EPA 1624.1

METHOD 1624 REVISION B—VOLATILE ORGANIC COMPOUNDS BY

ISOTOPE DILUTION GC/MS

1.1.1

Scope and Application

This method is designed to determine the volatile toxic organic pollutants associated withthe 1976 Consent Decree and additional compounds amenable to purge and trap gaschromatography-mass spectrometry (GC/MS).

The chemical compounds listed in Table 1 may be determined in municipal andindustrial discharges by this method. The method is designed to meet the surveyrequirements of Effluent Guidelines Division (EGD) and the National PollutantsDischarge Elimination System (NPDES) under 40 CFR Parts 136.1 and 136.5. Anymodifications of this method, beyond those expressly permitted, shall be considered asmajor modifications subject to application and approval of alternate test proceduresunder 40 CFR Parts 136.4 and 136.5.

The detection limit of this method is usually dependent on the level of interferencesrather than instrumental limitations. The limits in Table 2 represent the minimumquantity that can be detected with no interferences present.

The GC/MS portions of this method are for use only by analysts experienced withGC/MS or under the close supervision of such qualified persons. Laboratories unfamiliarwith the analyses of environmental samples by GC/MS should run the performance testsin Reference 1 before beginning.Summary of Method

Stable isotopically labeled analogs of the compounds of interest are added to a 5 mLwater sample. The sample is purged at 20-25°C with an inert gas in a specially designedchamber. The volatile organic compounds are transferred from the aqueous phase intothe gaseous phase where they are passed into a sorbent column and trapped. Afterpurging is completed, the trap is backflushed and heated rapidly to desorb thecompounds into a gas chromatograph (GC). The compounds are separated by the GCand detected by a mass spectrometer (MS) (References 2 and 3). The labeled compoundsserve to correct the variability of the analytical technique.

Identification of a compound (qualitative analysis) is performed by comparing the GCretention time and the background corrected characteristic spectral masses with those ofauthentic standards.

Quantitative analysis is performed by GC/MS using extracted ion current profile (EICP)areas. Isotope dilution is used when labeled compounds are available; otherwise, aninternal standard method is used.

Quality is assured through reproducible calibration and testing of the purge and trap andGC/MS systems.

1.2

1.3

1.4

2.2.1

2.2

2.3

2.4

3.3.1

Contamination and Interferences

Impurities in the purge gas, organic compounds out-gassing from the plumbing upstreamof the trap, and solvent vapors in the laboratory account for the majority ofcontamination problems. The analytical system is demonstrated to be free frominterferences under conditions of the analysis by analyzing blanks initially and with eachsample lot (samples analyzed on the same eight hour shift), as described in Section 8.5.Samples can be contaminated by diffusion of volatile organic compounds (particularlymethylene chloride) through the bottle seal during shipment and storage. A field blankprepared from reagent water and carried through the sampling and handling protocolserves as a check on such contamination.

Contamination by carry-over can occur when high level and low level samples areanalyzed sequentially. To reduce carry-over, the purging device and sample syringe arerinsed between samples with reagent water. When an unusually concentrated sampleis encountered, it is followed by analysis of a reagent water blank to check for carry-over.For samples containing large amounts of water soluble materials, suspended solids, highboiling compounds, or high levels or purgeable compounds, the purge device is washedwith soap solution, rinsed with tap and distilled water, and dried in an oven at100-125°C. The trap and other parts of the system are also subject to contamination;therefore, frequent bakeout and purging of the entire system may be required.Interferences resulting from samples will vary considerably from source to source,depending on the diversity of the industrial complex or municipality being sampled.Safety

The toxicity or carcinogenicity of each compound or reagent used in this method has notbeen precisely determined; however, each chemical compound should be treated as apotential health hazard. Exposure to these compounds should be reduced to the lowestpossible level. The laboratory is responsible for maintaining a current awareness file ofOSHA regulations regarding the safe handling of the chemicals specified in this method.A reference file of data handling sheets should also be made available to all personnelinvolved in these analyses. Additional information on laboratory safety can be found inReferences 4 through 6.

The following compounds covered by this method have been tentatively classified asknown or suspected human or mammalian carcinogens: benzene, carbon tetrachloride,chloroform, and vinyl chloride. Primary standards of these toxic compounds should beprepared in a hood, and a NIOSH/MESA approved toxic gas respirator should be wornwhen high concentrations are handled.Apparatus and Materials

Sample bottles for discrete sampling.5.1.1

Bottle—25-40 mL with screw cap (Pierce 13075, or equivalent). Detergent wash,rinse with tap and distilled water, and dry at >105°C for one hr minimum beforeuse.

3.2

3.3

3.44.4.1

4.2

5.5.1

5.1.2

5.2

Septum—Teflon-faced silicone (Pierce 12722, or equivalent), cleaned as above andbaked at 100-200°C, for one hour minimum.

Purge and trap device—consists of purging device, trap, and desorber. Complete devicesare commercially available.5.2.1

Purging device—designed to accept 5 mL samples with water column at least 3cm deep. The volume of the gaseous head space between the water and trap shallbe less than 15 mL. The purge gas shall be introduced less than 5 mm from thebase of the water column and shall pass through the water as bubbles with adiameter less than 3 mm. The purging device shown in Figure 1 meets thesecriteria.

Trap—25-30 cm x 2.5 mm i.d. minimum, containing the following:

5.2.2.1Methyl silicone packing—one ±0.2 cm, 3% OV-1 on 60/80 mesh

Chromosorb W, or equivalent.5.2.2.2Porous polymer—15 ±1.0 cm, Tenax GC (2,6-diphenylene oxide polymer),

60/80 mesh, chromatographic grade, or equivalent.5.2.2.3Silica gel—8 ±1.0 cm, Davison Chemical, 35/60 mesh, Grade 15, or

equivalent. The trap shown in Figure 2 meets these specifications.

5.2.3

Desorber—shall heat the trap to 175 ±5°C in 45 seconds or less. The polymersection of the trap shall not exceed 180°C, and the remaining sections shall notexceed 220°C. The desorber shown in Figure 2 meets these specifications.The purge and trap device may be a separate unit or coupled to a GC as shownin Figures 3 and 4.

5.2.2

5.2.4

5.3

Gas chromatograph—shall be linearly temperature programmable with initial and finalholds, shall contain a glass jet separator as the MS interface, and shall produce resultswhich meet the calibration (Section 7), quality assurance (Section 8), and performancetests (Section 11) of this method.5.3.1

Column—2.8 ±0.4 m x 2 ±0.5 mm i. d. glass, packed with 1% SP-1000 onCarbopak B, 60/80 mesh, or equivalent.

5.4

Mass spectrometer—70 eV electron impact ionization; shall repetitively scan from 20-250amu every two to three seconds, and produce a unit resolution (valleys between m/z174-176 less than 10% of the height of the m/z 175 peak), background corrected massspectrum from 50 ng 4-bromo-fluorobenzene (BFB) injected into the GC. The BFBspectrum shall meet the mass-intensity criteria in Table 3. All portions of the GCcolumn, transfer lines, and separator which connect the GC column to the ion sourceshall remain at or above the column temperature during analysis to precludecondensation of less volatile compounds.

5.5

Data system—shall collect and record MS data, store mass intensity data in spectrallibraries, process GC/MS data and generate reports, and shall calculate and recordresponse factors.5.5.15.5.2

Data acquisition—mass spectra shall be collected continuously throughout theanalysis and stored on a mass storage device.

Mass spectral libraries—user created libraries containing mass spectra obtainedfrom analysis of authentic standards shall be employed to reverse search GC/MSruns for the compounds of interest (Section 7.2).

Data processing—the data system shall be used to search, locate, identify, andquantify the compounds of interest in each GC/MS analysis. Software routinesshall be employed to compute retention times and EICP areas. Displays ofspectra, mass chromatograms, and library comparisons are required to verifyresults.

Response factors and multipoint calibrations—the data system shall be used torecord and maintain lists of response factors (response ratios for isotope dilution)and generate multi-point calibration curves (Section 7). Computations of relativestandard deviation (coefficient of variation) are useful for testing calibrationlinearity. Statistics on initial and on-going performance shall be maintained(Sections 8 and 11).

5.5.3

5.5.4

5.65.75.85.95.105.116.6.1

Syringes—5 mL glass hypodermic, with Luer-lok tips.Micro syringes—10, 25, and 100 µL.

Syringe valves—Two-way, with Luer ends (Teflon or Kel-F).Syringe—5 mL, gas-tight, with shut-off valve.Bottles—15 mL, screw-cap with Teflon liner.Balance—analytical, capable of weighing 0.1 mg.Reagents and Standards

Reagent water—water in which the compounds of interest and interfering compoundsare not detected by this method (Section 11.7). It may be generated by any of thefollowing methods:6.1.16.1.2

Activated carbon—pass tap water through a carbon bed (Calgon Filtrasorb-300,or equivalent).

Water purifier—pass tap water through a purifier (Millipore Super Q, orequivalent).

6.1.3

Boil and purge—heat tap water to 90-100°C and bubble contaminant free inert gasthrough it for approx one hour. While still hot, transfer the water to screw-capbottles and seal with a Teflon-lined cap.

6.26.36.4

Sodium thiosulfate—ACS granular.Methanol—pesticide quality or equivalent.

Standard solutions—purchased as solution or mixtures with certification to their purity,concentration, and authenticity, or prepared from materials of known purity andcomposition. If compound purity is 96% or greater, the weight may be used withoutcorrection to calculate the concentration of the standard.

Preparation of stock solutions—prepare in methanol using liquid or gaseous standardsper the steps below. Observe the safety precautions given in Section 4.6.5.1

Place approx 9.8 mL of methanol in a 10 mL ground glass stoppered volumetricflask. Allow the flask to stand unstoppered for approximately 10 minutes or untilall methanol wetted surfaces have dried. In each case, weigh the flask,immediately add the compound, then immediately reweigh to preventevaporation losses from affecting the measurement.

6.5.1.1Liquids—using a 100 µL syringe, permit two drops of liquid to fall into

the methanol without contacting the leck of the flask. Alternatively, injecta known volume of the compound into the methanol in the flask using amicro-syringe.6.5.1.2Gases (chloromethane, bromomethane, chloroethane, vinyl chloride)—fill

a valved 5 mL gas-tight syringe with the compound. Lower the needle toapproximately 5 mm above the methanol meniscus. Slowly introduce thecompound above the surface of the meniscus. The gas will dissolverapidly in the methanol.

6.5.2

Fill the flask to volume, stopper, then mix by inverting several times. Calculatethe concentration in mg/mL (µg/µL ) from the weight gain (or density if aknown volume was injected).

Transfer the stock solution to a Teflon sealed screw-cap bottle. Store, withminimal headspace, in the dark at -10 to -20°C.

Prepare fresh standards weekly for the gases and 2-chloroethylvinyl ether. Allother standards are replaced after one month, or sooner if comparison with checkstandards indicate a change in concentration. Quality control check standardsthat can be used to determine the accuracy of calibration standards are availablefrom the US Environmental Protection Agency, Environmental Monitoring andSupport Laboratory, Cincinnati, Ohio.

6.5

6.5.36.5.4

6.6

Labeled compound spiking solution—from stock standard solutions prepared as above,or from mixtures, prepare the spiking solution to contain a concentration such that a 5-10µL spike into each 5 mL sample, blank, or aqueous standard analyzed will result in a

concentration of 20 µg/L of each labeled compound. For the gases and for the watersoluble compounds (acrolein, acrylonitrile, acetone, diethyl ether, and MEK), aconcentration of 100 µg/L may be used. Include the internal standards (Section 7.5) inthis solution so that a concentration of 20 µg/L in each sample, blank, or aqueousstandard will be produced.

6.7

Secondary standards—using stock solutions, prepare a secondary standard in methanolto contain each pollutant at a concentration of 500 µg/mL. For the gases and watersoluble compounds (Section 6.6), a concentration of 2.5 mg/mL may be used.6.7.1

Aqueous calibration standards—using a 25 µL syringe, add 20 µL of thesecondary standard (Section 6.7) to 50, 100, 200, 500, and 1000 mL of reagentwater to produce concentrations of 200, 100, 50, 20, and 10 µg/L, respectively.If the higher concentration standard for the gases and water soluble compoundswas chosen (Section 6.6), these compounds will be at concentrations of 1000, 500,250, 100, and 50 µg/L in the aqueous calibration standards.

Aqueous performance standard—an aqueous standard containing all pollutants,internal standards, labeled compounds, and BFB is prepared daily, and analyzedeach shift to demonstrate performance (Section 11). This standard shall containeither 20 µg/L or 100 µg/L of the labeled and pollutant gases and water solublecompounds, 10 µg/L BFB, and 20 µg/L of all other pollutants, labeledcompounds, and internal standards. It may be the nominal 20 µg/L aqueouscalibration standard (Section 6.7.1).

A methanolic standard containing all pollutants and internal standards isprepared to demonstrate recovery of these compounds when syringe injection andpurge and trap analyses are compared. This standard shall contain either 100µg/mL or 500 µg/mL of the gases and water soluble compounds, and 100 µg/mLof the remaining pollutants and internal standards (consistent with the amountsin the aqueous performance standard in Section 6.7.2).

Other standards which may be needed are those for test of BFB performance(Section 7.1) and for collection of mass spectra for storage in spectral libraries(Section 7.2).

6.7.2

6.7.3

6.7.4

7.7.1

Calibration

Assemble the gas chromatographic apparatus and establish operating conditions givenin Table 2. By injecting standards into the GC, demonstrate that the analytical systemmeets the detection limits in Table 2 and the mass-intensity criteria in Table 3 for 50 ngBFB.

Mass spectral libraries—detection and identification of the compound of interest aredependent upon the spectra stored in user created libraries.7.2.1

Obtain a mass spectrum of each pollutant and labeled compound and eachinternal standard by analyzing an authentic standard either singly or as part ofa mixture in which there is no interference between closely eluted components.That only a single compound is present is determined by examination of the

7.2

spectrum. Fragments not attributable to the compound under study indicate thepresence of an interfering compound. Adjust the analytical conditions and scanrate (for this test only) to produce an undistorted spectrum at the GC peakmaximum. An undistorted spectrum will usually be obtained if five completespectra are collected across the upper half of the GC peak. Software algorithmsdesigned to “enhance” the spectrum may eliminate distortion, but may alsoeliminate authentic m/z’s or introduce other distortion.

7.2.37.2.4

The authentic reference spectrum is obtained under BFB tuning conditions(Section 7.1 and Table 3) to normalize it to spectra from other instruments.The spectrum is edited by saving the five most intense mass spectral peaks andall other mass spectral peaks greater than 10% of the base peak. This spectrumis stored for reverse search and for compound confirmation.

7.3

Assemble the purge and trap device. Pack the trap as shown in Figure 2 and conditionovernight at 170-180°C by backflushing with an inert gas at a flow rate of 20-30 mL/min.Condition traps daily for a minimum of 10 minutes prior to use.7.3.1

Analyze the aqueous performance standard (Section 6.7.2) according to the purgeand trap procedure in Section 10. Compute the area at the primary m/z (Table4) for each compound. Compare these areas to those obtained by injecting 1 µLof the methanolic standard (Section 6.7.3) to determine compound recovery. Therecovery shall be greater than 20% for the water soluble compounds, and 60-110%for all other compounds. This recovery is demonstrated initially for each purgeand trap GC/MS system. The test is repeated only if the purge and trap orGC/MS systems are modified in any way that might result in a change inrecovery.

Demonstrate that 100 ng toluene (or toluene-d8) produces an area at m/z 91 (or99) approx one-tenth that required to exceed the linear range of the system. Theexact value must be determined by experience for each instrument. It is used tomatch the calibration range of the instrument to the analytical range and detectionlimits required.

7.3.2

7.4

Calibration by isotope dilution—the isotope dilution approach is used for the purgeableorganic compounds when appropriate labeled compounds are available and wheninterferences do not preclude the analysis. If labeled compounds are not available, orinterferences are present, internal standard methods (Section 7.5 or 7.6) are used. Acalibration curve encompassing the concentration range of interest is prepared for eachcompound determined. The relative response (RR) vs concentration (µg/L) is plotted orcomputed using a linear regression. An example of a calibration curve for toluene usingtoluene-d8 is given in Figure 5. Also shown are the ±10% error limits (dotted lines).Relative response is determined according to the procedures described below. Aminimum of five data points are required for calibration (Section 7.4.4).7.4.1

The relative response (RR) of pollutant to labeled compound is determined fromisotope ratio values calculated from acquired data. Three isotope ratios are usedin this process:

Rx = the isotope ratio measured in the pure pollutant (Figure 6A).Ry = the isotope ratio of pure labeled compound (Figure 6B).

Rm = the isotope ratio measured in the analytical mixture of the pollutant andlabeled compounds (Figure 6C).

The correct way to calculate RR is: RR = (Ry-Rm) (Rx+1)/(Rm-Rx) (Ry+1). If Rm isnot between 2Ry and 0.5Rx, the method does not apply and the sample isanalyzed by internal or external standard methods (Section 7.5 or 7.6).

7.4.2

In most cases, the retention times of the pollutant and labeled compound are thesame and isotope ratios (R's) can be calculated from the EICP areas, where: R =(area at m1/z)/(area at m2/z). If either of the areas is zero, it is assigned a valueof one in the calculations; that is, if: area of m1/z = 50721, and area of m2/z = 0,then R = 50721/1 = 50720. The m/z's are always selected such that Rx >Ry.When there is a difference in retention times (RT) between the pollutant andlabeled compounds, special precautions are required to determine the isotoperatios.

Rx, Ry, and Rm are defined as follows:Rx = [area m1/z (at RT1)]/1Ry = 1/[area m2/z (at RT2)]Rm = [area m1/z (at RT1)]/[area m2/z (at RT2)]

7.4.3

An example of the above calculations can be taken from the data plotted inFigure 6 for toluene and toluene-d8. For these data, Rx = 168920/1 = 168900, Ry= 1/60960 = 0.00001640, and Rm = 96868/82508 = 1.174. The RR for the abovedata is then calculated using the equation given in Section 7.4.1. For the example,RR = 1.174.NOTE:

7.4.4

Not all labeled compounds elute before their pollutant analogs.

To calibrate the analytical system by isotope dilution, analyze a 5 mL aliquot ofeach of the aqueous calibration standards (Section 6.7.1) spiked with anappropriate constant amount of the labeled compound spiking solution (Section6.6), using the purge and trap procedure in Section 10. Compute the RR at eachconcentration.

Linearity—if the ratio of relative response to concentration for any compound isconstant (less than 20% coefficient of variation) over the five-point calibrationrange, an averaged relative response/concentration ratio may be used for thatcompound; otherwise, the complete calibration curve for that compound shall beused over the five-point calibration range.

7.4.5

7.5

Calibration by internal standard—used when criteria for isotope dilution (Section 7.4)cannot be met. The method is applied to pollutants having no labeled analog and to thelabeled compounds. The internal standards used for volatiles analyses arebromochloromethane, 2-bromo-1-chloropropane, and 1,4-dichlorobutane. Concentrationsof the labeled compounds and pollutants without labeled analogs are computed relativeto the nearest eluted internal standard, as shown in Table 2.7.5.1

Response factors—calibration requires the determination of response factors (RF)which are defined by the following equation:

Equation 1

where:

As = the EICP area at the characteristic m/z for the compound in the daily standard.

Ais = the EICP area at the characteristic m/z for the internal standard.Cis = the concentration (µg/L) of the internal standard.

Cs = the concentration of the pollutant in the daily standard.

7.5.2

The response factor is determined at 10, 20, 50, 100, and 200 for thepollutants (optionally at five times these concentrations for gases and watersoluble pollutants—see Section 6.7), in a way analogous to that for calibration byisotope dilution (Section 7.4.4). As/Ais is plotted vs. Cs/Cis for each compoundin the standard (Cs) to produce a calibration curve.

7.5.3

Linearity—if the response factor (RF) for any compound is constant (less than 35%coefficient of variation) over the five-point calibration range, an averaged responsefactor may be used for that compound; otherwise, the complete calibration curvefor that compound shall be used over the five-point range.

7.6

Combined calibration—by adding the isotopically labeled compounds and internalstandards (Section 6.6) to the aqueous calibration standards (Section 6.7.1), a single setof analyses can be used to produce calibration curves for the isotope dilution and internalstandard methods. These curves are verified each shift (Section 11.5) by purging theaqueous performance standard (Section 6.7.2). Recalibration is required only if calibrationand on-going performance (Section 11.5) criteria cannot be met.

8.8.1

Quality Assurance/Quality Control

Each laboratory that uses this method is required to operate a formal quality assuranceprogram. The minimum requirements of this program consist of an initial demonstrationof laboratory capability, analysis of samples spiked with labeled compounds to evaluateand document data quality, and analysis of standards and blanks as tests of continuedperformance. Laboratory performance is compared to established performance criteriato determine if the results of analyses meet the performance characteristics of the method.8.1.1

The analyst shall make an initial demonstration of the ability to generateacceptable accuracy and precision with this method. This ability is established asdescribed in Section 8.2.

The analyst is permitted to modify this method to improve separations or lowerthe costs of measurements, provided all performance specifications are met. Eachtime a modification is made to the method, the analyst is required to repeat theprocedure in Section 8.2 to demonstrate method performance.

Analyses of blanks are required to demonstrate freedom from contamination andthat the compounds of interest and interfering compounds have not been carriedover from a previous analysis (Section 3). The procedures and criteria for analysisof a blank are described in Sections 8.5 and 11.7.

The laboratory shall spike all samples with labeled compounds to monitormethod performance. This test is described in Section 8.3. When results of thesespikes indicate atypical method performance for samples, the samples are dilutedto bring method performance within acceptable limits (Section 14.2).

The laboratory shall, on an on-going basis, demonstrate through the analysis ofthe aqueous performance standard (Section 6.7.2) that the analysis system is incontrol. This procedure is described in Sections 11.1 and 11.5.

The laboratory shall maintain records to define the quality of data that isgenerated. Development of accuracy statements is described in Sections 8.4 and11.5.2.

8.1.2

8.1.3

8.1.4

8.1.5

8.1.6

8.2

Initial precision and accuracy—to establish the ability to generate acceptable precisionand accuracy, the analyst shall perform the following operations:8.2.1

Analyze two sets of four 5 mL aliquots (eight aliquots total) of the aqueousperformance standard (Section 6.7.2) according to the method beginning in Section10.

Using results of the first set of four analyses in Section 8.2.1, compute the averagerecovery () in µg/L and the standard deviation of the recovery (s) in µg/L foreach compound, by isotope dilution for polluitants with a labeled analog, and byinternal standard for labeled compounds and pollutants with no labeled analog.For each compound, compare s and with the corresponding limits for initialprecision and accuracy found in Table 5. If s and for all compounds meet the8.2.2

8.2.3

acceptance criteria, system performance is acceptable and analysis of blanks andsamples may begin. If individual falls outside the range for accuracy, systemperformance is unacceptable for that compound. NOTE:

T he large number of compounds in Table 5 present a substantialprobability that one or more will fail one of the acceptance criteriawhen all compoulds are analyzed. To determine if the analyticalsystem is out of control, or if the failure can be attributed toprobability, proceed as follows:

8.2.4

Using the results of the second set of four analyses, compute s and for onlythose compounds which failed the test of the first set of four analyses (Section8.2.3). If these compounds now pass, system performance is acceptable for allcompounds and analysis of blanks and samples may begin. If, however, any ofthe same compounds fail again, the analysis system is not performing properlyfor the compound(s) in question. In this event, correct the problem and repeat theentire test (Section 8.2.1).

8.3

The laboratory shall spike all samples with labeled compounds to assess methodperformance on the sample matrix.8.3.18.3.28.3.3

Spike and analyze each sample according to the method beginning in Section 10.Compute the percent recovery (P) of the labeled compounds using the internalstandard method (Section 7.5).

Compare the percent recovery for each compound with the corresponding labeledcompound recovery limit in Table 5. If the recovery of any compound fallsoutside its warning limit, method performance is unacceptable for that compoundin that sample. Therefore, the sample matrix is complex and the sample is to bediluted and reanalyzed, per Section 14.2.

8.4

As part of the QA program for the laboratory, method accuracy for wastewater samplesshall be assessed and records shall be maintained. After the analysis of five wastewatersamples for which the labeled compounds pass the tests in Section 8.3.3, compute theaverage percent recovery () and the standard deviation of the percent recovery (sp) forthe labeled compounds only. Express the accuracy assessment as a percent recoveryinterval from -2sp to +2s = 10%, the accuracyp. For example, if = 90% and sp

interval is expressed as 70-110%. Update the accuracy assessment for each compoundon a regular basis (e.g., after each 5-10 new accuracy measurements).

Blanks—reagent water blanks are analyzed to demonstrate freedom from carry-over(Section 3) and contamination.8.5.1

The level at which the purge and trap system will carry greater than 5 µg/L ofa pollutant of interest (Table 1) into a succeeding blank shall be determined byanalyzing successively larger concentrations of these compounds. When a samplecontains this concentration or more, a blank shall be analyzed immediatelyfollowing this sample to demonstrate no carry-over at the 5 µg/L level.

8.5

8.5.2

With each sample lot (samples analyzed on the same eight hour shift), a blankshall be analyzed immediately after analysis of the aqueous performance standard(Section 11.1) to demonstrate freedom from contamination. If any of thecompounds of interest (Table 1) or any potentially interfering compound is foundin a blank at greater than 10 µg/L (assuming a response factor of one, relative tothe nearest eluted internal standard for compounds not listed in Table 1), analysisof samples is halted until the source of contamination is eliminated and a blankshows no evidence of contamination at this level.

8.6

The specifications contained in this method can be met if the apparatus used is calibratedproperly, then maintained in a calibrated state.

The standards used for calibration (Section 7), calibration verification (Section 11.5) andfor initial (Section 8.2) and on-going (Section 11.5) precision and accuracy should beidentical, so that the most precise results will be obtained. The GC/MS instrument inparticular will provide the most reproducible results if dedicated to the settings andconditions required for the analyses of volatiles by this method.

8.7

Depending on specific program requirements, field replicates may be collected todetermine the precision of the sampling technique, and spiked samples may be requiredto determine the accuracy of the analysis when internal or external standard methods areused.

Sample Collection, Preservation, and Handling

Grab samples are collected in glass containers having a total volume greater than 20 mL.Fill sample bottles so that no air bubbles pass through the sample as the bottle is filled.Seal each bottle so that no air bubbles are entrapped. Maintain the hermetic seal on thesample bottle until time of analysis.

Samples are maintained at 0-4°C from the time of collection until analysis. If the samplecontains residual chlorine, add sodium thiosulfate preservative (10 mg/40 mL) to theempty sample bottles just prior to shipment to the sample site. EPA Methods 330.4 and330.5 may be used for measurement of residual chlorine (Reference 8). If preservativehas been added, shake bottle vigorously for one minute immediately after filling.Experimental evidence indicates that some aromatic compounds, notably benzene,toluene, and ethyl benzene are susceptible to rapid biological degradation under certainenvironmental conditions. Refrigeration alone may not be adequate to preserve thesecompounds in wastewaters for more than seven days. For this reason, a separate sampleshould be collected, acidified, and analyzed when these aromatics are to be determined.Collect about 500 mL of sample in a clean container.

Adjust the pH of the sample to about 2 by adding HCl (1+1) while stirring. Check pHwith narrow range (1.4-2.8) pH paper. Fill a sample container as described in Section 9.1.If residual chlorine is present, add sodium thiosulfate to a separate sample container andfill as in Section 9.1.

9.9.1

9.2

9.3

9.4All samples shall be analyzed within 14 days of collection.

10.10.110.2

Purge, Trap, and GC/MS Analysis

Remove standards and samples from cold storage and bring to 20-25°C.

Adjust the purge gas flow rate to 40 ±4 mL/min. Attach the trap inlet to the purgingdevice and set the valve to the purge mode (Figure 3). Open the syringe valve locatedon the purging device sample introduction needle (Figure 1).

Remove the plunger from a 5 mL syringe and attach a closed syringe valve. Open thesample bottle and carefully pour the sample into the syringe barrel until it overflows.Replace the plunger and compress the sample. Open the syringe valve and vent anyresidual air while adjusting the sample volume to 5.0 mL. Because this process of takingan aliquot destroys the validity of the sample for future analysis, fill a second syringe atthis time to protect against possible loss of data. Add an appropriate amount of thelabeled compound spiking solution (Section 6.6) through the valve bore, then close thevalve.

Attach the syringe valve assembly to the syringe valve on the purging device. Open bothsyringe valves and inject the sample into the purging chamber.

Close both valves and purge the sample for 11.0 ± 0.1 minutes at 20-25°C.

After the 11-minute purge time, attach the trap to the chromatograph and set the purgeand trap apparatus to the desorb mode (Figure 4). Desorb the trapped compounds intothe GC column by heating the trap to 170-180°C while backflushing with carrier gas at20-60 mL/min. for four minutes. Start MS data acquisition upon start of the desorbcycle, and start the GC column temperature program three minutes later. Table 1summarizes the recommended operating conditions for the gas chromatograph. Includedin this table are retention times and detection limits that were achieved under theseconditions. Other columns may be used provided the requirements in Section 8 can bemet. If the priority pollutant gases produce GC peaks so broad that the precision andrecovery specifications (Section 8.2) cannot be met, the column may be cooled to ambientor sub-ambient temperatures to sharpen these peaks.

While analysis of the desorbed compounds proceeds, empty the purging chamber usingthe sample introduction syringe. Wash the chamber with two 5 mL portions of reagentwater. After the purging device has been emptied, allow the purge gas to vent throughthe chamber until the frit is dry, so that it is ready for the next sample.

After desorbing the sample for four minutes, recondition the trap by returning to thepurge mode. Wait 15 seconds, then close the syringe valve on the purging device tobegin gas flow through the trap. Maintain the trap temperature at 170-180°C. Afterapproximately seven minutes, turn off the trap heater and open the syringe valve to stopthe gas flow through the trap. When cool, the trap is ready for the next sample.

10.3

10.410.510.6

10.7

10.8

11.11.1

System Performance

At the beginning of each eight hour shift during which analyses are performed, systemcalibration and performance shall be verified for all pollutants and labeled compounds.For these tests, analysis of the aqueous performance standard (Section 6.7.2) shall be usedto verify all performance criteria. Adjustment and/or recalibration (per Section 7) shallbe performed until all performance criteria are met. Only after all performance criteriaare met may blanks and samples be analyzed.

BFB spectrum validity—the criteria in Table 3 shall be met.

Retention times—the absolute retention times of all compounds shall approximate thosegiven in Table 2.

GC resolution—the valley height between toluene and toluene-d8 (at m/z 91 and 99plotted on the same graph) shall be less than 10% of the taller of the two peaks.Calibration verification and on-going precision and accuracy—compute the concentrationof each polutant (Table 1) by isotope dilution (Section 7.4) for those compounds whichhave labeled analogs. Compute the concentration of each pollutant (Table 1) which hasno labeled analog by the internal standard method (Section 7.5). Compute theconcentration of the labeled compounds by the internal standard method. Theseconcentrations are computed based on the calibration data determined in Section 7.11.5.1For each pollutant and labeled compound, compare the concentration with the

corresponding limit for on-going accuracy in Table 5. If all compounds meet theacceptance criteria, system performance is acceptable and analysis of blanks andsamples may continue. If any individual value falls outside the range given,system performance is unacceptable for that compound.

NOTE:

The large number of compounds in Table 5 present a substantialprobability that one or more will fail the acceptance criteria whenall compounds are analyzed. To determine if the analytical systemis out of control, or if the failure may be attributed to probability,proceed as follows:

Analyze a second aliquot of the aqueous performance standard(Section 6.7.2).

Compute the concentration for only those compounds which failedthe first test (Section 11.5.1). If these compounds now pass, systemperformance is acceptable for all compounds and analyses ofblanks and samples may proceed. If, however, any of thecompounds fail again, the measurement system is not performingproperly for these compounds. In this event, locate and correct theproblem or recalibrate the system (Section 7), and repeat the entiretest (Section 11.1) for all compounds.

11.211.311.411.5

11.5.1.111.5.1.2

11.5.2Add results which pass the specification in Section 11.5.1.2 to initial (Section 8.2)

and previous on-going data. Update QC charts to form a graphic representation

of laboratory performance (Figure 7). Develop a statement of accuracy for eachpollutant and labeled compound by calculating the average percentage recovery(R) and the standard deviation of percent recovery (sr). Express the accuracy asa recovery interval from R-2sr to R+2s. For example, if R = 95% and srr = 5%, theaccuracy is 85-105%.

12.

Qualitative Determination—Accomplished by Comparison of Data from Analysis ofa Sample or Blank with Data from Analysis of the Shift Standard (Section 11.1).Identification Is Confirmed When Spectra and Retention Times Agree per the CriteriaBelow.

Labeled compounds and pollutants having no labeled analog

12.1.1The signals for all characteristic masses stored in the spectral library (Section

7.2.4) shall be present and shall maximize within the same two consecutive scans.12.1.2Either (1) the background corrected EICP areas, or (2) the corrected relative

intensities of the mass spectral peaks at the GC peak maximum shall agree withina factor of two (one-half to two times) for all masses stored in the library.12.1.3The retention time relative to the nearest eluted internal standard shall be within

±7 scans or ±20 seconds, whichever is greater.

12.2

Pollutants having a labeled analog

12.2.1The signals for all characteristic masses stored in the spectral library (Section

7.2.4) shall be present and shall maximize within the same two consecutive scans.12.2.2Either (1) the background corrected EICP areas, or (2) the corrected relative

intensities of the mass spectral peaks at the GC peak maximum shall agree withina factor of two for all masses stored in the spectral library.12.2.3The retention time difference between the pollutant and its labeled analog shall

agree within ±2 scans or ±6 seconds (whichever is greater) of this difference in theshift standard (Section 11.1).

12.3

Masses present in the experimental mass spectrum that are not present in the referencemass spectrum shall be accounted for by contaminant or background ions. If theexperimental mass spectrum is contaminated, an experienced spectrometrist (Section 1.4)is to determine the presence or absence of the compound.

12.1

13.13.1

Quantitative Determination

Isotope dilution—by adding a known amount of a labeled compound to every sampleprior to purging, correction for recovery of the pollutant can be made because thepollutant and its labeled analog exhibit the same effects upon purging, desorption, andgas chromatography. Relative response (RR) values for sample mixtures are used inconjunction with calibration curves described in Section 7.4 to determine concentrationsdirectly, so long as labeled compound spiking levels are constant. For the tolueneexample given in Figure 6 (Section 7.4.3), RR would be equal to 1.174. For this RR value,the toluene calibration curve given in Figure 5 indicates a concentration of 31.8 µg/L.Internal standard—calculate the concentration using the response factor determined fromcalibration data (Section 7.5) and the following equation:

Equation 2

13.2

where the terms are as defined in Section 7.5.1.

13.3

If the EICP area at the quantitation mass for any compound exceeds the calibration rangeof the system, the sample is diluted by successive factors of 10 and these dilutions areanalyzed until the area is within the calibration range.

Report results for all pollutants and labeled compounds (Table 1) found in all standards,blanks, and samples, in µg/L to three significant figures. Results for samples which havebeen diluted are reported at the least dilute level at which the area at the quantitationmass is within the calibration range (Section 13.3) and the labeled compound recoveryis within the normal range for the Method (Section 14.2).Analysis of Complex Samples

Untreated effluents and other samples frequently contain high levels (>1000 µg/L) of thecompounds of interest and of interfering compounds. Some samples will foamexcessively when purged; others will overload the trap/or GC column.

Dilute 0.5 mL of sample with 4.5 mL of reagent water and analyze this diluted samplewhen labeled compound recovery is outside the range given in Table 5. If the recoveryremains outside of the range for this diluted sample, the aqueous performance standardshall be analyzed (Section 11) and calibration verified (Section 11.5). If the recovery forthe labeled compound in the aqueous performance standard is outside the range givenin Table 5, the analytical system is out of control. In this case, the instrument shall berepaired, the performance specifications in Section 11 shall be met, and the analysis ofthe undiluted sample shall be repeated. If the recovery for the aqueous performancestandard is within the range given in Table 5, the method does not work on the samplebeing analyzed and the result may not be reported for regulatory compliance purposes.

13.4

14.14.1

14.2

14.3

Reverse search computer programs can misinterpret the spectrum of chromatographicallyunresolved pollutant and labeled compound pairs with overlapping spectra when a highlevel of the pollutant is present. Examine each chromatogram for peaks greater than theheight of the internal standard peaks. These peaks can obscure the compounds ofinterest.

Method Performance

The specifications for this method were taken from the inter-laboratory validation of EPAMethod 624 (Reference 9). Method 1624 has been shown to yield slightly betterperformance on treated effluents than Method 624. Additional method performance datacan be found in Reference 10.

15.15.1

References1.

“Performance Tests for the Evaluation of Computerized Gas Chromatography/MassSpectrometry Equipment and Laboratories,” USEPA, EMSL/Cincinnati, OH 45268,EPA-600/4-80-025 (April 1980).

Bellar, T.A. and Lichtenberg, J.J. “Journal American Water Works Association,” 66, 739(1974).

Bellar, T.A. and Lichtenberg, J.J. “Semi-automated Headspace Analysis of DrinkingWaters and Industrial Waters for Purgeable Volatile Organic Compounds,” inMeasurement of Organic Pollutants Water and Wastewater, C.E. VanHall, ed., AmericanSociety for Testing Materials, Philadelphia, PA, Special Technical Publication 686, (1978).“Working with Carcinogens,” DHEW, PHS, NIOSH, Publication 77-206 (1977).“OSHA Safety and Health Standards, General Industry,” 29 CFR Part 1910, OSHA 2206,(1976).

“Safety in Academic Chemistry Laboratories,” American Chemical Society Publication,Committee on Chemical Safety (1979).

“Handbook of Analytical Quality Control in Water and Wastewater Laboratories,”USEPA, EMSL/Cincinnati, OH 45268, EPA-4-79-019 (March 1979).

“Methods 330.4 and 330.5 for Total Residual Chlorine,” USEPA, EMSL/Cincinnati, OH45268, EPA-4-79-020 (March 1979).

“EPA Method Study 29 EPA Method 624-Purgeables,” EPA 600/4-84-054, NationalTechnical Information Service, PB84-209915, Springfield, Virginia 22161, June 1984.Colby, B.N., Beimer, R.G., Rushneck, D.R., and Telliard, W.A. “Isotope Dilution GasChromatography-Mass Spectrometry for the Determination of Priority Pollutants inIndustrial Effluents,” USEPA, Effluent Guidelines Division, Washington, DC 20460(1980).

2.3.

4.5.6.7.8.9.10.

Table 1—Volatile Organic Compounds Analyzed by Isotope Dilution GC/MS

Compound

Acetone..............Acrolein.............Acrylonitrile..........Benzene..............Bromodichloromethane..Bromoform...........Bromomethane........Carbon tetrachloride....Chlorobenzene........Chloroethane..........2-chloroethylvinyl ether..Chloroform...........Chloromethane........Dibromochloromethane..1,1-dichloroethane......1,2-dichloroethane......1,1-dichloroethene......Trans-1,2-dichloroethane.1,2-dichloropropane.....Cis-1,3-dichloropropene..Trans-1,3-dichloropropeneDiethyl ether..........P-dioxane............Ethylbenzene..........Methylene chloride.....Methyl ethyl ketone....1,1,2,2-tetrachloroethane.Tetrachlorethene.......Toluene..............1,1,1-trichloroethane....1,1,2-trichloroethane....Trichloroethene........Vinyl chloride.........

..............................................................................................................................................................................................................................................................................................................................................................................................................................................................................

Storet815523421034215340303210132104344133210234301343113457632106344183210534496345363450134546345413470434699815768158234371344238159534516344753401034506345113918039175

CASregistry67-64-1107-02-8107-13-171-43-275-27-475-25-274-83-956-23-5108-90-775-00-3110-75-867-66-174-87-3124-48-175-34-3107-06-275-35-4156-60-578-87-510061-01-510061-02-6

60-29-7123-91-1100-41-475-09-278-93-379-34-5127-18-4108-88-371-55-679-00-579-01-675-01-4

EPA-EGD

516 V002 V003 V004 V048 V047 V046 V006 V007 V016 V019 V023 V045 V051 V013 V010 V029 V030 V032 V. . . . . .033 V515 V527 V038 V044 V514 V015 V085 V086 V011 V014 V087 V088 V

NPDES. . . . . .001 V002 V003 V012 V005 V020 V006 V007 V009 V010 V011 V021 V008 V014 V015 V016 V026 V017 V. . . . . .. . . . . .. . . . . .. . . . . .019 V022 V. . . . . .023 V024 V025 V027 V028 V029 V031 V

Table 2—Gas Chromatography of Purgeable Organic Compounds by Isotope Dilution

GC/MSEGDNo.1

181245345246

Compound

Bromochloromethane (I.S.)Chloromethane-d3.......Chloromethane.........Bromomethane-d3.......

................................................................Ref EGDNo.....

181181245181

MeanMinimumretentionlevel2time (sec)(µg/L)

73010147501485024350

Table 2—Gas Chromatography of Purgeable Organic Compounds by Isotope Dilution

GC/MSEGDNo.1

Compound

Ref EGDNo.MeanMinimumretentionlevel2346Bromomethane..........................288Vinyl chloride-d3........................388Vinyl chloride...........................216Chloroethane-d5.........................316Chloroethane............................244Methylene chloride-d2.....................344Methylene chloride.......................616Acetone-d6.............................716Acetone................................002Acrolein...............................203Acrylonitrile-d3..........................303Acrylonitrile............................2291,1-dichloroethene-d2.....................3291,1-dichloroethene........................2131,1-dichloroethane-d3.....................3131,1-dichloroethane........................615Diethyl ether-d10........................715Diethyl ether............................230Trans-1,2-dichloroethene-d2................330Trans-1,2-dichloroethene...................614Methyl ethyl ketone-d3....................714Methyl ethyl ketone......................223Chloroform-13C1.........................323Chloroform.............................2101,2-dichloroethane-d4.....................3101,2-dichloroethane........................2111,1,1-trichloroethane-13C2..................3111,1,1-trichloroethane......................527p-dioxane..............................206Carbon tetrachloride-13C1..................306Carbon tetrachloride......................248Bromodichloromethane-13C1................348Bromodichloromethane....

................2321,2-dichloropropane-d6....................3321.2-dichloropropane.......................233Trans-1,3-dichloropropene-d4...............333Trans-1,3-dichloropropene..................287Trichloroethene-13C1......................387Trichloroethene..........................204Benzene-d6.............................304Benzene................

................251Chlorodibromemethane-13C1...............351Chlorodibromomethane....................214

1,1,2-trichloroethane-13C2

...

...............

time (sec)246246181301288304181378216386181512244517181554616565181566181606203612181696229696181778213786181804615820181821230821181840614848181861223861181901210910181989211999181100118210182061018182104524810451821123232113418211382331138182117228711871821200204121218212222511222182

1224(µg/L)

5050105050101050505050501010101050501010505010101010101010101010101010101010101010101010

Table 2—Gas Chromatography of Purgeable Organic Compounds by Isotope Dilution

GC/MSEGDNo.1

314019182247347215315285385183286386207307238338185

1

Compound

1,1,2-trichloroethane.....2-chloroethylvinyl ether...2-bromo-1-chloropropane (I.S.)Bromoform-13C1........Bromoform............1,1,2,2-tetrachloroethane-d21,1,2,2-tetrachloroethane..Tetrachloroethene-13C2...Tetrachloroethene.......1,4-dichlorobutale (int std)Toluene-d8............Toluene...............Chlorobenzene-d5.......Chlorobenzene.........Ethylbenzene-d10.......Ethylbenzene...........Bromofluorobenzene.....

..........

........................................................................

...........................................................................................................................................................................................Ref EGDNo..................

214182182182247183215183285183183286183207183238183

MeanMinimumretentionlevel2time (sec)(µg/L)

122410127810130610138610138610152510152510152810152810155510160310161910167910167910180210182010198510

Reference numbers beginning with 0, 1 or 5 indicate a pollutant quantified by the internal

standard method; reference numbers beginning with 2 or 6 indicate a labeled compoundquantified by the internal standard method; reference numbers beginning with 3 or 7indicate a pollutant quantified by isotope dilution.2

This is a minimum level at which the analytical system shall give recognizable mass spectra(background corrected) and acceptable calibration points. Column: 2.4 m (8 ft) x 2 mm i.d.glass, packed with one percent SP-1000 coated on 60/80 Carbopak B. Carrier gas: helium at40 mL/min. Temperature program: three minutes at 45°C, 8°C per minute to 240°C, hold at240°C for 15 minutes.NOTE:The specifications in this table were developed from data collected from three

wastewater laboratories.

Table 3—BFB Mass-Intensity Specifications

Mass

50759596173174175176177

Intensity required

15-40 percent of Mass 9530-60 percent of Mass 95base peak, 100 percent5-9 percent of Mass 95<2 percent of Mass 174>50 percent of Mass 955-9 percent of Mass 17495-101 percent of Mass 1745-9 percent of Mass 176

Table 4—Volatile Organic Compound Characteristic MassesLabeled Compound

Acetone..............Acrolein.............Acrylonitrile..........Benzene..............Bromodichloromethane..Bromoform...........Bromomethale.........Carbon tetrachloride....Chlorobenzene........Chloroethane..........2-chloroethylvinyl ether..Chloroform...........Chloromethane........Dibromochloromethane..1,1-dichloroethane......1,2-dichloroethane......1,1-dichloroethene......Trans-1,2-dichloroethene.1,2-dichloropropane.....Cis-1,3-dichloropropene..Trans-1,3-dichloropropeneDiethyl ether..........p-dioxane............Ethylbenzene..........Methylene chloride.....Methyl ethyl ketone....1,1,2,2-tetrachloroethane.Tetrachloroethene......Toluene..............1,1,1-trichloroethane....1,1,2-trichloroethane....Trichloroethene........Vinyl chloride.........

.......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

Analog

d6d2d3d613C13Cd313Cd5d5d713Cd313Cd3d4d2d2d6d4d4d10d8d10d2d3d213C2d8d313C213Cd3

Primary m/z’s

58/6456/5853/5678/8483/86173/17696/9947/48112/11764/71106/11385/8650/53129/13063/6662/6761/6561/6563/6775/7975/7974/8488/96106/11684/8872/7583/84166/17292/9997/10283/8495/13362/65

Table 5—Acceptance Criteria for Performance Tests

Acceptance criteria at 20 µg/L

Initial precision and

accuracySection 8.2.3s (µg/L)

Acetone.......................LabeledcompoundrecoverySections 8.3and 14.2

On-goingaccuracySection11.5R (µg/L)

Compound

X(µg/L)P (percent)

Note 1Table 5—Acceptance Criteria for Performance Tests

Acceptance criteria at 20 µg/L

Initial precision and

accuracySection 8.2.3s (µg/L)

Acrolein.............Acrylonitrile..........Benzene..............Bromodichloromethane..Bromoform...........Bromomethane........Carbon tetrachloride....Chlorobenzene........Chloroethane..........2-chloroethylvinyl ether..Chloroform...........Chloromethane........Dibromochloromethane..1,1-dichloroethane......1,2-dichloroethane......1,1-dichloroethene......Trans-1,2-dichloroethene.1,2-dichloropropane.....Cis-1,3-dichloropropene..Trans-1,3-dichloropropeneDiethyl ether..........P-dioxane............Ethyl benzene.........Methylene chloride.....Methyl ethyl ketone....1,1,2,2-tetrachloroethane.Tetrachloroethene......Toluene..............1,1,1-trichloroethane....

.....................................................................................................................................................................................................................................................................

LabeledcompoundrecoverySections 8.3and 14.2

On-goingaccuracySection11.5R (µg/L)

Compound

9.08.27.025.06.98.214.836.07.926.07.96.77.711.77.419.222.114.59.69.79.66.66.35.9

X(µg/L)P (percent)

Note 2Note 213.0-28.2ns-1966.5-31.5ns-1997.4-35.1ns-214d-54.3ns-41415.9-24.842-16514.2-29.6ns-2052.1-46.7ns-308d-69.8ns-55411.6-26.318-172d-55.5ns-41011.2-29.116-18511.4-31.423-19111.6-30.112-192d-49.8ns-31510.5-31.515-195d-46.8ns-343d-51.0ns-381d-40.2ns-284Note 1Note 115.6-28.5ns-203d-49.8ns-316Note 110.7-30.05-19915.1-28.531-18114.5-28.74-19310.5-33.412-200

4-33

4-346-36d-6112-304-35d-51d-798-30d-648-329-338-33d-528-34d-51d-56d-445-35d-507-3411-326-338-35

Table 5—Acceptance Criteria for Performance Tests

Acceptance criteria at 20 µg/L

Initial precision and

accuracySection 8.2.3s (µg/L)

1,1,2-trichloroethane.............TrichloroetheneVinyl chloride

Compound

LabeledcompoundrecoverySections 8.3and 14.2P (percent)

21-18435-196ns-452

On-goingaccuracySection11.5R (µg/L)

9-3212-34d-65

X(µg/L)

7.18.927.911.8-29.716.6-29.5d-58.5

d = detected; result must be greater than zero.

ns = no specification; limit would be below detection limit.

Note 1: Specifications not available for these compounds at time of release of this method.Note 2: Specifications not developed for these compounds; use Method 603.