, estimated holding time could not be determined because compound did not

decrease in concentration over 28-day test period; E code, estimated value]

Compound

Calculated

holding

time

replicates

(n)

Tolerable

variation

(d) (99

percent)

(μg/L)

Extrapolated

day zero

conc.

(μg/L)

Slope

coefficient

Intercept

(d)

Regression

coefficient

(r2)

Estimated

holding

time

(days)

Alachlor 1 0.084 1.2 -0.00195 1.083 0.07 43

Atrazine 2 .098 1.1 -.00364 .984 .15 27

Benfluralin 3 .071 .6 .00197 .541 .22 --

Butylate 1 .075 .9 -.00035 .865 .006 213

Chlorpyrifos 3 .113 1.0 -.00321 .884 .12 35

Cyanazine 2 .102 1.0 -.00792 .936 .58 13

Dacthal 2 .099 1.2 -.0027 1.090 .08 37

DDE, p,p'- 11 .105 .4 .01294 .283 .51 --

Diazinon 2 .087 1.0 -.01229 .952 .68 7

Dieldrin 2 .065 .9 .00717 .856 .45 --

Diethylanaline, 2,6- 2 .082 .9 -.00692 .810 .43 12

Disulfoton 1 .074 1.1 -.00694 1.055 .60 11

EPTC 1 .076 1.0 -.00039 .907 .01 194

Ethalfluralin 3 .074 .7 .00102 .620 .02 --

Ethoprop 1 .059 1.2 -.00255 1.103 .13 23

Fonofos 1 .070 1.0 -.00284 .975 .17 25

HCH, alpha- 1 .065 1.1 -.00241 1.030 .09 27

HCH, gamma- 1 .068 1.1 -.00267 1.027 .13 25

Linuron 3 .194 .4 .00111 .253 .04 --

Malathion 1 .100 1.1 -.00024 .992 .001 418

Metolachlor 2 .095 1.1 -.00265 1.039 .14 36

Metribuzin 2 .039 .4 -.00199 .395 .17 20

Molinate 1 .058 1.0 -.00205 .930 .20 28

Napropamide 1 .058 1.0 .00574 .971 .37 --

Parathion 2 .119 1.0 -.00145 .876 .04 82

Parathion-methyl 2 .112 1.0 -.00259 .866 .18 43

Pebulate 1 .068 1.0 -.00095 .899 .05 71

Pendimethalin 3 .077 .7 .00697 .641 .49 --

Permethrin, cis- 21 .136 .2 .00749 .110 .39 --

Phorate 1 .059 1.1 -.00621 1.011 .48 10

Prometon 3 .099 .7 -.00327 .641 .17 30

Pronamide 1 .089 1.1 -.00661 1.016 .30 13

Propachlor 1 .059 1.0 -.00383 .959 .44 15

Propanil 2 .104 1.2 -.00232 1.087 .23 45

Propargite 6 .107 .6 -.00844 .524 .46 13

Simazine 2 .070 .7 -.00293 .710 .24 24

Tebuthiuron 2 .110 1.0 -.00363 .655 .24 109

Terbufos 1 .071 1.0 -.00576 .916 .60 12

Thiobencarb 2 .100 1.1 -.00177 1.011 .04 56
38

Table 10.--Summary of statistical data used to determine estimated holding time

of compounds on solid-phase-extraction columns held

at 25 degrees Celsius---Continued

Compound

Calculated

holding

time

replicates

(n)

Tolerable

variation

(d) (99

percent)

(μg/L)

Extrapolated

day zero

conc.

(μg/L)

Slope

coefficient

Intercept

(d)

Regression

coefficient

(r2)

Estimated

holding

time

(days)

Triallate 2 0.081 1.0 -0.0022 0.923 0.11 37

Trifluralin 3 .071 .6 -.00137 .568 .15 9

Pesticides having poor performance and reported with an E code 

Atrazine, desethyl- 2 0.012 0.1 -0.00006 0.093 0.002 204

Azimphos-methyl 2 .108 .7 -.00548 .600 .36 20

Carbaryl 6 .437 .7 -.00983 .219 .32 44

Carbofuran 2 .141 .6 -.00856 .469 .38 16

Terbacil 2 .069 .6 -.00798 .511 .64 9

Pesticide deleted from method in November 1994 

Dimethoate 7 0.011 0.1 -0.00121 0.080 0.57 9

Surrogates

HCH-d6, alpha- 1 0.090 1.1 -0.00132 0.965 0.03 68

Diazinon-d10 2 .124 1.0 -.01247 .873 .76 10

Terbuthylazine 2 .128 1.1 -.00239 .993 .07 54

d = ± t • s (9)

 n

where d = range of tolerable variation from initial concentration;

t = Student's t-value, 3.707, based on seven replicates used in 

precision study;

s = standard deviation (table 4); and

n = 3, number of replicates.

Linear curves were fit to the data and the day-zero intercept was

calculated from the regression line. The estimated d value, in micrograms

per liter, then was subtracted from the day-zero value to give the lower

tolerable range of variation from the day-zero concentration. The intercept of

the linear fit of the concentration in relation to the time line with the lower

tolerable range concentration gives the estimated holding time. Diazinon,

terbacil, Dimethoate, phorate, Diazinon-d10, and trifluralin had estimated
39

holding times of 10 days or less (table 10). The shortest is Diazinon at 7 days,

which is the maximum allowable holding time of the SPE columns after

extraction for the method.

Automation--The method is ideally suited for automation 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 set-up 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 of exceeding the

estimated pre-extraction holding-time limit of 4 days and avoids complications and expense of overnight shipping of samples to the laboratory.

CONCLUSIONS

From the data presented in this report, SPE and determination by

GC/MS is shown to be a sensitive and reliable method for the determination

of low concentrations of a broad range of pesticides in water samples. This

report presents a method for routine analysis of 41 pesticides and metabolites

in natural-water samples. Method detection limits range from 0.001 to 0.018

μg/L. Average short-term single-operator precision in reagent-water samples

is 7 percent at the 0.1- and 1.0-μg/L levels and 8 percent at the 0.01-μg/L level.

Mean recoveries in reagent-water samples are 73 percent at the 0.1- and

1.0-μg/L levels and 83 percent at the 0.01-μg/L level.

Because of GC or SPE problems, five compounds (desethylatrazine,

azimphos-methyl, Carbaryl, carbofuran, and terbacil) demonstrated variable

performance and are reported as estimated values. One compound,

Dimethoate, was deleted from the method because of variable recovery

by SPE.
40

REFERENCES CITED

American Society for Testing and Materials, 1992, Annual book of ASTM

standards, Section 11, Water: Philadelphia, American Society for

Testing and Materials, v. 11.01, p. 8-13.

_____1993, Annual book of ASTM standards, Section 11, Water:

Philadelphia, American Society for Testing and Materials, v. 11.01,

p. 31-44.

Bagnati, R., Benfenati, E., Davoli, E., and Fanelli, R., 1988, Screening of 21

pesticides in water by a single extraction with C-18 silica bonded phase

columns and HRGC-MS: Chemosphere, v. 17, no. 1, p. 59-65.

Battista, Massimo, DiCorcia, Antonio, and Marchetti, Marcello, 1989,

Extraction and isolation of triazine herbicides from water and

vegetables by a double trap tandem system: Analytical Chemistry,

v. 61, no. 9, p. 935-939.

Bellar, T.A., and Budde, W.L., 1988, Determination of nonvolatile organic

compounds in aqueous environmental samples using liquid

chromatography/mass spectrometry: Analytical Chemistry, v. 60,

no. 19, p. 2076-2083.

Brooks, M.W., Jenkins, Jeffrey, Jimenez, Miguel, Quinn, Theresa, and Clark,

J.M., 1989, Rapid method for the determination of alachlor, atrazine

and metolachlor in groundwater by solid-phase extraction: Analyst, v.

114, p. 405-406.

DiCorcia, Antonio, Marchetti, Marcello, and Samperi, Roberto, 1989,

Extraction and isolation of phenoxy acid herbicides in environmental

waters using two adsorbants in one minicartridge: Analytical

Chemistry, v. 61, no. 13, p. 1363-1367.

Edwards, T.K., and Glysson, G.D., 1988, Field methods for measurement of

fluvial sediment: U.S. Geological Survey Open-File Report 86-531,

118 p.

Eichelberger, J.W., Behymer, T.D., and Budde, W.L., 1988, Method 525--

Determination of organic compounds in drinking water by liquidsolid extraction and capillary GC/MS, in Methods for the

determination of organic compounds in drinking water: Cincinnati,

U.S. Environmental Protection Agency, Environmental Monitoring

and Support Laboratory, p. 325-356.
41

Fishman, M.J., 1993, Methods of analysis by the U.S. Geological Survey

National Water Quality Laboratory--Determination of inorganic and

organic constituents in water and fluvial sediments: U.S. Geological

Survey Open-File Report 93-125, 217 p.

Foreman, W.T., and Foster, G.D., 1991, Isolation of multiple classes of

pesticides from large-volume water samples using solid phase

extraction cartridges, in Mallard, G.E., and Aronson, D.A., eds., U.S.

Geological Survey toxic substances hydrology program--Proceedings of

the technical meeting, Monterey, California, March 11-15, 1991: U.S.

Geological Survey Water-Resources Investigations Report 91-4034,

p. 530-533.

Gianessi, L.P., Peskin, H.M., and Puffer, C.A., 1986, A national data base of

nonurban nonpoint source discharges and their effect on the Nation's

water quality: Report prepared for the U.S. Environmental Protection

Agency, Office of Standards and Regulations under Cooperative

Agreement CR 811858-01-0, 14 p.

Gianessi, L.P., and Puffer, C.A., 1990 (revised 1991), Herbicide use in the

United States: Washington, D.C., Resources for the Future, December

1990 (Revised April 1991), 128 p.

Gianessi, L.P., and Puffer, C.A., 1992a, Fungicide use in U.S. crop production:

Washington, D.C., Resources for the Future, November 1992.

Gianessi, L.P., and Puffer, C.A., 1992b, Insecticide use in U.S. crop production:

Washington, D.C., Resources for the Future, August 1992.

Hallberg, G.R., 1989, Pesticide pollution of groundwater in the humid United

States: Agriculture, Ecosystems and Environment, v. 26, p. 299-367.

Hardy, M.A., Leahy, P.P., and Alley, W.M., 1989, Well installation and

documentation and ground-water sampling protocols for the pilot

National Water-Quality Assessment program: U.S. Geological Survey

Open-File Report 89-396, 36 p.

Junk, G.A., and Richard, J.J., 1988, Organics in water--Solid-phase extraction

on a small scale: Analytical Chemistry, v. 60, no. 5, p. 451-454.

Leistra, M., and Boesten, J.J.T.I., 1989, Pesticide contamination of groundwater

in Western Europe: Agriculture, Ecosystems and Environment, v. 26,

p. 369-389.

Miller, J.C., and Miller, J.N., 1988, Statistics for analytical chemistry (2d ed.):

New York, Ellis Horwood Limited, 227 p.
42

Sandstrom, M.W., 1989, Field method for isolation of herbicides in surface

and ground water using solid-phase extraction, in Pederson, G.L., and

Smith, M.M., eds., U.S. Geological Survey second national symposium

on water quality--Abstracts of the technical sessions, Orlando, Florida,

November 12-17, 1989: U.S. Geological Survey Open-File Report

89-409, p. 82.

Sandstrom, M.W., in press, Filtration of water-sediment samples for

determination of organic compounds: U.S. Geological Survey WaterResources Investigations Report 95-4105.

Sandstrom, M.W., Wydoski, D.S., Schroeder, M.P., Zamboni, J.L., and

Foreman, W.T., 1992, Methods of analysis by the U.S. Geological

Survey National Water Quality Laboratory--Determination of

organonitrogen herbicides in water by solid-phase extraction and

capillary-column gas chromatography/mass spectrometry with

selected-ion monitoring: U.S. Geological Survey Open-File

Report 91-519, 26 p.

Thurman, E.M., Meyer, M.M., Pomes, M., Perry, C.E., and Schwab, A.P., 1990,

Enzyme-linked immunosorbent assay compared with GC/MS for the

determination of herbicides in water: Analytical Chemistry,

v. 62, no. 18, p. 2043-2048.

Timme, P.J., 1994, National Water Quality Laboratory 1994 services catalog:

U.S. Geological Survey Open-File Report 94-304, 103 p.

Ward, J.R., and Harr, C.A., eds., 1990, Methods for collection and processing of

surface-water and bed-material samples for physical and chemical

analyses: U.S. Geological Survey Open-File Report 90-140, 71 p.

Wershaw, R.L., Fishman, M.J., Grabbe, R.R., and Lowe, L.E., eds., 1987,

Methods for the determination of organic substances in water and

fluvial sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A3, 80 p.

U.S. Environmental Protection Agency, 1992, 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, revised as of July 1, 1992,

p. 565-567.
43

Supplement A--Automated Solid-Phase Extraction

Procedure Using AutoTrace Workstation
44

Zymark AutoTrace Extraction Workstation 1.20

[mL, milliliter]

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 into SOLVENT WASTE

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

Step 9 : Clean each sample path with 100 mL 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
45

Supplement B--On-site Solid-Phase Extraction Procedure
46

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

Schedule 2010

Instructions for On-Site Processing Using Solid-Phase Extraction

(SPE)

1. Gather the equipment and supplies needed for on-site SPE listed in

table 11.

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 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 using

the cleaning solutions and graduated cylinder or beaker to measure volume.
47

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 rinsed 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 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).

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 or

distilled 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 DENSUPL section) 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 (EDOC - FWWIEBE; 303-467-8178), Mark

Sandstrom (EDOC - SANDSTRO; 303-467-8086), or Steve Zaugg (EDOC -

SDZAUGG; 303-467-8207) for additional information.
48

Table 11.--Equipment and supplies required for broad spectrum pesticide

analysis (Schedule 2010) by onsite 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]

Item

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 1

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

Supplies

SPE columns, Analytichem 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 vial1 1

Liquinox detergent, 0.2-percent solution, 4-L 1

B&J methanol, 4-L 1

B&J water, 4-L 1

Aluminum foil, roll 1

Gloves, disposable, nonpowdered, medium 1-5

Spike kit, including Instruction Manual1 1

Spike mixture, 1-10 ng/μL, 2-mL vial1 1

1Supplies obtained through NWQL DENSUPPL.
National Water Quality Laboratory 49 USGS-WRD

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

Schedule 2010

Station ID or Unique Number: _______________ Station Name 

Date: Time Collector: 

Telephone Number of Collector: 

Comments:

NWQL INFORMATION

 SPE Cartridge Type:

Lot #:

Dry Wt.: g

FIELD INFORMATION

 Filter Sample 0.7-μm glass fiber filter Date filtered: 

 SPE Cartridge Conditioning: Date of SPE procedure: 

Methanol (2 mL): mL

Organic-free water (2 mL): mL

(DO NOT LET CARTRIDGE GO DRY ONCE CONDITIONING STARTED)

 Sample Sample + bottle: g

(-) bottle tare wt.: g

= Sample wt.: g

Add 1% methanol: mL

Sample + bottle + MeOH: g

 Surrogate Solution ID:

Volume added: μL

 QA Samples - Spike Mixture

Solution ID:

Volume added: μL

 Sample through cartridge

Sample + plastic beaker: g

plastic beaker: g

 Flow rate: Start time: hr:min

Finish time: hr:min

 Remove excess water - Write station ID, date, time on cartridge - Store in 40-mL vial @ 4°C

NWQL INFORMATION

Lab ID: Set #: Date Received

 Dry cartridge with CO2: Date: 

Pressure: lb/in2

Time: min

SPE cartridge wt.: g

 SPE Elution Date: 

add 1.8 mL HIP (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: