STANDARD OPERATING PROCEDURE FOR THE ANALYSIS OF

CHLOROPHENOXY ACID HERBICIDES IN DRINKING WATER

(GC/EC. ESTERIFICATION)

CRL METHOD: EPA DN

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION 5 CENTRAL REGIONAL LABORATORY

536 SOUTH CLARK STREET (5SCRL)

CHICAGO,ILLINOIS 60605

DATE: Sept. 1990

CONCURRENCES:

TEAM LEADER:	Signed Erlinda Evangelista	9/19/90
SECTION CHIEF:	Signed Chi Tang	9/21/90
Q.C. COORDINATOR:	Signed James H. Adams, Jr.	9/24/90
CRL DIRECTOR:	Signed Charles T. Elly	9/24/90

 

 

STANDARD OPERATING PROCEDURE FOR THE ANALYSIS OF CHLOROPHENOXY

HERBICIDES IN DRINKING WATER

 

 

TABLE OF CONTENTS

SECTION	REV	DATE
1.0 SCOPE AND APPLICATION	0	9/90
2.0 SAFETY AND WASTE HANDLING	0	9/90
3.0 SUMMARY OF METHOD	0	9/90
4.0 SAMPLE HANDLING AND PRESERVATION	0	9/90
5.0 INTERFERENCES	0	9/90
6.0 APPARATUS AND MATERIALS	0	9/90
7.0 REAGENTS	0	9/90
8.0 INSTRUMENT CALIBRATION	0	9/90
9.0 PROCEDURE	0	9/90
10.0 CALCULATIONS	0	9/90
11.0 QUALITY CONTROL	0	9/90
12.0 INSTRUMENT MAINTENANCE	0	9/90
REFERENCES	0	9/90
ATTACHMENTS:Technical Informamation Bulletin Mini Diazald APPARATUS	0	9/90

 

STANDARD OPERATING PROCEDURE FOR THE ANALYSIS OF CHLOROPHENOXY

ACID HERBICIDES IN DRINKING WATER

 

1.0 SCOPE AND APPLICATION

1.1 This method covers the determination of chlorinated phenoxy acid herbicides in drinking water and raw source water. The compounds 2,4-dichlorophenoxy-acetic acid (2,4-D) and 2-(2,4,5- Trichlorophenoxy) propionic acid (Silvex) are determined by this procedure. It may also be applied to additional phenoxy acids such as 2,3-dichloro-o-anisic acid (Dicamba) and 2,4,5-Trichlorophenoxy-acetic acid (2,4,5-T) as well as certain phenols.

1.2 The method detection limits (MDL) are 0.05 ppb for silvex and 0.1 ppb for 2,4-D. The MDLs were determined using the procedure described in Appendix B to Part 136 of 40 CFR, October 26,1984.

1.3 Since these compounds may occur in various forms (i.e., acid, salt, ester. etc.) a hydrolysis step is included to permit the determination of the active part of the herbicide.

1.4 This method is restricted to use by or under the supervision of analysts experienced in extraction techniques, in handling diazomethane, in the use of a gas chromatograph and in the interpretation of gas chromatograms.

2.0 SAFETY AND WASTE HANDLING

2.1 The toxicity or carcinogenicity of each reagent used in this method has not been precisely defined; however, each chemical compound should be treated as a potential health hazard and exposure to these chemicals must be reduced to the lowest possible level by whatever means available.

2.2 Diazomethane is a carcinogen and can explode under certain conditions. Preparation and use of diazomethane should always be done in an efficient hood behind a safety shield. To prevent explosions, (a) do not heat solutions above 90 deg C; (b) store solutions away from alkali metals; (c) avoid ground glass apparatus, glass stirrers and sleeve bearings where grinding may occur. Solutions of diazomethane decompose rapidly in the presence of solid materials such as copper powder, calcium chloride, boiling chips, etc., therefore care should be taken to avoid contact with these materials.

2.3 Waste solvents must be disposed of according to approved safety and disposal protocols.

3.0 SUMMARY OF METHOD

3.1 A measured volume of water is acidified and the chlorinated phenoxyacids and their esters are extracted with ethyl ether. The extracts are treated with potassium hydroxide, hydrolyzed, and solvent-washed to remove extraneous organic material. The aqueous phase containing the herbicides is acidified and the phenoxyacids are then extracted with diethyl ether. The acids are converted to esters and analyzed by gas chromatography using electron capture detectors. Compound identification is confirmed using a second dissimilar column.

3.2 The method provides a Florisil column clean-up procedure to eliminate interferences that prevent qualitative and quantitative determination of the herbicides.

4.0 SAMPLE HANDLING AND PRESERVATION

4.1 Samples must be collected in amber glass bottles, 1 L capacity, fitted with Teflon lined screw caps. The sampler must ensure that contamination is kept to a minimum by thorough rinsing of equipments used and by avoiding the use of plastics and other potential sources of contamination.

4.2 All samples must be refrigerated at 4 deg C from the time of collection until extraction. The samples should be analyzed as soon after collection as possible. The maximum holding time for analysis of chlorophenoxyacid herbicides is 7 days after collection; however, well-stoppered and refrigerated extracts can be held up to 30 days.

5.0 INTERFERENCES

5.1 Solvents, reagents, glassware and other sample processing hardware may yield discrete artifacts and/or elevated baselines causing misinterpretation of gas chromatograms. All of these materials must be demonstrated to be free from interference under the conditions of the analysis by running laboratory blanks. Use only high purity reagents and solvents.

5.2 Glassware must be scrupulously cleaned. Clean all glassware as soon as possible after use by rinsing with the last solvent used in it, followed by detergent washing with hot water, and rinses with tap water and distilled water. The dry glassware is then heated in a drying oven at 400 deg C for about 30 min. ( An SOP for washing of labware at the CRL is available.) The glassware and glass wool used in this method should be acid- rinsed to prevent loss of the herbicides through reaction with alkaline substances that may be present.

5.3 The interferences encountered in drinking water should not pose great difficulty in obtaining accurate and precise measurement of chlorophenoxy acid herbicides.

5.4 Organic acids, especially chlorinated acids, cause the most direct interference with the determination. Phenols, including chlorophenols, will also interfere with this procedure.

5.4 Alkaline hydrolysis and subsequent extraction eliminates many of the predominant chlorinated insecticides which might otherwise interfere with the test.

6.0 APPARATUS AND MATERIALS

6.1 Glassware

Note: The glassware used for diazomethane generation should have clear joints; the use of glassware with ground-glass joints is prohibited to prevent explosions.

6.1.1 Separatory funnel- 60 ml and 2000 ml with Teflon stopcock

6.1.2 Erlenmeyer flask- 125 ml, 250 ml with stoppers

6.1.3 Kuderna-danish (K-D) assembly consisting of:

6.1.3.1 Evaporative flask (K-D flask)- 250 ml. Attach to concentrator tubes with springs.

6.1.3.2 Concentrator tubes (K-D receivers) - 10 ml graduated with stopper.

6.1.3.3 Snyder columns - 3 ball macro or 2 ball micro

6.1.4 Microsyringes - 10 uL

6.1.5 Pipets - disposable., Pasteur type

6.1.6 Volumetric pipets - Class A, l-, 2- or 5- ml capacity

6.1.7 Volumetric flasks - 10) mi, 50 ml, 100 ml

6.1.8 Graduated cylinders L. 100 mi. 250) ml

6.2 Glass wool - filtering grade, acid-washed

6.3 Diazald Kit and Mini Diazald Apparatus - recommended for the generation of diazomethane:( Available from Aldrich Chem. Co.)

6.4 Boiling chips - solvent extracted, approximately 10/40 mesh, silicon carbide or equivalent

6.5 Analytical Balance capable of accurately weighing 0.0001 g

6.6 Gas Chromatograph An analytical system complete with Gas Chromatograph (GC) suitable for on column injections and all required accessories including electron capture detectors, column supplies, gases and an autosampler. A data system should be used for data acquisition and processing.

6.6.1 HP 5890A GC equipped with 2 on-column 1/4 in. injectors, 2 electron capture detectors, dual- column capability oven

6.6.2 TRACOR 540 GC equipped with 2 glass lined injection ports, 2 electron capture detectors, dual-column capability oven

6.7 Gas chromatographic columns:

6.7.1 Packed column chromatography

6.7.1.1 Primary column: 1.5% SP-2250/1.95% SP-2401 on 100/120 mesh Supelcoport packed in an 8 ft x 1/4 in OD x mm(or 4 mm) ID glass column; or equivalent

6.7.1.2 Confirmatory column: 3% SP-2100 on 100/120 mesh Supelcoport packed in an 8 ft x 1/4 in OD x 2 mm (or 4 mm) ID glass column; or equivalent

6.7.2 Capillary column chromatography

6.7.2.1 Primary column: DB-608, 30 m x 0.53 mm ID x 0.83 uM film thickness

6.7.2.2 Confirmatory column: DB-S, 30 m x 0.53 mm ID x 1.5 uM film thickness

6.8 S-EVAP Analytical evaporator - with temperature control; operating instruction manual should be available

6.9 N-EVAP Analytical evaporator - with temperature control; connected to a supply of pure nitrogen for blowing down sample extracts

7.0 REAGENTS

7.1 Reagent water - defined as water in which an interferent is not observed at the MDL of the parameter of interest

7.2 Solvents:

7.2.1 Hexane pesticide quality

7.2.2 Acetone pesticide quality

7.2.3 Benzene - pesticide quality

7.2.4 Isooctane - pesticide quality

7.2.5 Diethyl ether - pesticide quality or equivalent; unpreserved. Must be free of peroxides as indicated by EM Quant test strips (Available from EM Laboratories, Inc., 500 Executive Blvd., Elmsford, N. Y., 10523). Procedures for the removal of peroxides are provided with the test-strips.

7.3 Carbitol - diethylene glycol monoethyl ether; ACS, available from Aldrich Chemical Co.

7.4 N-methyl-N-nitroso-p-toluenesulfonamide (Diazaid) - High purity, melting point range 60 - 62 deg C. Precursor for the generation of diazomethane. Available from Aldrich Chem. Co.

7.5 Potassium Hydroxide solution - 37% (w:v) aqueous solution prepared from reagent grade potassium hydroxide pellets and reagent water.

7.6 Sulfuric acid, conc. - ACS; reagent grade, Sp. Gr. 1.84

7.6.1 Sulfuric acid, ( 1:3 ) - Add 1 volume of conc. sulfuric acid, carefully, in small increments, to 3 volumes of water. Cool while adding acid. (Caution: Never add water to acid.)

7.7 Sodium Sulfate, Aciditied - ACS; granular sodium sulfate treated as follows: Add 1 ml of 1:3 sulfuric acid to 100 g of sodium sulfate slurried with enough ethyl ether to just cover the solid. Remove the ether with the vacuum. Mix 1 g of the resulting solid with S mi of reagent water and ensure the mixture to have a pH of 4. Store at 130 deg C.

7.8 Florisil - PR grade (60 - 100 mesh) Purchase activated at 1250 deg F and stored at 130 deg C.

7.9 Standards - 2,4-D methyl ester and Silvex methyl ester, crystals; purchased from Supelco

7.9.1 Stock Standards: Prepare stock standards by accurately weighing out 10 mg of 2,4-D methyl ester and 12 mg of Silvex methyl ester. Dissolve each methyl ester in separate 50 ml volumetric flasks and dilute to the mark with isooctane. Store at 4 deg C. Check frequently for signs of degradation or evaporation. The concentrations are as follows:

2,4-D methyl ester - 200 ug/ml

Silvex methyl ester - 240 ug/ml

7.9.2 Intermediate Standards: Using a class A volumetic pipet, transfer 1.0 ml of 2,4-D methyl ester stock standard and 0.45 ml of silvex methyl ester stock standard into a 100 ml volumetric flask. dilute to the mark with isooctane and mix well. The concentrations of esters in the intermediate mix are as follows:

2,4-D methyl ester - 2.0 ug/ml

Silvex methyl ester - 1.08 ug/ml

7.9.3 Calibration standards (Working): Prepare 5 calibration levels of the standard mix by serially diluting the intermediate standard as outlined in the table below. Use hexane as the diluting solvent. Store these standards in the refrigerator at 4 deg C. These calibration levels correspond to the linear range of the detector.

 

Level	Vol. Int.	Final Volume	Silvex ug/ml	2,4-D ug/ml
1	1.0 ml	200 ml	.005	.010
2	1.0 ml	100 ml	.011	.020
3	2.0 ml	100 ml	.023	.040
4	3.5 ml	100 ml	.038	.070
5	5.0 ml	100 ml	.054	.100

7.9.4 Spiking solution: Pipet 10 ml of the intermediate standard mix into a 50 ml volumetric flask and dilute to the mark with hexane. The solution contains 0.21 ug/ml of silvex and 0.40 ug/ml of 2,4-D.

8.0 INSTRUMENT CALIBRATION

8.1 Establish gas chromatographic operating conditions as follows:(Note: Any changes in these conditions will have to be validated and properly, documented.)

Injector Temperature - 25O deg C

Column Temperature - 180 deg C

Detector Temperature - 350 deg C

Carrier Gas - Nitrogen, ultra-high purity

Flow rate - ca. 26 ml/min

8.2 Calibrate the gas chromatographic system by injecting 5 uL of each calibration standard described in 7.9.3 into the GC. Acquire and process data using the Nelson Chromatography Data System (Model 2600).

8.3 Prepare an external standard calibration method for the herbicide standard mix to be used in processing the data acquired. This is done by tabulating the responses (peak areas or heights) against the amount of each component in the standard mix using the method development software of the data system. The system then plots a calibration curve of amount versus area and uses this curve for quantitation. The concentrations of each component in the standard mix should have been previously verified to be within the linear range of the detector. The calibration curves should be linear and should reflect known detector capabilities and response characteristics. Acceptable correlation coefficient is better than 0.995.

8.4 Verify the working calibration curve or calibration factor on each working day by injection of one or more calibration standards. The response for each component should not vary from the predicted response by more than 15 If it does, a new calibration curve must be prepared.

8.5 Run a continuing calibration by injecting a mid-level standard mix after every 5 sample extracts. Check the response against the initial five point calibration curve. The % RPD should be less than 10 %. If the % RPD is >10 %, recalibrate and reanalyze all samples that are positive for any parameter of interest. If % RPD is >20 %, reanalyze all samples.

8.6 Establish retention time (RT) windows by calculating the standard deviation (SD) of the absolute retention times of the individual components obtained from multiple injections of the standard mix within a run sequence or a 24 hr period whichever is shorter. Plus or minus three times the SD for each component will be used to define the retention time window. The laboratory must determine RT windows for each standard component for every column/detector system on each GC. These RT windows are used for qualitative determinations; positive identification is based on RT comparisons of the peaks in the sample chromatogram with those of the peaks in standard chromatograms on two dissimilar columns.

9.0 PROCEDURE

9.1 Sample Extraction

NOTE: Refer to Section 11 (Quality Control) for the associated QC samples and spiking solutions. The QC samples should be carried through the entire analytical procedure.

9.1.1 Mark the water meniscus on the side of the sample bottle for later determination of the sample volume. Pour the entire sample into a 2-L separatory funnel and check the pH with wide range pH paper. Acidify to approximately pH 2 with 1:3 sulfuric acid.

9.1.2 Add 150 ml of diethyl ether to the sample in the separatory funnel and shake vigorously for I min. Allow the contents to separate for at least 10 min. If an emulsion forms between the layers and the size is more than 1/3 of the solvent layer, the analyst must employ mechanical techniques to complete the phase separation. The optimum technique depends upon the sample but may include stirring, filtration of the emulsion through glass wool, centrifugation or other physical methods.

9.1.3 After the layers have separated, drain the water phase into a I L Erlenmeyer flask. Collect the ether extract in a 250 ml ground glass Erlenmeyer flask containing 2 ml of 37 % aqueous potassium hydroxide.

9.1.4 Pour the water sample back into the separatory funnel and extract two more times using 50 ml of ether each time. Combine the extracts in the Erlenmeyer flask. (Rinse the 1 L flask with each additional aliquot of extracting solvent.)

9.1.5 Determine the original sample volume by refilling the sample bottle to the mark with water and transferring to a 1000 ml graduated cylinder. Record the sample volume to the nearest five ml.

9.2 Hydrolysis

9.2.1 Add 15 ml of distilled water and one or two clean boiling chips to the flask containing the ether extract and attach a 3- ball snyder column. Evaporate the ether on the S-EVAP and continue heating for a total of 60 min.

9.2.2 Transfer the concentrate to a 60 mi separatory funnel. Extract the basic solution twice with 0"0 ml of ether and discard the ether layers. (Note: dispose of ether properly according to safety protocols.) The herbicides remain 4 n in the aqueous phase.

9.3 Solvent Clean-up and Sample concentration (K-D)

9.3.1 Acidify the contents of the separatory funnel by adding 2 ml of cold ( 4 deg C ) 1:3 sulfuric acid. Extract the herbicides once with 20 ml of ether and two more times with 10 ml of ether each time. Collect the extracts in a 125 ml Erlenmeyer flask containing about 0.5 g of acidified anhydrous sodium sulfate. Allow the extract to remain in contact with the sodium sulfate for approximately 2 hours.

9.3.2 Transfer the ether extract, through a funnel plugged with acid washed glass wool, into a K-D flask equipped with a 10 ml receiver. Rinse the Erlenmeyer flask with 20 - 30 ml of ether to complete the quantitative transfer. Use a glass rod to crush any caked sodium sulfate during the washing.

9.3.3 Add one or two clean boiling chips to the K-D flask and attach a three ball Snyder column. Prewet the Snyder column by adding about 1 ml of ether to the top. Place the K-D assembly on the S-EVAP analytical evaporator at 60 - 65 deg C, with the receiver partially immersed in the water and the entire lower rounded surface of the K-D flask is bathed in hot vapor. When the apparent volume reaches about 1 ml, remove the K-D apparatus for the S-EVAP and allow it to drain and cool for at least 10min.

9.3.4 Rinse the flask and its lower joints into the receiver with small portions of ether and adjust the volume to approximately 4 ml. Proceed with the esterification using a solution of diazomethane prepared by the Diazald kit method. (See the attached Mini-Diazald Apparatus Technical Information Bulletin for the diazomethane preparation procedure.)

9.4 Esterification

9.4.1 Add 2 ml of diazomethane solution to the extract in the receiver and let stand for 10 min with occasional swirling.

9.4.2 Rinse the inside wall of the receiver with several hundred uL of ether. Take sample to approximately 2 ml to remove excess diazomethane by allowing the solvent to evaporate spontaneously at room temperature.

9.4.3 Dissolve the residue in 5 ml of hexane and dilute to a final volume of 10 ml. Analyze by gas chromatography. If interferences are present, as seen from the chromatograms, further clean-up is required. Proceed with the Florisil clean-up procedure.

9.5 Florisil Clean-up: Before using this procedure, verify the elution pattern and the absence of interferences from reagents.

9.5.1 Prepare a column of Florisil by plugging a disposable Pasteur pipet with glass wool and packing with 2.0 cm of sodium sulfate over 1.5 cm of Florisil adsorbent.

9.5.2 Elute the esterified extract in the receiver through the column, collecting the eluates in a 10 ml graduated ampul. Complete the transfer by repeatedly rinsing the receiver with small portions of hexane and passing the rinses through the column until a final volume of 10 ml of eluate is obtained.

9.5.3 Proceed with the gas chromatographic analysis.

9.6 Gas Chromatography

9.6.1 Before proceeding with the analysis, ensure that the instrument has been calibrated properly according to Section 8.

9.6.2 Place the sample extracts or dilutions of the extracts, calibration standards, continuing calibration standards, and the associated QC samples into the appropriate autosampler vials and label each vial correctly.

9.6.3 Load the sample vials on the autosampler in the order that they appear on a previously prepared batch data acquisition sequence file. The sequence would generally start with a solvent run, initial calibration standards, followed by the QC samples and the samples. A continuing calibration must be run after every five extract injections.

9.6.4 Start the GC run following the appropriate procedure for making gas chromatographic runs using the Nelson Chromatography Data System 2600.

9.6.5 Monitor the run to ensure that the system is in control. Should problems become apparent, do corrective action before proceeding with the run. If the 10 % RPD criteria for peak area responses is exceeded, inspect the GC system to determine the cause and perform whatever maintenance is necessary before recalibrating and proceeding with the sample analysis.

9.6.6 Process the data acquired using the calibration method prepared for the standard mix. Identify the parameters in the sample by comparing the retention times of the peaks in the sample chromatograms with those of the standard chromatograms. Confirm the identification on the second column. Perform the calculations according to Section 10.

9.6.7 If the QC results are outside the limits, determine the cause, take corrective action and re-run as necessary.

10.0 CALCULATIONS

10.1 The data system derives the concentrations of the methyl esters from the calibration curves generated during method development which generally follows the equations below for manual calculations.

Cc in uG/L (ppb) = RF x Ac x Dilution Factor

                                         V sample

where:

RF- Response factor for the compound

Cc - Concentration of the compound

Ac - Area response for the compound

V - Volume of sample

 

RF =       Amount of compound     

           Area response for compound

10.2 To convert the methyl ester concentrations into their acid equivalents, multiply the methyl ester concentration by the ratio of the molecular weight of acid t o molecular weight of ester. The molecular weights of the methyl esters and their acid equivalents are given below:

2,4-D	222	Silvex	269.5
2,4-D methyl ester	236	Silvex methyl ester	283.5

Conc of Acid   =     Conc of ester   x    Molecular weight acid

                                                           Molecular weight ester

11.0 QUALITY CONTROL

11.1 The laboratory is required to operate a formal quality control program. The minimum requirements of this program consist of an initial demonstration of laboratory capability and an ongoing analysis not method blanks, spiked samples and laboratory control standards to evaluate and document data quality. Ongoing data quality checks are compared with established performance criteria to determine if the results of the analysis meet the criteria.

11.1.1 Method blank: The method blank is carried through the entire procedure. It should be free of contamination by parameters of interest. A method blank is analyzed for every set of samples or each day of extraction.

11.1.2 Matrix spike/matrix spike duplicate: The matrix spike and matrix spike duplicate are carried through the entire procedure and the recovery results are compared with the established limits. The relative percent difference (RPD) between duplicate spikes is calculated and is a measure of method precision. The sample designated by the site as the MS/MSD are spiked as follows: Add 1 ml of the spiking solution (7.9.4) to 1 liter of water sample.

11.1.3 Duplicate samples : A sample will be analyzed in duplicate.

11.2 Quality control charts should be developed and used to determine if the analysis is in control. If not, investigate the possible cause of the problem and initiate corrective action.

12.0 INSTRUMENT MAINTENANCE

12.1 It is the responsibility of every analyst to make sure that the gas chromatographic system is properly maintained. The following precautionary measures for preventive maintenance are recommended:

12.1.1 Use only ultra-high purity carrier gases. Install moisture, hydrocarbon and oxygen traps along the gas line and replace them periodically. Set the pressure regulator at 80 psi and change the carrier gas tank when the pressure gauge indicates 400 psi. Before installing a new tank of carrier gas, ensure that the valve opening is free from any dirt that may adversely affect the carrier gas lines. Clean if necessary before connecting the regulator.

12.1.2 Make sure there are no leaks in the system. Check the flow through the detector using a bubble flowmeter and ensure that the right flow is maintained.

12.1.3 Use only preconditioned columns. Install the column according to GC manufacturer recommended column installation procedure. Monitor for- active sites formation and initiate remedial actions such as baking-out the column (check maximum allowable temperatures), removing any foreign materials (such as broken glass from the rim of the column or pieces of septa), replacing the glass wool and /or the first few millimeters or longer, of the packing material at the injector end of the column, swabbing out the inside walls of the column if any residue is noted, and silanizing the column. (Note: Follow proper silanizing procedures.) If all of these fail, replace the column.

12.1.4 Replace the injection port septum periodically; ideally, every 30 injections. Use only the proper size, Teflon-backed, high temperature, low bleed septa and make sure there is a carrier gas septum purge (about 2 ml/min) when using the HP5890A GC. The injection port might have to be baked out occasionally 20 deg C higher than the operating temperature.

12.1.5 Thermally clean the detectors at the first sign of increased background signal. (Recommended bake-out temperature is 390 deg C for at least 12 hours or until the signal comes back to normal but not over 24 hours. HP5890A detectors' normal background signal when clean is below 50 on the instrument front display panel or about 45000 plus or minus 5000 uv low value as shown when data points are plotted using the Nelson Chromatography System 2600.) If this fails, the detectors have to be sent out for factory cleaning.

12.1.6 Major maintenance procedures should be done by expert GC manufacturer service personnel.

 

REFERENCES

1. " Method for Organochlorine Pesticides and Chlorophenoxy Acid Herbicides in Drinking Water and Raw Source Water ". Available from ORD Publications, CERI, EPA. Cincinnati, Ohio 45268; EPA 600/4-81-O53; pp 20 - 35

2. "Method 8150, Chlorinated Herbicides , SW 846 - Sept. 1986

SEE QA/QC COORDINATOR FOR TECHNICAL INFORMATION BULLETIN