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

Seal
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

By Mark W. Sandstrom, Duane S. Wydoski, Michael P. Schroeder,

Jana L. Zamboni, and William T. Foreman

U.S. GEOLOGICAL SURVEY

Open-File Report 91-519

Seal

Denver, Colorado

First Printing, 1992

Second printing with minor revisions, 1994
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U. S. GEOLOGICAL SURVEY

Robert M. Hirsch, Acting Director

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 Books and Open-File Reports Section

5293 Ward Road, Mail Stop 407 Box 25425, Mail Stop 517

Arvada, CO 80002 Federal Center

Denver, CO 80225
i
ii
iii

CONTENTS

 Page 

Abstract....................................................................................................................... 1

Introduction .............................................................................................................. 1

Analytical method ................................................................................................... 2

1. Scope and application................................................................................ 2

2. Summary of method................................................................................. 3

3. Interferences................................................................................................ 3

4. Apparatus and equipment ....................................................................... 4

5. Reagents and consumable materials...................................................... 6

6. Sampling methods, sample-collection equipment, and

cleaning procedures............................................................................ 7

6.1 Sampling methods....................................................................... 7

6.2 Sample-collection equipment................................................... 7

6.3 Cleaning procedures.................................................................... 8

7. Gas chromatograph/mass spectrometer performance....................... 8

7.1 Gas chromatograph performance evaluation........................ 8

7.2 Mass spectrometer performance evaluation.......................... 8

8. Calibration ................................................................................................... 8

9. Procedure ..................................................................................................... 11

10. Calculation and reporting of results...................................................... 14

10.1 Sample analysis and data evaluation...................................... 14

10.2 Qualitative identification........................................................... 15

10.3 Quantitation.................................................................................. 16

10.4 Reporting concentrations........................................................... 17

Method performance............................................................................................... 17

Conclusions............................................................................................................... 24

References cited ........................................................................................................ 25

FIGURES

Figures 1-3. Sketches showing:

1. Solid-phase-extraction vacuum manifold................................... 12

2. Solid-phase-extraction pumping apparatus ................................ 13

3. Apparatus used for elution of analytes from solid-phaseextraction cartridges by gravity flow....................................... 15
iv

TABLES

 Page 

Table 1. Constituent codes, laboratory codes, and Chemical Abstracts

Service registry numbers for method analytes.......................... 4

2. Retention time, relative retention time, quantitation ion,

and confirmation ions for target compounds, surrogate

compound, and internal standard ............................................... 10

3. Accuracy and precision data from seven determinations of

the method analytes at 0.2 microgram per liter in reagent

water.................................................................................................... 18

4. Accuracy and precision data from seven determinations

of the method analytes at 2.0 micrograms per liter

in reagent water................................................................................ 19

5. Accuracy and precision data from seven determinations of

the method analytes at 0.2 microgram per liter in surface

water (South Platte River)............................................................. 20

6. Accuracy and precision data from seven determinations of

the method analytes at 2.0 micrograms per liter in

surface water (South Platte River)................................................ 21

7. Accuracy and precision data from seven determinations of

the method analytes at 0.2 microgram per liter in ground

water (Arvada Well No. 14)........................................................... 22

8. Accuracy and precision data from seven determinations of

the method analytes at 2.0 micrograms per liter in

ground water (Arvada Well No. 14)............................................ 23
v

CONVERSION FACTORS AND

ABBREVIATED WATER-QUALITY UNITS

 Multiply By To obtain 

centimeter (cm) 3.94 X 10-1 inch

inch (in.) 25.4 millimeter

gram (g) 3.53 X 10-2 ounce

kilopascal (kPa) 0.296 inch of mercury (Hg)

liter (L) 0.265 gallon

meter (m) 3.28 foot

microgram (μg) 3.53 X 10-8 ounce

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 terms and abbreviations also are used in this report:

oC/min degrees Celsius per minute

GC/MS gas chromatograph/mass spectrometer

ID inside diameter

MDL method detection limit

μg/L microgram per liter

ng/μL nanogram per microliter

OD outside diameter

PAH polyaromatic hydrocarbon

PFTBA perfluorotributylamine

RT retention time

SIM selected-ion monitoring

SPE solid-phase extraction

Teflon-PFA Teflon-perfluoroalkoxy

Tefzel-ETFE Tefzel-ethylenetetrafluoroethylene
1

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

By MARK W. SANDSTROM, DUANE S. WYDOSKI, MICHAEL P. SCHROEDER,

JANA L. ZAMBONI, and WILLIAM T. FOREMAN

ABSTRACT

A method for the isolation of organonitrogen herbicides from natural

water samples using solid-phase extraction and analysis by capillary-column

gas chromatography/mass spectrometry with selected-ion monitoring is

described. Water samples are filtered to remove suspended particulate matter

and then are pumped through disposable solid-phase extraction cartridges

containing octadecyl-bonded porous silica to remove the herbicides. The

cartridges are dried using carbon dioxide, and adsorbed herbicides are

removed from the cartridges by elution with 1.8 milliliters of hexaneisopropanol (3:1). Extracts of the eluants are analyzed by capillary-column gas

chromatography/mass spectrometry with selected-ion monitoring of at least

three characteristic ions. The method detection limits are dependent on

sample matrix and each particular herbicide. The method detection limits,

based on a 100-milliliter sample size, range from 0.02 to 0.25 microgram per

liter. Recoveries averaged 80 to 115 percent for the 23 herbicides and 2

metabolites in 1 reagent-water and 2 natural-water samples fortified at levels

of 0.2 and 2.0 micrograms per liter.

INTRODUCTION

Organonitrogen herbicides include some of the most widely used

agricultural pesticides (Gianessi and others, 1986). They also are the most

frequently detected pesticides in ground water in the United States (Hallberg,

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

determining residues of these herbicides in natural-water samples involves
2

liquid-liquid extraction with an organic solvent followed by analysis by gas

chromatography with nitrogen-phosphorus detection, using two columns for

confirmation of herbicide identity.

Recently, methods for herbicide 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 lesser laboratory expenses.

The SPE methods can be conducted at the field site, which enables processing

of samples with labile analytes or processing samples 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 full scan and in a selected-ion monitoring (SIM)

mode for confirmation and quantitation of herbicides. The GC/MS is a more

sensitive and more specific detector than is the nitrogen-phosphorus detector.

This report describes a method for determining organonitrogen

herbicides developed by the U.S. Geological Survey for use in the Survey's

National Water Quality Laboratory. The method incorporates SPE for

removal of the herbicides from water samples and a GC/MS operated in the

SIM mode for selective confirmation and quantitation of the herbicides. The

method supplements other methods of the U.S. Geological Survey for

determination of organic substances in water that are described by Wershaw

and others (1987). The method was implemented in the National Water

Quality Laboratory in March 1991.

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

from sampling protocol through calculation and reporting of results.

Precision and accuracy data, and method detection limits for 23 organonitrogen herbicides and 2 metabolites of atrazine--desethylatrazine and

desisopropylatrazine--are presented.

ANALYTICAL METHOD

Parameters: Organonitrogen herbicides, dissolved, O-1121-91

(See table 1 for codes.)

1. Scope and application

This method is suitable for the determination of selected organonitrogen

herbicides and metabolites in natural-water samples containing at least

0.05 μg/L of each herbicide or metabolite. The method is applicable to

herbicides and metabolites that are: (1) Efficiently partitioned from the water
3

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

herbicides and metabolites. The method was used to determine the

concentrations of the 23 herbicides and the 2 metabolites of atrazine--

desethylatrazine and desisopropylatrazine--listed in table 1. The 23 herbicides

are those in the current (1991) National Water Quality Laboratory schedule

1389, which includes herbicides added to the schedule as part of the U.S.

Geological Survey's National Water Quality Assessment Program.

Previously completed development of the method (Sandstrom, 1989), as

well as other comparable methods (Thurman and others, 1990) served as

background for this report. Testing of the method included adjustment of

sample volume and final extract volume to optimize recovery of the

herbicides, especially the metabolites of atrazine--desethylatrazine and

desisopropylatrazine.

2. Summary of method

2.1 Water samples (100 mL) are filtered to remove suspended

particulate matter. Glass-fiber filters with a nominal 0.7-μm pore diameter or

disposable, in-line filter units, containing a nylon membrane with a nominal

0.45-μm pore diameter depending on the concentration of the suspended

particulate matter in the water samples, are used.

2.2 Filtered water samples are pumped through disposable,

polypropylene SPE cartridges containing 0.5 g of porous silica coated with a

C-18 organic phase that is chemically bonded to the surface of the silica.

2.3 The SPE cartridges are dried using a gentle stream of carbon dioxide

to remove interstitial water.

2.4 The adsorbed herbicides and metabolites are removed from the SPE

cartridges by elution with 1.8 mL of hexane-isopropanol (3:1).

2.5 The eluant is further evaporated using a gentle stream of nitrogen

to a final volume of 100 μL.

2.6 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 herbicides and

metabolites of interest may interfere.
4

Table 1.--Constituent codes, laboratory codes, and Chemical Abstracts

Service registry numbers for method analytes

[CAS, Chemical Abstracts Service; --, no code assigned]

Herbicide or

metabolite

Constituent code Laboratory

code

CAS number

Alachlor 46342 1587 15972-60-8

Ametryn 38401 1588 834-12-8

Atrazine 39632 1589 1912-24-9

Bromacil -- -- 314-40-9

Butachlor -- -- 23184-66-9

Butylate -- -- 2008-41-5

Carboxin -- -- 5234-68-4

Cyanazine -- 1590 21725-46-2

Cycloate -- -- 1134-23-2

Desethylatrazine -- 1591 6190-65-4

Desisopropylatrazine -- 1592 1007-28-9

Diphenamid -- -- 957-51-7

Hexazinone -- -- 51235-04-2

Metolachlor 39415 1593 51218-45-2

Metribuzin 82360 1594 21087-64-9

Prometon -- 1597 1610-18-0

Prometryn -- 1598 7287-19-6

Propachlor -- -- 1918-16-7

Propazine 38535 1595 139-40-2

Simazine -- 1596 122-34-9

Simetryn -- -- 1014-70-6

Terbacil -- -- 5902-51-2

Terbuthylazine -- -- 5915-41-3

Trifluralin -- -- 1582-09-8

Vernolate -- -- 1929-77-7

4. Apparatus and equipment

4.1 The apparatus and equipment required for this method are listed as

follows; specific sources and models used during the development of this

method also are listed, where applicable:

4.1.1 Sample containers--125-mL, amber glass bottles fitted with

Teflon-lined1 screw caps.

 1 The use of trade and brand names in this report is for identification

purposes only, and does not constitute endorsement by the U.S. Geological
5

4.1.2 Pipetting needles--Stainless steel, 16 gage [1.65 mm outside

diameter (OD)], blunt tip with Luer-Lok fitting, 2.54-cm long; Popper and

Sons, Inc.

4.1.3 Cleaning/elution module for SPE cartridges; Supelco, Inc.,

Visiprep Solid Phase Extraction Vacuum Manifold and Visidry Drying

Attachment or equivalent.

4.1.4 Ceramic-piston, valveless metering pump with fittings for

1/8-in. OD tubing; Fluid Metering Inc., Model QSY-2 CKC or equivalent.

4.1.5 Teflon-perfluoroalkoxy (Teflon-PFA) tubing, 1/8-in OD; ColeParmer Instrument Co., CL-06375-01 or equivalent.

4.1.6 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 1/8-in. OD tubing connector;

Upchurch Scientific.

4.1.7 Bottle-top solvent dispenser, 1 to 5 mL; Brinkmann

Dispensette.

4.1.8 Vacuum pump--Any vacuum pump with sufficient capacity

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

4.1.9 Micropipettes--50- and 100-μL, fixed- and variable-volume

micropipettes with disposable glass capillaries; VWR Scientific.

4.1.10 Analytical balance--Any analytical balance capable of

accurately weighing 150 g ± 0.1 g.

4.1.11 Fused-silica capillary column--Any fused-silica capillary

column that provides adequate resolution, capacity, accuracy, and precision.

A 25-m x 0.25-mm inside diameter (ID) fused-silica capillary column coated

with a 0.25-μm bonded film of polyphenylmethylsilicone was used; J&W, DB5 or equivalent.

4.1.12 Evaporative concentrator; Pierce Reacti-Vap evaporator and

Reacti-Therm heating module or equivalent. The heat-block temperature

needs to be maintained at 25°C.

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

equivalent.

 

Survey.
6

4.1.13.1 GC conditions: oven, 100°C (hold 5 minutes), and

then program to 240°C at 6°C/min, then hold for 7 minutes; injection port,

240°C; carrier gas, helium; injection volume, 2 μL, splitless injection.

4.1.13.2 MS conditions: interface, 235°C; dwell time 20

milliseconds; mass ions monitored are listed in table 2 (in section 8 later in

the report).

5. Reagents and consumable materials

5.1 Helium carrier gas, as contaminant free as possible (Grade 5).

5.2 Carbon dioxide gas for drying, high purity.

5.3 Nitrogen gas for evaporation, high purity.

5.4 SPE cartridges; Analytichem International, Bond-Elut No. 607313 or

equivalent. The disposable cartridges are packed with 500 mg of silica coated

with a chemically bonded C-18 hydrocarbon phase. The solid packing

material is held in place with stainless-steel frits.

5.5 Disposable filter units; Rainin Instrument Co., Inc., Nylon-66

disposable syringe filter units or equivalent. Filters consist of a 25-mm

diameter nylon membrane, nominal 0.45-μm pore diameter, enclosed in a

nylon housing with Luer-Lok inlet and outlet fittings.

5.6 Glass-fiber filters (142-, 47-, or 25-mm diam.), nominal 0.7-μm pore

diameter (GF/F grade); Whatman, Inc.

5.7 Stainless-steel filtration units (142-, 47-, or 25-mm diam.); Baxter

Scientific Products.

5.8 Solvents: Hexane, isopropanol, methanol, and reagent water; B&J

Brand, high-purity pesticide quality or equivalent.

5.9 Disposable glass capillaries, to fit the 50- and 100-μL, fixed- and

variable-volume micropipettes; VWR Scientific. The glass capillaries are

precleaned by baking at about 350oC for 2 hours.

5.10 Stock standard solutions. Obtain the herbicides, metabolites, and

internal standard either as pure materials from the U.S. Environmental

Protection Agency's Pesticide and Industrial Chemicals Repository or as

certified solutions from commercial vendors. If pure materials are obtained,

prepare standard solutions by diluting 5 to 10 mg of the pure material with

toluene in a 5- or 10-mL volumetric flask.

5.11 Primary fortification and dilution standard solutions. Use the

individual stock standard solutions to prepare low-concentration (5 ng/μL)
7

and high-concentration (12.5 ng/μL) primary fortification and dilution

standard solutions. Prepare these solutions by combining appropriate

volumes of the stock standard solutions in a 2- or 5-mL volumetric flask and

diluting with methanol. Add a 100-μL aliquot of the low-concentration or

high-concentration solution to a 2-L water sample to obtain concentrations of

0.25 or 1.25 ng/μL for the method performance-evaluation studies. Use part

of the high-concentration solution to prepare the calibration solutions.

5.12 Fortification solution of the polyaromatic hydrocarbon (PAH)

internal standard. Prepare a solution of phenanthrene-d10 in toluene at a

concentration of 50 ng/μL by diluting the stock standard solutions. Use part

of this solution to prepare the calibration solutions. Dilute part of this

solution to 5.0 ng/μL (add 200-μL to a 2-mL volumetric flask containing

water) and use for adding to the sample eluants after nitrogen evaporation of

the eluants to about 100 μL.

5.13 Surrogate standard solution. Prepare a solution of terbuthylazine in

methanol at a concentration between 1.0 to 2.0 ng/μL. Add this solution to

each sample prior to extraction by the SPE method (a 50-μL aliquot of this

solution added to 100 mL of the sample should result in a concentration of

between 0.5 to 1.0 μg/L of the surrogate).

5.14 Calibration solutions. Prepare a series of six calibration solutions in

hexane-isopropanol (3:1) that contain all herbicides and metabolites at

concentrations from 0.05 to 10.0 ng/μL and the PAH internal standard at a

constant concentration of 0.25 ng/μL. Prepare these calibration solutions by

appropriate dilutions of the high-concentration (12 ng/μL) primary

fortification and dilution standard solution.

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 (in press). 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 plastic tubing, gaskets, and

other parts that might leach interferences into water samples or sorb the

herbicides and metabolites from the water. Use refrigerated, glass sample

containers in automatic samplers that composite samples over time.
8

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 high purity methanol (contained in a

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

sample is collected to prevent contamination of the samples.

7. Gas chromatograph/mass spectrometer performance

7.1 Gas chromatograph performance evaluation

The gas chromatograph performance normally is indicated by peak

shape and by the variation of the target-compound (herbicide or metabolite)

response factors relative to response factors obtained using a new capillary

column and freshly prepared calibration solutions. 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.

7.2 Mass spectrometer performance evaluation

7.2.1 Check the mass spectrometer prior to the analysis of any

samples and every 24 hours thereafter during a series of analyses to ensure

mass spectrometer performance according to the perfluorotributylamine

(PFTBA) criteria outlined below. In addition, initially adjust the mass

spectrometer to ensure that the established reporting level for each target

compound can be achieved.

7.2.2 Tune the mass spectrometer daily using the procedure and

standard software supplied by the manufacturer. Parameters in the tuning

software initially optimize the resolution at masses 69, 131, 264, and 502 in the

spectrum of PFTBA. Manually adjust the resolution so that the 131 and 219

ions are 100 ± 20 percent, and the 414 ion is 10 ± 5 percent relative to the

abundance of the 131 and 219 ions.

8. Calibration

8.1 Initial calibration data are acquired by using a new capillary column

and freshly prepared calibration solutions. These data are used in subsequent

evaluation of the GC/MS performance.

8.2 Prior to the analysis of each sample set and every 24 hours

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

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

the GC/MS performance is in compliance with the established criteria.
9

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

solution into the GC/MS according to the GC/MS conditions described in

paragraph 7.2. Calculate the relative retention time for each target compound

and the surrogate compound (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

target compound or surrogate compound; and

RTi = uncorrected retention time of the quantitation ion of the

internal standard (phenanthrene-d10).

8.4 Calculate a response factor (RFc) for each target compound and the

surrogate compound 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 target

compound or surrogate compound;

Ci = concentration of the internal standard, in nanograms per

microliter;

Cc = concentration of the target compound or surrogate

compound, in nanograms per microliter; and

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

standard.

8.5 See table 2 for the respective quantitation ions and internalstandard reference used in these calculations. Use of the quantitation ions

and internal standard specified is mandatory.

8.6 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
10

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

confirmation ions for target compounds, surrogate compound,

and internal standard

[S, surrogate compound; IS, internal standard;

m/z, mass per unit charge; --, not used]

Com- Retention Relative Quanti- Second Third

Compound pound

type or

number

time

(minutes)

retention

time1

tation

ion

(m/z)

confirmation ion

(m/z)

confirmation ion

(m/z)

Butylate 1 15.328 0.671 174 217 146

Vernolate 2 15.709 .687 128 86 43

Propachlor 3 19.437 .850 120 176 93

Cycloate 4 19.888 .870 154 -- --

Desisopropylatrazine 5 20.106 .880 158 160 91

Desethylatrazine 6 20.388 .892 172 187 58

Trifluralin 7 20.724 .907 306 264 335

Simazine 8 21.944 .960 201 186 173

Prometon 9 21.970 .961 210 225 168

Atrazine 10 22.149 .969 200 215 173

Propazine 11 22.312 .976 214 229 172

Terbuthylazine S 22.487 .984 214 229 173

Phenanthrene-d10 IS 22.86 1.000 188 -- --

Terbacil 14 23.395 1.023 161 160 116

Metribuzin 15 24.608 1.076 198 199 144

Simetryn 16 24.973 1.092 213 198 170

Ametryn 17 25.139 1.100 227 212 185

Alachlor 18 25.154 1.100 160 188 237

Prometryn 19 25.260 1.105 241 184 199

Bromacil 20 25.891 1.133 205 207 188

Metolachlor 21 26.453 1.157 162 238 146

Cyanazine 22 26.534 1.161 225 198 173

Diphenamid 23 27.222 1.191 167 72 239

Butachlor 24 29.045 1.271 176 160 188

Carboxin 25 30.2 1.321 143 235 87

Hexazinone 26 34.248 1.498 171 252 128

1Relative to phenanthrene-d10 internal standard.
11

working concentration range for each target compound or surrogate

compound. Use the average response factors for the calibration-solution

range in subsequent sample target-compound quantitation.

8.7 Subsequent daily response factors calculated for each compound

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

compound of interest. Analyze at least one calibration solution daily.

8.8 The latest response factors calculated can be added to prior response

factors and a new average response factor calculated, 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.

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

calculation of the calibration-standard concentration agrees within ± 20

percent of the expected value.

9. Procedure

9.1 Set up the solid-phase-extraction vacuum manifold as shown in

figure 1. Attach the SPE cartridges to the Luer-Lok fittings and twist

counterclockwise to open the fittings. Preclean the SPE cartridges by rinsing

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

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

cartridge by either nitrogen positive pressure or vacuum. The clean cartridges

can be stored in 40-mL glass vials until used.

9.2 Set up the solid-phase-extraction pumping apparatus as shown in

figure 2. Rinse the Teflon-PFA tubing, pump, and in-line filter (if used) with

methanol:water (1:1). 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 cartridge. Ensure there are no leaks in any of the fittings and

that the sample bottle is vented to prevent negative pressures and bubbles

from forming during sample pumping. If an in-line filter is used, flush all air

from the lines before attaching the filter, otherwise air pockets will prevent

flow through the filter, and the connections will leak.

9.3 Immediately before sample extraction, condition a SPE cartridge

with 3 mL of methanol followed by 3 mL of reagent water by allowing the

solvents to drain through the cartridge by gravity. About 10 minutes is

required to allow the methanol and water to drip through the cartridge.

Important: The SPE cartridge bed needs to be completely covered with

methanol or water at all times once conditioning (or sampling) has begun.
12

VACUUM

MANIFOLD

GAS-PRESSURE

MODULE

SPE CARTRIDGES

VACUUM

GAGE

VACUUM

BLEED-VALVE

DRYING-GAS LINE

DRYING-GAS

ON-OFF

VALVES

UNIVERSAL

ADAPTERS

LUER-LOK

FITTINGS

Figure 1.--Solid-phase-extraction (SPE) vacuum manifold.

9.4 Weigh the sample bottle to three significant figures, and record the

gross sample weight. Add the methanol conditioner (1 percent of the sample

volume) to the sample, and record the initial sample weight. Add a 50-μL

aliquot of the terbuthylazine surrogate (5 ng/μL) using a micropipette with a

disposable glass capillary. Swirl the sample in the bottle to thoroughly

homogenize.

9.5 Place the inlet end of the Teflon-PFA tubing into the sample container,

and turn on the pump to displace all air from the tubing. Attach the in-line

filter (optional) and then the SPE cartridge, and begin collecting the sample

that is pumped through the cartridge. 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 or filter unit. Large air bubbles are a problem

because they can displace the methanol conditioner in the cartridge.
13

 CERAMIC-PISTON,

 VALVELESS

METERING PUMP

TUBE FITTING, 1/8-INCH

TO 1/4-INCH PIPE THREAD

TUBE TO

 LUER

UNION

(see detail below)

TUBE

UNION

Tefzel-ETFE female

luer connector

Tefzel-ETFE union

(1/8-inch diameter)

Tefzel-ETFE nut

Teflon-PFA tubing

(1/8-inch diameter)

1/4-28

thread

SPE

CARTRIDGE

SAMPLE

CONTAINER

CONTAINER FOR

EXTRACTED

SAMPLE

OPTIONAL

IN-LINE

FILTER UNIT

Figure 2.--Solid-phase-extraction (SPE) pumping apparatus.
14

9.6 Pump all of the sample through the SPE cartridge, and turn off the

pump when completed. Disconnect the cartridge from the pump system, and

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

extracted sample collected, and record the final weight of the sample

processed through the cartridge. Discard the extended sample, weigh the

empty sample bottle, and record the tare weight.

9.7 Rinse the pump and Teflon-PFA tubing with 50 mL methanol:

water (1:1) to prepare for the next sample.

9.8 Attach a universal adapter to the large, open end of the SPE

cartridge, then attach the adapter to the male Luer-Lok fitting on the gaspressure module of the solid-phase-extraction vacuum manifold (fig. 1), and

then dry the cartridge using a positive pressure (69 kPa for 15 minutes) of

high purity carbon dioxide to remove all interstitial water. High purity

nitrogen gas also can be used to dry the cartridge, but the necessary gas

pressure and drying time will need to be determined.

9.8.1 Elute the analytes by attaching a syringe needle to the LuerLok end of the SPE cartridge, positioning the needle and cartridge above a

1.8-mL vial (fig. 3), and then adding 1.8 mL of the elution solvent to the

cartridge and allowing the solvent to drain by gravity into the vial (about 5

minutes). Air pressure (using a 50-mL glass syringe) can be used to force any

interstitial solvent remaining in the cartridge into the vial.

9.8.2 Concentrate the eluant in the 1.8-mL vial to about 100 μL

under a gentle stream of nitrogen. At no time should the eluant be allowed

to go dry, because this might result in loss of analytes. Add a 10-μL aliquot of

the 5-ng/μL PAH internal-standard solution to the eluant, and extract 100 μL

of the eluant into a 100-μL vial for GC/MS analysis.

10. Calculation and reporting of results

10.1 Sample analysis and data evaluation

Ensure that GC/MS conditions for the analysis of the target

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 target-compound calibration data conform to the criteria in paragraph 7.2.

In addition, optimize the system so the reporting level for each target

compound can be achieved. Inject 2 μL of the sample extract and acquire data

using the GC/MS conditions described in paragraph 4.1.13.
15

1.8-milliliter vial

Stainless-steel

syringe needle,

16 gage

SPE cartridge

Vial rack

3-prong clamp

Figure 3.--Apparatus used for elution of analytes from solid-phase

extraction (SPE) cartridges by gravity flow.

10.2 Qualitative identification

10.2.1 The expected retention time (RT) of the GC peak of the

quantitation ion for the target compound of interest needs to be within ± 10

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 R T = expected retention time of the target compound or surrogate

compound;

RRTc = relative retention time of the target compound or surrogate

compound; and

RTi = uncorrected retention time of the quantitation ion of the

internal standard.
16

10.2.2 Mass-spectral verification for each target 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 in

paragraph 8. The relative ratios of the three ions need to be within ± 10

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

calibration solution.

10.3 Quantitation

10.3.1 If a target compound has passed the qualitative identification

criteria above, calculate the concentration in the sample as follows:

C = 

Ci x Ac x 1000

RFc x Ai x W , (4)

where C = concentration of the target 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 target compound or

surrogate compound identified;

RFc = factor for each target compound or surrogate compound

calculated above;

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

W = weight of the sample extract, expressed in milliliters (1.0 g =

1.0 mL).

10.3.2 The percent recovery of the surrogate compound is calculated

as follows:

R = 

Ci x Ac

RFc x Ai x Cs x Vs

 x 100 , (5)

where R = percent of recovery of the surrogate compound;

Ci = concentration of the corresponding internal standard, in

nanograms per sample;

Ac = area of the quantitation ion for the surrogate compound;
17

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 milliliters.

10.4 Reporting concentrations

Report concentrations of organonitrogen herbicides as follows: If

the concentration is less than the detection limit listed in table 2, report the

concentration as less than the detection limit; if the concentration is greater

than the detection limit, report the concentration to two significant figures.

METHOD PERFORMANCE

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

Platte River in Colorado, and a ground-water sample collected in Jefferson

County, Colo. (Arvada Well No. 14) were used to test the method

performance. Each of the three samples was split into two subsamples. One

set of three subsamples was fortified with 0.2 μg/L of each analyte and the

other set of three subsamples was fortified with 2.0 μg/L of each analyte.

Seven 100-mL aliquots of each of the six subsamples were analyzed in one

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

Accuracy and precision data from the analyses are presented in tables 3-8.

With these data, a method detection limit (MDL) was calculated for each

analyte using the formula:

MDL = S x t (n-1, 1-alpha = 0.99), (6)

where S = standard deviation of replicate analyses (micrograms per

liter) at the lowest concentration; and

n = number of replicate analyses.

t (n-1, 1-alpha = 0.99): Student's t value for the 99 percent

confidence level with n-1 degrees of freedom

(Eichelberger and others, 1988).
18

Table 3.--Accuracy and precision data from seven determinations of

the method analytes at 0.2 microgram per liter in reagent water

[conc., concentration; μg/L, microgram per liter]

Compound

Mean

observed

conc.

Standard

deviation

Relative

standard

deviation

Mean

accuracy

(percent of

Method

detection

limit

(μg/L) (μg/L) (percent) true conc.) (μg/L)

Butylate 0.081 0.014 17 41 0.052

Vernolate .105 .024 23 53 .090

Propachlor .164 .022 13 82 .080

Cycloate .142 .026 18 71 .096

Desisopropylatrazine .144 .010 7 72 .037

Desethylatrazine .165 .026 16 82 .096

Trifluralin .105 .004 4 52 .015

Simazine .162 .029 18 81 .109

Prometon .202 .019 9 101 .069

Atrazine .134 .024 18 67 .088

Propazine .133 .016 12 67 .059

Terbuthylazine .137 .014 11 68 .054

Terbacil .215 .025 11 107 .092

Metribuzin .177 .014 8 89 .052

Simetryn .168 .014 8 84 .050

Ametryn .174 .016 9 87 .060

Alachlor .203 .018 9 101 .067

Prometryn .178 .019 11 89 .070

Bromacil .301 .057 19 150 .213

Metolachlor .229 .026 11 114 .097

Cyanazine .219 .017 8 109 .063

Diphenamid .230 .022 10 115 .083

Butachlor .190 .023 12 95 .084

Carboxin .240 .017 7 120 .064

Hexazinone .248 .036 14 124 .132

Mean 0.178 0.021 12 89 0.079
19

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

method analytes at 2.0 micrograms per liter in reagent water

[conc., concentration; μg/L, microgram per liter]

Compound

Mean

observed

conc.

Standard

deviation

Relative

standard

deviation

Mean

accuracy

(percent of

(μg/L) (μg/L) (percent) true conc.)

Butylate 0.811 0.053 7 41

Vernolate 1.107 .032 3 55

Propachlor 1.470 .061 4 73

Cycloate 1.338 .048 4 67

Desisopropylatrazine .662 .073 11 33

Desethylatrazine 1.273 .072 6 64

Trifluralin .460 .045 10 23

Simazine 1.250 .057 5 62

Prometon 1.236 .076 6 62

Atrazine 1.230 .044 4 61

Propazine 1.233 .049 4 62

Terbuthylazine 1.300 .037 3 65

Terbacil 1.618 .174 11 81

Metribuzin 1.505 .092 6 75

Simetryn 1.188 .109 9 59

Ametryn 1.320 .054 4 66

Alachlor 1.459 .064 4 73

Prometryn 1.328 .060 5 66

Bromacil 1.214 .199 16 61

Metolachlor 1.504 .096 6 75

Cyanazine 1.207 .175 14 60

Diphenamid 1.591 .093 6 80

Butachlor 1.392 .078 6 70

Carboxin 1.523 .116 8 76

Hexazinone 1.528 .100 7 76

Mean 1.270 0.082 7 63
20

Table 5.--Accuracy and precision data from seven determinations of

the method analytes at 0.2 microgram per liter in surface water

(South Platte River)

[conc., concentration; μg/L, microgram per liter]

Compound

Mean

observed

conc.

Standard

deviation

Relative

standard

deviation

Mean

accuracy

(percent of

Method

detection

limit

(μg/L) (μg/L) (percent) true conc.) (μg/L)

Butylate 0.116 0.014 12 58 0.051

Vernolate .131 .026 20 66 .097

Propachlor .198 .010 5 99 .036

Cycloate .149 .011 8 74 .042

Desisopropylatrazine .144 .005 4 72 .020

Desethylatrazine .214 .052 24 107 .192

Trifluralin .124 .009 7 62 .032

Simazine .177 .009 5 88 .032

Prometon .235 .011 5 118 .041

Atrazine .151 .008 5 75 .028

Propazine .147 .008 6 74 .031

Terbuthylazine .156 .009 6 78 .034

Terbacil .300 .014 5 150 .053

Metribuzin .201 .010 5 101 .036

Simetryn .189 .009 5 94 .033

Ametryn .174 .009 5 87 .035

Alachlor .215 .011 5 107 .042

Prometryn .177 .017 10 88 .064

Bromacil .375 .026 7 187 .096

Metolachlor .244 .025 10 122 .093

Cyanazine .282 .022 8 141 .082

Diphenamid .260 .018 7 130 .066

Butachlor .252 .021 8 126 .079

Carboxin .260 .015 6 130 .056

Hexazinone .279 .017 6 139 .062

Mean 0.206 0.015 8 103 0.057
21

Table 6.--Accuracy and precision data from seven determinations of the

method analytes at 2.0 micrograms per liter in surface water

(South Platte River)

[conc., concentration; μg/L, microgram per liter]

Compound

Mean

observed

conc.

Standard

deviation

Relative

standard

deviation

Mean

accuracy

(percent of

(μg/L) (μg/L) (percent) true conc.)

Butylate 0.851 0.090 11 43

Vernolate 1.139 .090 8 57

Propachlor 1.498 .070 5 75

Cycloate 1.258 .107 9 63

Desisopropylatrazine .959 .107 11 48

Desethylatrazine 1.365 .104 8 68

Trifluralin .551 .046 8 28

Simazine 1.253 .069 6 63

Prometon 1.552 .081 5 78

Atrazine 1.217 .072 6 61

Propazine 1.207 .077 6 60

Terbuthylazine 1.263 .068 5 63

Terbacil 2.016 .065 3 101

Metribuzin 1.602 .042 3 80

Simetryn 1.394 .090 6 70

Ametryn 1.361 .077 6 68

Alachlor 1.433 .059 4 72

Prometryn 1.333 .080 6 67

Bromacil 1.590 .069 4 80

Metolachlor 1.569 .066 4 78

Cyanazine 1.579 .059 4 79

Diphenamid 1.593 .084 5 80

Butachlor 1.504 .084 6 75

Carboxin 1.556 .111 7 78

Hexazinone 1.745 .089 5 87

Mean 1.375 0.078 6 69
22

Table 7.--Accuracy and precision data from seven determinations of the method

analytes at 0.2 microgram per liter in ground water

(Arvada Well No. 14)

[conc., concentration; μg/L, microgram per liter]

Compound

Mean

observed

conc.

Standard

deviation

Relative

standard

deviation

Mean

accuracy

(percent of

Method

detection

limit

(μg/L) (μg/L) (percent) true conc.) (μg/L)

Butylate 0.104 0.024 23 52 0.090

Vernolate .141 .033 24 70 .123

Propachlor .179 .026 14 90 .095

Cycloate .151 .019 13 75 .072

Desisopropylatrazine .145 .008 5 72 .028

Desethylatrazine .153 .021 14 77 .078

Trifluralin .111 .051 46 55 .188

Simazine .169 .025 15 85 .093

Prometon .188 .032 17 94 .118

Atrazine .150 .026 17 75 .095

Propazine .150 .024 16 75 .090

Terbuthylazine .147 .027 18 74 .099

Terbacil .252 .068 27 126 .252

Metribuzin .194 .025 13 97 .095

Simetryn .193 .030 16 97 .111

Ametryn .190 .043 23 95 .159

Alachlor .196 .024 12 98 .088

Prometryn .188 .030 16 94 .112

Bromacil .379 .056 15 189 .208

Metolachlor .211 .028 13 106 .104

Cyanazine .221 .018 8 111 .068

Diphenamid .225 .041 18 113 .151

Butachlor .197 .022 11 99 .082

Carboxin .185 .027 15 93 .102

Hexazinone .219 .033 15 109 .122

Mean 0.186 0.030 17 93 0.113
23

Table 8.--Accuracy and precision data from seven determinations of the

method analytes at 2.0 micrograms per liter in ground water

(Arvada Well No. 14)

[conc., concentration; μg/L, microgram per liter; --, not detected]

Compound

Mean

observed

conc.

Standard

deviation

Relative

standard

deviation

Mean

accuracy

(percent of

(μg/L) (μg/L) (percent) true conc.)

Butylate 1.018 0.075 7 51

Vernolate 1.159 .090 8 58

Propachlor 1.518 .132 9 76

Cycloate 1.330 .103 8 67

Desisopropylatrazine .636 .060 9 32

Desethylatrazine 1.337 .112 8 67

Trifluralin .666 .112 17 33

Simazine 1.331 .077 6 67

Prometon 1.486 .124 8 74

Atrazine 1.253 .070 6 63

Propazine 1.305 .072 6 65

Terbuthylazine -- -- -- --

Terbacil 1.651 .101 6 83

Metribuzin 1.451 .155 11 73

Simetryn 1.427 .157 11 71

Ametryn 1.348 .145 11 67

Alachlor 1.433 .128 9 72

Prometryn 1.350 .136 10 67

Bromacil 1.378 .129 9 69

Metolachlor 1.539 .146 10 77

Cyanazine 1.219 .090 7 61

Diphenamid 1.503 .160 11 75

Butachlor 1.381 .150 11 69

Carboxin 1.297 .141 11 65

Hexazinone 1.647 .155 9 82

Mean 1.319 0.118 9 66
24

MDLs are sample-matrix and compound dependent. MDLs calculated

for reagent water at the 0.2 μg/L concentration range from 0.015 to 0.213 μg/L

and have a mean of 0.079 μg/L (table 3). For surface water (South Platte

River), MDLs calculated at the 0.2 μg/L concentration range from 0.020 to

0.192 μg/L, and have a mean of 0.057 μg/L (table 5). For ground water

(Arvada Well No. 14), MDLs calculated at the 0.2 μg/L concentration ranged

from 0.028 to 0.252 μg/L, and have a mean of 0.113 μg/L (table 7).

The mean accuracies (recoveries) of the analytes were sample-matrix and

concentration dependent. The mean accuracy of the analytes determined at

0.2 μg/L was 89 percent in reagent water (table 3), 103 percent in surface water

(South Platte River) (table 5), and 93 percent in ground water (Arvada Well

No. 14) (table 7). The mean accuracies of the method analytes determined at

2.0 μg/L were significantly less than at 0.2 μg/L (p < 0.001, Mann-Whitney

nonparametric test for two groups). The lesser recoveries at higher

concentrations could be the result of problems with adding the 2.0 μg/L

concentration solution mixture to the water samples. The relative concentration of water-immiscible solvent in the 2.0-μg/L concentration solution

mixture was 69 percent, compared to 25 percent in the 0.2-μg/L samples.

Solvent rinses of the sample bottles after the sample was pumped through

the cartridge might help determine if sorption losses to the sample container

was the cause of the lesser recoveries in the 2.0-μg/L concentration solution

mixture.

The method is ideally suited for using automated laboratory systems for

sample preparation. Preliminary testing of the method, with minor

modifications, has been conducted using a Waters Millilab Workstation. The

modifications included use of nitrogen, rather than carbon dioxide as a drying

gas, and use of Waters Sep-Pak cartridges, rather than the Analytichem

cartridges. The results indicated no significant differences in recovery of the

23 herbicides and 2 metabolites compared to the manual method described in

this report.

CONCLUSIONS

From the data presented, SPE with GC/MS in SIM is an efficient and

accurate method for determination of organonitrogen herbicides in

environmental water samples. Recoveries averaged 80 to 115 percent for the

23 herbicides and 2 metabolites in a reagent-water sample and 2 natural-water

samples fortified at levels of 0.2 and 2.0 micrograms per liter. The MDLs,

based on a 100-mL sample size, range from 0.015 to 0.252 microgram per liter,

and are dependent on sample matrix and specific herbicide.
25

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