## 6200 VOLATILE ORGANIC COMPOUNDS*

6200 A. Introduction

1. Source and Significance

Many organic compounds have been detected in ground andsurface waters. While most groundwater contamination episodes are traceable to leaking underground fuel or solventstorage vessels, landfills, agriculture practices, and wastewater disposal, the most probable cause for contamination ofsome aquifers and surface waters has never been firmly established. Contamination may be due to past practices of on-site (leach field) disposal of domestic and industrial wastesor to illegal discharges. Organohalides, particularly the trihalomethanes, are present in most chlorinated water systems, especially those using surface waters as a source of supply. Toxicological studies on animal models have shown that some of these organics have the potential for teratogenesis or carcinogenesis in human beings. To minimize these healthrisks, sensitive detection and accurate and reproducible quantitation of organics is of paramount importance.

2. Selection of Method

Two capillary gas chromatographic methods for purgeable organic compounds are presented. The scope of analytes is detector-dependent. Method B is a gas chromatographic/mass spectrometric (GC/MS) technique. Method C combines GC withphotoionization detection (PID)/electrolytic conductivity detection (ELCD) in series. Methods B and C are applicable to a wide range of purgeable organics. Both methods can be applied to finished drinking water, drinking water in any stage of treatment, source water, or wastewater.

The methods presented are highly sophisticated micro-analytical procedures that should be used only by analysts experienced in chromatography and data evaluation and interpretation. While the methods are similar, they are not interchangeable from a regulatory point of view. 1,2

3. Scope

Table 6200:I lists the compounds that can be determined by these methods. All are determinable by both Methods B and C. Other compounds may be amenable to these methods.

4. Sampling and Storage

See Section 6010B.1

5. Quality Control

The quality control practices considered to be an integral part of each method are summarized in Table 6020:I. a. Initial quality control:1) Initial demonstration of capability—Conduct initial demonstration of capability study at least once, before analysis of any sample, by each analyst, to demonstrate proficiency with the method of choice. Include at least analysis of a reagent blank and four reagent blank samples fortified at a concentration between 10 times the minimum reporting level and the midpoint of the calibration curve. The blank should not contain any compound of interest at a concentration greater than minimum reporting level. Mean percent recovery for each compound calculated from the four fortified samples should be 80 to 120%, and the relative standard deviation (RSD) should be  20%.

2) Method detection level (MDL)—The MDL is a statisticaldetermination of the minimum concentration that can be measured by the method with a confidence level of 99% that theanalyte concentration is greater than zero. Determine MDL before any samples are analyzed, using the procedure described in Section 1030c or other appropriate procedure 3 as required for each matrix to be analyzed. For MDL calculation, start with a concentration about five times the estimated instrument detection level. Perform MDL determination as an iterative process. (Thevalues listed in Table 6200:III were generated using a concentration of 0.5 g/L.) Conduct MDL determination at least annually. Analyze samples for MDL determination over a 3- to 5-d period to generate a more realistic value.

3) Quality-control sample—Analyze an externally generated quality-control sample as a laboratory fortified blank at least quarterly or whenever new stock solutions are generated. Obtain this sample from sources external to the immediate laboratory, and use it to validate the laboratory’s standards both qualitativelyand quantitatively. Acceptance criteria are supplied by the manufacturer. If all criteria are not met, determine cause of error, and correct it before continuing.

4) Minimum quantitation level (MQL)—The MQL is the lowest level that can be quantified accurately. The MQL is defined as four times the MDL.

b. Calibration:1) Initial calibration—Perform initial calibration with a minimum of five concentrations of analytical calibration standards(CALs) for the compound(s) of interest. The lowest concentration should be at the working reporting level; the highest concentration should be at the upper end of the calibration range. Do not report values that are outside of the defined calibration range. For the calibration concentrations, there should be no more than one order of magnitude between concentrations.

Use any of the following calibration functions, as appropriate:response factor for internal standard calibration, calibration factor for external standard calibration, or calibration curve. Calibration curves may be linear through the origin, linear not through the origin, or quadratic through or not through the origin. Use the following recommended acceptance criteria for the various calibration functions. * Approved by Standard Methods Committee, 1997. Editorial revisions, 2011. Joint Task Group: 20th Edition—Melissa S. Dale (chair), Anthony Bucciferro, Melly L. Fabro, T.J. Richards, William A. Saner, Robert Slater.

1If using response factors or calibration factors, relative standard deviation (RSD) for each compound of interest should be less than 20%. If the RSD is not less than 20% for any compound of interest, then identify and correct source of lack of linearity before sample quantitation. When using response factors (i.e., for GC/MS analysis), check performance or sensitivity of theinstrument for the compound of interest against minimum acceptance values for the response factors. See specific analytical method for the acceptance criteria for the response factors for each compound.

For a linear regression, the correlation coefficient should be
0.994. Recalculate each calibration point compared to curve. Resulting values should be within  20%. If any of the recalculated values are not within  20%, identify and correct source of outlier(s) before sample quantitation.

Use initial calibration, with any of the above functions (response factor, calibration factor, or calibration curve) for quantitation of the analytes of interest in samples. Use continuing calibration, described in ¶ 2) below, only for checks on initialcalibration and not for sample quantitation. Perform initial calibration when instrument is set up and whenever continuing calibration criteria are not met.

2) Continuing calibration—Continuing calibration (CCAL) is the periodic analysis of a calibration standard used to verify that the instrument response has not changed significantly from the initial calibration. Perform continuing calibration every 10 samples for GC analysis, every 20 samples for GC/MS analysis, or every 12 h, whichever is more frequent.Perform continuing calibration with one or more of the concentrations of analytical standards in the initial calibration. Vary actual concentration of continuing calibration standard over calibration range, with a minimum concentration greater than two times the reporting limit. The acceptance criterion for continuing calibration is 70 to 130% recovery compared to the known or expected value of the calibration standard (at the analyst’s discretion, the acceptance criterion for the gases may be extended to 60 to 140% recovery). If the acceptancecriteria are not met, re-analyze continuing calibration standard or repeat initial calibration. When using response factors, check performance or sensitivity of instrument for analytes of interest against minimum acceptance values for response factors.

3) Closing standard—Finish all sample sets with a closing standard to demonstrate that performance was still acceptable for the last sample analyzed. Use acceptance criteria as for the CCAL.

c. Batch quality control: 1) Analytical day—An analytical day is defined as a 12-h analytical period.

2) Sample set (batch)—A sample set (batch) is defined as those samples extracted in an analytical day, not to exceed 20 samples.

3) Laboratory reagent blank (LRB)—A LRB is a blank sample consisting of all reagents that normally contact a samplewhen carried through the entire analytical procedure. Use reagent blank to determine contribution of reagents and preparative analytical steps to observed value. No compound of interest should be present in reagent blank at a level greater than the MQL. Include a minimum of one reagent blank with each sample set (batch). 4) Laboratory-fortified blank (LFB)—See ¶ b 2) above. N OTE : For this method, the LFB and CCAL are the same.

5) Internal standard (IS)—An internal standard is a compound of known concentration added to each standard and sample just before sample analysis. Because of the nature of purge and trap analysis, the IS is taken through the entire analytical process, just as is the surrogate standard [see ¶ 6) below]. However, the IS is used for quantitation, whereas the surrogate standard is used to monitor ongoing purge recovery. Use IS to monitor retention time, relative response, and concentration of analytes in each sample. When quantifying by the internal standard method,measure all compound responses relative to this standard. Internal standard area response should be in the range of  30% compared to the mean calibration curve area response. The IS compound should mimic the chromatographic conditions of the analytes of interest. The retention time of this compound should separate from all analytes of interest and elute in a representative area of the chromatogram. If a specific compound cannot be found to meet these criteria, use additional compounds to satisfy analytical needs.

6) Surrogate standard (SS)—A surrogate standard is a compound added to each standard and sample at a known concentration before extraction. Choose a compound(s) that is chemically similar to the analytes and that is unlikely to be found in environmental samples. Carry surrogate standard through entire sample extraction and analytical process to monitor extraction recovery for each sample. Surrogate recovery should remain reasonably constant over time. Recovery should not vary more than 30% from the known value. Refer to method of choice for specific surrogates.

7) Laboratory-fortified sample (LFS)—A LFS is an additional portion of a sample to which the analytes of interest have been added at a concentration at least two times the MRL or around the middle of the calibration range. Include a minimum of one LFS with each sample set (batch). Make LFSs at sufficient concentrations that sample background levels do not adversely affect recovery calculations. (If this is a known sample, adjust addition concentrations to be about five times background level). Base sample batch acceptance on results of CCALs and LFBs rather than on LFSs, because the matrix of the sample may interfere with method performance. Prepare fortifying solution for blanks and samples from a different primary mix than that used to develop working standard mix.

8) LFS duplicates—A LFS duplicate is a second LFS used to evaluate the precision of the method in a matrix sample. If sufficient sample volume is collected, fortify a large enough volume to yield two sample portions for analysis. If sufficient sample volume is not collected, use a second bottle of the same sample fortified to the same concentration as the first. Include a minimum of one LFS duplicate with each sample set (batch). Compare precision and bias to those listed in the method. Base sample batch acceptance on results of CCAL and LFB additions rather than LFS duplicates.

6. References

1. U.S. ENVIRONMENTAL PROTECTION A GENCY . 1987. National Primary

Drinking Water Regulations—synthetic organic chemicals; monitoring for unregulated contaminants; final rule. 40 CFR 141 & 142; Federal Register 52, No. 130. VOLATILE ORGANIC COMPOUNDS (6200)/Introduction

22. U.S. ENVIRONMENTAL PROTECTION A GENCY . 1986. Guidelines establishing test procedures for the analysis of pollutants under the Clean Water Act. 40 CFR Part 136; Federal Register 51, No. 125. 3. U.S. ENVIRONMENTAL PROTECTION A GENCY . 1995. Definition and procedure for the determination of the method detection limit, revision 1.11. 40 CFR Part 136, Appendix B.



## 6200 B. Purge and Trap Capillary-Column Gas Chromatographic/Mass Spectrometric Method

This method 1 is applicable to the determination of a wide range of purgeable organic compounds (see Table 6200:I). The methodcan be extended to include other volatile organic compounds, provided that all performance criteria are met. It should be used only by analysts experienced in the operation of GC/MS systems and in evaluation and interpretation of mass spectra.

1. General Discussion

a. Principle: Volatile organic compounds are transferred efficiently from the aqueous to the gaseous phase by bubbling an inert gas (e.g., helium) through a water sample contained in a specially designed purging chamber at ambient temperature. The vapor is swept through a sorbent trap that adsorbs the analytes of interest. After purging is complete, the trap is heated and back-flushed withthe same inert gas to desorb the compounds onto a gas chromatographic column. The gas chromatograph is temperature-programmed to separate the compounds. The detector is a mass spectrometer. See Section 6010C for discussion of gas chromatographic and mass spectrometric principles. T ABLE 6200:I. C OMPOUNDS D ETERMINABLE BY GAS C HROMATOGRAPHIC M ETHODS FOR PURGEABLE O RGANIC C OMPOUNDS

Analyte Chemical Abstract Services Registry Number Analyte Chemical Abstract Services Registry Number
Benzene 71-43-2 2,2-Dichloropropane 590-20-7 Bromobenzene* 108-86-1 1,1-Dichloropropene* 563-58-6 Bromochloromethane 74-97-5 cis -1,3-Dichloropropene* 10061-01-5 Bromodichloromethane 75-27-4 trans -1,3-Dichloropropene* 10061-02-6 Bromoform 75-25-2 Ethylbenzene* 100-41-4 Bromomethane 74-83-9 Hexachlorobutadiene* 87-68-3

n -Butylbenzene* 104-51-8 Isopropylbenzene* 98-82-8

sec -Butylbenzene* 135-98-8 p -Isopropyltoluene* 99-87-6

tert-Butylbenzene* 98-06-6 Methyl t-butyl ether* 1634-04-4 Carbon tetrachloride 56-23-5 Methylene chloride 75-09-2 Chlorobenzene* 108-90-7 Naphthalene* 91-20-3 Chloroethane 75-00-3 n -Propylbenzene* 103-65-1 Chloroform 67-66-3 Styrene* 100-42-5 Chloromethane 74-87-3 1,1,1,2-Tetrachloroethane 630-20-6 2-Chlorotoluene* 95-49-8 1,1,2,2-Tetrachloroethane 79-34-5 4-Chlorotoluene* 106-43-4 Tetrachloroethene* 127-18-4 Dibromochloromethane 124-48-1 Toluene* 108-88-3 1,2-Dibromo-3-chloropropane 96-12-8 1,2,3-Trichlorobenzene* 87-61-6 1,2-Dibromoethane 106-93-4 1,2,4-Trichlorobenzene* 120-82-1 Dibromomethane 74-95-3 1,1,1-Trichloroethane 71-55-6 1,2-Dichlorobenzene* 95-50-1 1,1,2-Trichloroethane 79-00-5 1,3-Dichlorobenzene* 541-73-1 Trichloroethene* 79-01-6 1,4-Dichlorobenzene* 106-46-7 Trichlorofluoromethane 75-69-4 Dichlorodifluoromethane 75-71-8 1,2,3-Trichloropropane 96-18-4 1,1-Dichloroethane 75-34-3 1,2,4-Trimethylbenzene* 95-63-6 1,2-Dichloroethane 107-06-2 1,3,5-Trimethylbenzene* 108-67-8 1,1-Dichloroethene* 75-35-4 Vinyl chloride* 75-01-4 cis -1,2-Dichloroethene* 156-59-4 o -Xylene* 95-47-6

trans -1,2-Dichloroethene* 156-60-5 m -Xylene* 108-38-3 1,2-Dichloropropane 78-87-5 p -Xylene* 106-42-3 1,3-Dichloropropane 142-28-9
* Compound can be determined using Method 6200C with PID only. VOLATILE ORGANIC COMPOUNDS (6200)/Purge & Trap Capillary-Column GC/MS Method

3b. Interferences: Impurities in the purge gas and organic compounds outgassing from the plumbing upstream of the trap account for most contamination problems. Demonstrate that the system is free from contamination under operational conditions by analyzing laboratory reagent blanks daily. (N OTE : Use blanks for monitoring only; corrections for blankvalues are unacceptable.) Avoid using non-TFE plastic tubing, non-TFE thread sealants, or flow controllers with rubber components in the purge and trap system. Ensure that the analytical area is not subject to contamination from laboratory solvents, particularly methylene chloride and methyl tert

butyl ether (MtBE).

Samples can be contaminated by diffusion of volatile organics (particularly fluorocarbons and methylene chloride) through the septum seal during shipment and storage. Use a field reagent blank prepared from reagent water and carried through the sampling, handling, and shipping procedures as a check on such contamination.

Contamination by carryover can occur whenever high-leveland low-level concentration samples are analyzed sequentially. To reduce carryover, rinse purging device and sample syringe with reagent water between samples. Follow analysis of an unusually high concentration sample with a LRB to check for carryover contamination. For samples containing large amounts of water-soluble materials, suspended solids,high boiling compounds, or high levels of volatile compounds, wash purging device with a detergent solution, rinse it with distilled water, and dry it in an oven at 105°C between analyses. The trap and other parts of the system also are subject to contamination; therefore, frequently bake and purge entire system.

c. Detection levels: Method detection levels (MDLs) are compound-dependent and vary with purging efficiency and instrument response. In a single laboratory using reagent water and known-addition concentrations of 0.5 g/L, observed MDLs were in the range of 0.025 to 0.450 g/L. The applicable calibration range of this method is compound- and instrument-dependent, but is approximately 0.2 to 200 g/L. Compounds that are inefficiently purged from water will not be detected when present at low concentrations, but they can be measured with acceptable bias and precision when presentat sufficient concentration. Determination of some geometrical isomers (e.g., xylenes) may be hampered by co-elution.

d. Safety: The toxicity or carcinogenicity of each analyte has not been precisely defined. Benzene, carbon tetrachloride,bis(1-chloroisopropyl)ether, 1,4-dichlorobenzene, 1,2-dichloroethane, hexachlorobutadiene, 1,1,2,2-tetrachloroethane,1,1,2-trichloroethane, chloroform, 1,2-dibromoethane, tetrachloroethene, trichloroethene, and vinyl chloride have been classified tentatively as known or suspect carcinogens. Handle pure standard materials and stock standard solutions of these compounds in a hood and wear a NIOSH/MESA-approved toxic gas respirator when handling high concentrations.

2. Apparatus

a. Purge and trap system: The purge and trap system consists of purging device, trap, and desorber. Several complete systems are available commercially.

1) Purging device, designed to accept 25-mL samples with a water column at least 5 cm deep. A smaller 5-mL purging device is acceptable if required method detection levels andperformance criteria are met. Keep gaseous headspace between water column and trap to a total volume of less than 15 mL. Pass purge gas through water column as finely divided bubbles with a diameter of less than 3 mm at the origin. Introduce purge gas no more than 5 mm from base of water column. The purging device illustrated in Figure 6200:1 meets these criteria.

Needle spargers may be used instead of the glass frit shown in Figure 6200:1; however, in either case, introduce purge gas at a point  5 mm from base of water column.

2) Trap, at least 25 cm long and with an inside diameter of at least 3 mm, packed with the following minimum lengths of adsorbents: 1.0 cm methyl silicone coated packing, 7.7 cm 2,6-diphenylene oxide polymer, 7.7 cm silica gel, and 7.7 cmcoconut charcoal. If analysis is not to be made for dichlorodifluoromethane, the charcoal may be eliminated and the polymer section lengthened to 15 cm. Alternative sorbents may be used provided that all quality control criteria are met. Various sorbent traps are available commercially*; ensure that trap keeps total purge gas volume and purge time constant (i.e., 40 mL/min for 11 min) and that performance will meet all quality control criteria. The minimum specifications for the trap are illustrated in Figure 6200:2.

Methyl silicone coated packing is recommended, but notmandatory. The packing protects the diphenylene oxide polymer adsorbent from aerosols, re-coating any active site that may develop during the heating process, and ensures that the polymer is fully enclosed within the heated zone of the trap, thus eliminating potential cold spots. Alternatively, silanized glass wool may be used as a spacer in the trap inlet.

* Tekmar VOCARB 4000 or equivalent. Figure 6200:1. Purging device. VOLATILE ORGANIC COMPOUNDS (6200)/Purge & Trap Capillary-Column GC/MS Method

4Before initial use, condition trap overnight following manufacturer’s instructions. Vent trap effluent to the room, not to analytical column. Before daily use, condition trap for 10 min with back-flushing. Optimally, vent trap to analytical columnduring daily conditioning; however, run column through temperature program before sample analysis.

b. Gas chromatograph (GC) †: Use a temperature-programmable GC, suitable for on-column injection. Deactivate all glass components (e.g., injector liners) with a silanizing agent.

c. Capillary GC columns: Use any capillary GC column that meets all performance criteria. Ensure that desorb flow rate iscompatible with the column of choice. Four examples of acceptable columns are listed below.

1) Column 1: 60-m-long  0.75-mm-ID VOCOL‡ wide-bore capillary column with 1.5-  m film thickness. 2) Column 2: 30-m-long  0.53-mm-ID DB-624§ mega-bore capillary column with 3-  m film thickness. 3) Column 3: 30-m-long  0.32-mm-ID DB-5§ capillary column with 1-  m film thickness. 4) Column 4: 30-m-long  0.25-mm-ID DB-624§ capillary column with 1.4-  m film thickness. d. Mass spectrometer, capable of scanning from 35 to 300 amu every 2 s or less, utilizing 70 eV (nominal) electron energy in the electron impact ionization mode, and producing a mass spectrum that meets all criteria in Table 6200:II when 25 ng or less of 4-bromofluorobenzene is introduced into GC. Toensure sufficient precision, the desired scan rate permits acquisition of at least five spectra while a sample component elutes from the GC.

e. Purge and trap—GC/MS interface: Use an open-split or direct-split interface, depending on which column is used. Alternatively, if the narrow-bore column (4) is used, a capillary concentrator preceding the GC may be necessary. This interface condenses desorbed materials onto an uncoatedfused silica pre-column and when flash-heated transfers compounds onto the capillary column. The uncoated section of column is cooled to

 150°C during desorption and heated to 250°C to transfer condensed materials.

f. Data system: To the mass spectrometer attach a computer that allows continuous acquisition and storage of all mass spectra obtained throughout the chromatographic program. Computer software should allow for a search of all acquired spectra for specific m/z (masses) and the plot of such m/z abundances versus time or scan number. This type of plot is an extracted ion current profile (EICP). Software also should allow the integration of the abundances in any EICP over a specified time or scan limit.

g. Syringes, 0.5-, 1.0-, 5-, and 25-mL glass hypodermic with detachable tip. 

h. Syringe valves, two-way, with detachable tip.  i. Microsyringes, 10-, 25-, and 100-  L with a 5-cm  0.15- mm-ID and 220 bevel needle.#

j. Bottles, 40-mL with TFE-lined screw cap.

3. Reagents

a. Reagent water, in which no interferent is observed at orabove the MDL of the constituents of interest. Prepare by passing tap water through a carbon filter bed containing about 0.5 kg activated carbon, by distillation, or by using a water purification system.**

b. Trap packing materials: 1) 2,6-Diphenylene oxide polymer, 60/80 mesh, chromatographic grade.

2) Methyl silicone packing, 3 OV-1. 3) Silica gel, 35/60 mesh. c. Methanol, purge-and-trap grade. d. Hydrochloric acid: HCl, 1  1. e. Vinyl chloride, 99.9% pure. f. Ascorbic acid

. g. Stock standard solutions: Prepare from pure standard materials or purchase as certified solutions. Prepare stock standard solutions in methanol using assayed liquids or gases as appropriate. C AUTION : Toxic substances. See 6200B.1 d

. † Gas chromatographic methods are extremely sensitive to the materials used. Mention of trade names by Standard Methods does not preclude the use of other existing or as-yet-undeveloped products that give demonstrably equivalent results. ‡ Supelco, Inc., or equivalent. § J&W, or equivalent.  Luerlok, or equivalent. # Hamilton #702, or equivalent. ** Millipore Super Q, or equivalent. T ABLE 6200:II. BFB KEY M/Z A BUNDANCE C RITERIA

Mass m/ z Abundance Criteria

50 15 to 40% of mass 95 75 30 to 60% of mass 95 95 Base peak, 100% relative abundance 96 5 to 9% of mass 95 173  2% of mass 174 174 50% of mass 95 175 5 to 9% of mass 174 176 95 to 101% of mass 174 177 5 to 9% of mass 176

Figure 6200:2. Trap packings and construction to include desorb capability. VOLATILE ORGANIC COMPOUNDS (6200)/Purge & Trap Capillary-Column GC/MS Method

5Place about 9.8 mL methanol in a 10-mL ground-glassstoppered volumetric flask. Let stand unstoppered for about 10 min or until all alcohol-wetted surfaces have dried. Weigh flask to nearest 0.1 mg.

Add assayed reference materials as follows: For liquids, using a 100-  L syringe or disposable capillary-tip glass pipet, immediately add two or more drops of assayed reference material to flask, then reweigh. Ensure that the drops fall directly into the alcohol without contacting flask neck. Forhalocarbon gases that boil below 30°C (bromomethane, chloroethane, chloromethane, dichlorofluoromethane, trichlorofluoromethane, vinyl chloride), attach a vinyl plastic†† tube to port of gas bottle containing reference material, with open end bubbling into a beaker of methanol showing flow through the tubing; insert needle of 5-mL valved gastight syringe into tube and pull gas into syringe slowly to 5.0-mL mark. Lower syringe needle to within 5 mm of methanol surface and slowly force gas onto surface. The gas will dissolve into the methanol and will be seen as a vortex as it dissolves into the solvent. Reweigh flask (difference is amount of gas dissolved into methanol), dilute to volume, stopper, and mix by invertingseveral times. Calculate concentration in micrograms per microliter from net gain in weight. When compound purity is assayed to be 96% or greater, calculate concentration of stockstandard from uncorrected weight. Preferably use commercially prepared stock standards at any concentration if they are certified by the manufacturer or an independent source. Transfer stock standard solution into a TFE-sealed screw-cap bottle. Store with minimum headspace at

 10 to

 20°C away from light.

h. Secondary dilution standards: Using stock standard solutions, prepare in methanol secondary dilution standards thatcontain the compounds of interest, either singly or mixed together. Prepare secondary dilution standards at concentrations that will permit aqueous calibration standards (¶ j below) to bracket working range of the analytical system. Store secondary dilution standards with minimal headspace in a freezer and check frequently for signs of evaporation (which would indicate need for regeneration). Always bring to room temperature before preparing calibration standards. Prepare standards fresh weekly for gases. Replace all other standards monthly, or sooner if comparison with check standards indicates a problem.

i. Internal standard/surrogate standard known addition: Prepare a solution containing fluorobenzene (internal standard) and 1,2-dichlorobenzene-d4 (surrogate) in methanol. Alternate inter

nal standard and surrogate compounds may be used, provided that they meet method criteria and do not interfere with any method analyte(s). Prepare secondary dilution standard at a concentration of 5  g/mL of each compound. Adding 5.0  L standard to 25.0 mL sample or calibration standard yields a concentration equivalent to 1.0 g/L. Alternate secondary standard concentrations can be used if addition volume is adjusted accordingly and all internal standard criteria are met. Add this mixture to each sample, standard, and blank.

j. Calibration standards: Prepare at least five concentration levels for each compound by adding appropriate amounts of secondary standard solution to reagent water and inverting water sample twice. Prepare one standard at a concentration near, but above, the MDL (i.e., 4  MDL for potable-water-type samples) or a level that defines the low end of the working range and theothers to correspond to the expected range of sample concentrations or to define the detector working range. Aqueous calibration standards can be stored up to 24 h if held in sealed vials withzero headspace. Otherwise, discard within 1 h. Alternatively, prepare calibration standards by injecting, with a solvent flush, an appropriate amount of a standard mix dilution and internal standard/ surrogate mix, directly into a 25-mL syringe filled with reagent water; immediately inject water standard into purge vessel.

4. Procedure

a. Operating conditions: Table 6200:III provides recommended operating conditions for the gas chromatograph and gives estimated retention times and MDLs that can be achieved under these conditions. An example of the separations obtained with the specified column is shown in Figure 6200:3. Otherchromatographic columns or conditions can be used if the quality control criteria are met.

b. GC/MS performance tests: At the beginning of each 12-h period during which analyses are to be performed, check GC/MS system by a performance test with BFB before any samples, blanks, or standards are analyzed. Performance tests require the following instrument parameters: Electron energy: 70 eV (nominal) Mass range: 35 to 300 amu Scan time: at least 5 scans/peak but not more than 2 s/scan

Inject 25 ng BFB directly on GC column. If direct injection is not easily performed, add 1  L 25-  g/mL BFB solution to 25 mL reagent water in syringe used for sample transfer to purge device and analyze as a sample. Obtain a background-corrected mass spectrum of BFB and confirm that all key m/z criteria in Table 6200:II are achieved. If all criteria are not achieved, re-tune mass spectrometer and repeat test until all criteria are met.

c. Calibration: Calibrate system as follows: 1) System setup—Condition trap initially overnight at 180°C by back-flushing with inert gas at 20 mL/min. Condition trapdaily for 10 min at manufacturer’s suggested temperature. Connect purge and trap system to GC using recommended temperature program and flow-rate conditions. Calibrate system by either the internal or the external standard technique.

2) Internal standard calibration technique—Select one or more internal standards similar in analytical behavior to thecompounds of interest. Fluorobenzene is a recommended internal standard compound. Demonstrate that measurement ofinternal standard is not affected by method or matrix interference. Because of such limitations, no one internal standard may be applicable to all samples. The compounds used as surrogates (e.g., 1,2-dichlorobenzene-d 4 ) for quality control also can be used successfully as internal standards. Prepare calibration standards at a minimum of five concentration levels for each compound as described in 6200B.3 j . Prepare a secondary dilution standard containing each of the internal standards (6200B.3 i ). Analyze each calibration standard according to procedure for samples, adding internal standard solution directly to syringe. Tabulate peak height or arearesponses against concentration for each compound and in†† Tygon, or equivalent. VOLATILE ORGANIC COMPOUNDS (6200)/Purge & Trap Capillary-Column GC/MS Method

6ternal standard, and calculate response factors (RF) for each compound in each calibration standard as follows:

RF  ( A s )( C is ) ( A is )( C s )

where:

A
s  response for compound to be measured, A is  response for internal standard, Cis  concentration for internal standard, and C

s  concentration of compound to be measured.
Calculate % RSD for the average RFs for each compound. Average RF can be used if RSD is less than 20%.

3) External standard calibration technique—Prepare standards as directed in 6200B.3 j . Analyze each calibration standard and tabulate peak area responses versus concentration. Prepare calibration curvefor each compound. Alternatively, if ratio of response to concentration (calibration factor) is a constant over the working range (  20% RSD), assume linearity through the origin and use average calibration factor in place of a calibration curve.

4) Calibration check—See 6200A.5 b 2). d. Sample analysis: Bring sample to ambient temperature. Remove plunger from 25-mL syringe and close attached valve. Open sample bottle and carefully pour sample into syringe barrel to just short of overflowing. Replace syringe plunger, invert syringe, and open valve. Vent any air and adjust sample volume to 25.0 mL, in duplicate if sufficient sample is available (once sample cap has been removed, sample cannot be stored, because of headspace). Add an appropriate amount of surrogate/internal standard through valve bore, and close valve. Attach to purge device, open valves, and inject sample into purge vessel. Close valves and purge sample for 11.0 min at ambient temperature at a flow rate of 40 mL/min (helium or nitrogen). If water vapor causes problems in the mass spectrometer, use a 3-min dry purge and/or a moisture control module. T ABLE 6200:III. PRIMARY Q UANTITATION I ON , RETENTION T IMES AND M ETHOD D ETECTION LEVELS

Analyte Retention Time min MDL


g/

L Primary

m/

z

Dichlorodifluoromethane 1.49 0.190 85 Chloromethane 1.71 0.150 50 Vinyl chloride 1.79 0.120 62 Bromomethane 2.16 0.220 94 Chloroethane 2.28 0.230 64 Trichlorofluoromethane 2.57 0.059 101 1,1-Dichloroethene 3.22 0.130 96 1,1,2-Trichloro-1,2,2-trifluoroethane 3.25 0.065 101 Methylene chloride 3.96 0.099 49
trans -1,2-Dichloroethene 4.40 0.200 96 Methyl t-butyl ether 4.45 0.450 73 1,1-Dichloroethane 5.14 0.047 63 cis -1,2-Dichloroethene 6.30 0.130 96 2,2-Dichloropropane 6.24 0.041 77 Bromochloromethane 6.77 0.032 128 Chloroform 7.00 0.126 83 1,1,1-Trichloroethane 7.24 0.043 97 1,1-Dichloropropene 7.67 0.040 75 Carbon tetrachloride 7.65 0.042 117 Benzene 8.07 0.036 78 1,2-Dichloroethane 8.14 0.055 62 Trichlorethene 9.44 0.045 95 1,2-Dichloropropane 9.85 0.053 63 Dibromomethane 10.07 0.035 93 Bromodichloromethane 10.47 0.112 83 cis -1,3-Dichloropropene 11.29 0.048 75 Toluene 11.81 0.047 91
trans -1,3-Dichloropropene 12.27 0.051 75 1,1,2-Trichloroethane 12.56 0.043 83 1,3-Dichloropropane 12.83 0.090 76 Tetrachloroethene 12.77 0.047 166 Dibromochloromethane 13.24 0.133 129 1,2-Dibromoethane 13.35 0.133 107 Chlorobenzene 14.21 0.052 112 1,1,1,2-Tetrachloroethane 14.37 0.048 131 Ethylbenzene 14.42 0.032 91
m,p -Xylene 14.63 0.038 91

o -Xylene 15.27 0.038 91 Styrene 15.30 0.031 104 Bromoform 15.60 0.131 173 Isopropylbenzene 15.90 0.074 105 Bromobenzene 16.34 0.140 156 1,1,2,2-Tetrachloroethane 16.41 0.066 83 1,2,3-Trichloropropane 16.44 0.072 75

n -Propylbenzene 16.57 0.260 91 2-Chlorotoluene 16.68 0.042 126 4-Chlorotoluene 16.86 0.040 126 1,3,5-Trimethylbenzene 16.88 0.035 105
tert-Butylbenzene 17.38 0.100 119

sec -Butylbenzene 17.46 0.025 105 1,2,4-Trimethylbenzene 17.74 0.046 105 4-Isopropyltoluene 17.99 0.037 119 1,3-Dichlorobenzene 17.89 0.045 146 1,4-Dichlorobenzene 18.04 0.033 146 1,2-Dichlorobenzene 18.64 0.031 146

n -Butylbenzene 18.65 0.028 91 Hexachlorobutadiene 21.69 0.033 225 1,2,4-Trichlorobenzene 21.34 0.043 180 Naphthalene 21.80 0.049 128 1,2,3-Trichlorobenzene 22.32 0.047 180

GC conditions: Column: J&W DB-624, 30 m, 0.25-mm ID, 1.4- m film; Temperature program: 35°C, 4 min; 4°C/min; 50°C, 0 min; 10°C/min; 175°C, 4 min. Figure 6200:3. GC/MS chromatogram. Column: J&W DB-624, 30 m, 0.25- mm ID, 1.4-  m film; temperature program: 35°C, 4 min; 4°C/min; 50°C, 0 min; 10°C/min; 175°C, 4 min. VOLATILE ORGANIC COMPOUNDS (6200)/Purge & Trap Capillary-Column GC/MS Method

7Desorb trapped materials onto head of chromatographic column at 180°C while back-flushing trap for 4 min with inert gas at a flow rate compatible with the column of choice, and begin GC temperature program.

Set system auto-drain to empty purge chamber while trap is being desorbed into GC, or alternatively, use sample syringe to empty vessel. Washing chamber with two 25-mL flushes of reagent water is useful if highly contaminated samples are being analyzed. Be sure all areas wetted during purging are also wetted during rinsing to maximize flushing.

Recondition trap by baking at conditioning temperature for 5 to 7 min. Let trap cool to ambient before introduction of next sample into purge vessel. When all sample compounds have been eluted from chromatographic column, end data acquisition and store data files. Use data system software to display full range mass spectra and appropriate extracted ion current profiles (EICP). If any ion abundances exceed system working range, dilute sample in second syringe with reagent water and analyze. N OTE : Take care with sample because compounds can be very volatile and can be lost if sample is reopened. Estimate amount of dilution needed and expel excess sample from second syringe, inject that portion intopurge vessel, and with a second syringe, add necessary reagent water to a total of 25.0 mL in purge vessel. 5. Calculation
When compounds have been identified, base quantitation onintegrated area abundance from the EICP of the primary characteristic m/z given in Table 6200:III. If sample produces an interference for the primary m/z , calculate a response factor or calibration curve using a secondary characteristic m/z , and use secondary m/z to quantitate. Report results in micrograms per liter. Report all quality control data with sample results.

6. Quality Control

See 6200A.5.

7. Precision and Bias

Typical single-laboratory precision and bias data are shown in Table 6200:IV.

8. Reference

1. U.S. ENVIRONMENTAL PROTECTION A GENCY . 1992. Methods for the

Determination of Organic Compounds in Finished Drinking Water and Raw Source Water. U.S. Environmental Protection Agency, Environmental Monitoring & Support Lab., Cincinnati, Ohio. T ABLE 6200:IV. S INGLE -LABORATORY B IAS AND P RECISION D ATA IN REAGENT WATER *

Analyte Recovery % Standard Deviation Relative Standard Deviation % Analyte Recovery % Standard Deviation Relative Standard Deviation %
Benzene 107 0.046 9 1,1-Dichloropropene 110 0.044 8 Bromobenzene 111 0.034 6 cis -1,3-Dichloropropene 99 0.044 9 Bromochloromethane 88 0.052 12 trans -1,3-Dichloropropene 101 0.038 7 Bromodichloromethane 104 0.036 7 Ethylbenzene 109 0.049 9 Bromoform 107 0.042 8 Hexachlorobutadiene 112 0.053 9 Bromomethane 89 0.049 11 Isopropylbenzene 112 0.044 8

n -Butylbenzene 115 0.048 8 4-Isopropyltoluene 117 0.046 8

sec -Butylbenzene 113 0.043 8 Methylene chloride 85 0.050 12

tert-Butylbenzene 116 0.057 10 Methyl t-butyl ether 81 0.017 11 Carbon tetrachloride 119 0.048 8 Naphthalene 121 0.068 11 Chlorobenzene 108 0.033 6 n -Propylbenzene 107 0.048 9 Chloroethane 115 0.073 13 Styrene 101 0.039 8 Chloroform 108 0.043 8 1,1,1,2-Tetrachloroethane 113 0.037 7 Chloromethane 74 0.036 10 1,1,2,2-Tetrachloroethane 104 0.053 10 2-Chlorotoluene 111 0.045 8 Tetrachloroethene 106 0.046 9 4-Chlorotoluene 112 0.049 9 Toluene 106 0.045 8 Dibromochloromethane 108 0.042 8 1,2,3-Trichlorobenzene 118 0.054 9 1,2-Dibromoethane 102 0.042 8 1,2,4-Trichlorobenzene 109 0.049 9 Dibromomethane 132 0.113 17 1,1,1-Trichloroethane 106 0.040 8 1,2-Dichlorobenzene 106 0.043 8 1,1,2-Trichloroethane 97 0.041 9 1,3-Dichlorobenzene 108 0.052 10 Trichloroethene 105 0.041 8 1,4-Dichlorobenzene 106 0.045 8 Trichlorofluoromethane 105 0.045 9 Dichlorodifluoromethane 80 0.058 15 1,2,3-Trichloropropane 104 0.034 61,1-Dichloroethane 109 0.049 9 1,1,2-Trichloro1,2,2-trifluoroethane 113 0.042 7 1,2-Dichloroethane 102 0.031 6 1,1-Dichloroethene 99 0.059 12 1,2,4-Trimethylbenzene 116 0.044 8 cis -1,2-Dichloroethene 103 0.062 12 1,3,5-Trimethylbenzene 110 0.051 9

trans -1,2-Dichloroethene 113 0.045 8 Vinyl chloride 85 0.037 9 1,2-Dichloropropane 129 0.064 10 m,p -Xylene 110 0.057 10 1,3-Dichloropropane 107 0.046 9 o -Xylene 106 0.044 8 2,2-Dichloropropane 106 0.049 9
* For all analytes, seven samples, each of 0.5  g/L concentration, were analyzed. VOLATILE ORGANIC COMPOUNDS (6200)/Purge & Trap Capillary-Column GC/MS Method

8

## 6200 C. Purge and Trap Capillary-Column Gas Chromatographic Method

This method 1 is applicable to the determination of purgeable halocarbons and aromatic organic compounds (Table 6200:I) in finished drinking water, raw source water, drinking water in any treatment stage, and wastewater.

1. General Discussion

a. Principle: See 6200B.1 a

. b. Interferences: See 6200B.1 b

. c. Detection levels: In a single laboratory using reagent water and known additions of 0.5  g/L, calculated method detection levels (MDLs) for these compounds were in the range of 0.01 to 0.05  g/L, depending on the compound. Some laboratories may not be able to achieve these detection levels because results depend on instrument sensitivity and matrix effects. Analysis of complex mixtures containing partially resolved compounds may be hampered by concentration differences larger than a factor of 10. This problem commonly occurs in analyses of finished drinking waters because of the relatively high trihalomethane content.

d. Safety: The toxicity or carcinogenicity of each reagent has not been defined precisely. Carbon tetrachloride, 1,2-dichloroethane,1,1,2,2-tetrachloroethane, 1,1,2-trichloroethane, chloroform, 1,2-dibromoethane, tetrachloroethene, trichloroethene, and vinyl chloride have been classified tentatively as known or suspected human ormammalian carcinogens. Prepare primary standards of these compounds in a hood and wear a NIOSH/MESA-approved toxic gas respirator when handling high concentrations.

2. Apparatus

a. Purge and trap system: The purge and trap system consists of three separate pieces of equipment: purging device, trap, and desorber. Several complete systems are commercially available.

1) Purging device—See 6200B.2 a 1). T ABLE 6200:V. RETENTION T IMES AND M ETHOD D ETECTION LEVELS

Analyte Retention Time min Method Detection Level

Analyte Retention Time min Method Detection Level Electrolytic Conductivity

Detector



g/

L Photoionization Detector



g/

L Electrolytic Conductivity

Detector



g/

L Photoionization Detector



g/

L
Dichlorodifluoromethane 6.22 0.037 — 1,3-Dichloropropane 31.18 0.020 — Chloromethane 7.09 0.041 — Dibromochloromethane 31.86 0.039 — Vinyl chloride 7.68 0.025 0.088 1,2-Dibromoethane 32.36 0.070 — Bromomethane 9.45 0.103 — Chlorobenzene 33.67 0.029 0.027 Chloroethane 9.76 0.025 — Ethylbenzene 33.89 — 0.028 Trichlorofluoromethane 11.04 0.042 — 1,1,1,2-Tetrachloroethane 33.91 0.020 — 1,1-Dichloroethene 13.59 0.018 0.035 m,p -Xylene 34.08 — 0.021 1,1,2-Trichloro-1,2,2- o -Xylene 35.44 — 0.024

trifluoroethane 13.07 0.047 — Styrene 35.67 — 0.027 Methylene chloride 15.83 0.068 — Isopropylbenzene 36.64 — 0.018 Methyl t-butyl ether 16.49 — 0.411 Bromoform 36.72 0.023 —

trans -1,2-Dichloroethene 16.78 0.015 0.015 1,1,2,2-Tetrachloroethane 37.43 0.034 — 1,1-Dichloroethane 18.49 0.015 — 1,2,3-Trichloropropane 37.88 0.048 — 2,2-Dichloropropane 20.27 0.220 — n -Propylbenzene 37.94 — 0.023 cis -1,2-Dichloroethene 20.54 0.012 0.032 Bromobenzene 37.98 0.026 0.026 Chloroform 21.04 0.017 — 1,3,5-Trimethylbenzene 38.44 — 0.019 Bromochloromethane 21.53 0.025 — 2-Chlorotoluene 38.48 0.017 0.017 1,1,1-Trichloroethane 22.14 0.014 — 4-Chlorotoluene 38.63 0.026 0.028 1,1-Dichloropropene 22.57 0.019 0.008 1,2,4-Trimethylbenzene 39.61 — 0.030 Carbon tetrachloride 22.80 0.022 — tert-Butylbenzene 39.76 — 0.018 Benzene 23.38 — 0.017 sec -Butylbenzene 40.34 — 0.018 1,2-Dichloroethane 23.62 0.074 — 4-Isopropyltoluene 40.80 — 0.019 Trichloroethene 25.30 0.012 0.014 1,3-Dichlorobenzene 41.01 0.017 0.028 1,2-Dichloropropane 25.92 0.021 — 1,4-Dichlorobenzene 41.40 0.059 0.061 Bromodichloromethane 26.63 0.040 — n -Butylbenzene 42.21 — 0.028 cis -1,3-Dichloropropene 28.38 0.067 0.041 1,2-Dichlorobenzene 42.62 0.023 0.031 Dibromomethane 28.40 0.057 — 1,2,4-Trichlorobenzene 48.21 0.019 0.028 Toluene 29.16 — 0.023 Hexachlorobutadiene 48.75 0.026 0.019

trans -1,3-Dichloropropene 30.00 0.029 0.046 Naphthalene 49.05 — 0.043 1,1,2-Trichloroethane 30.39 0.042 — 1,2,3-Trichlorobenzene 49.92 0.018 0.032 Tetrachloroethene 31.04 0.013 0.014
GC conditions: Column—Supelco VOCOL, 60 m, 0.75-mm ID, 1.5-  m film; Temperature program– 0°C, 8 min; 4°C/min; 185°C, 1.5 min. VOLATILE ORGANIC COMPOUNDS (6200)/Purge & Trap GC Method

9Figure 6200:4. PID chromatogram. GC conditions: Column: Supelco VOCOL, 60 m, 0.75-mm ID, 1.5-  m film; temperature program: 0° C, 8 min: 4° C/min; 185° C, 1.5 min.

Figure 6200:5. ELCD chromatogram. GC conditions: Column: Supelco VOCOL, 60 m, 0.75-mm ID, 1.5-  m film; temperature program: 0° C, 8 min; 4° C/min; 185° C, 1.5 min. VOLATILE ORGANIC COMPOUNDS (6200)/Purge & Trap GC Method

10T ABLE 6200:VI. S INGLE -LABORATORY B IAS AND P RECISION D ATA IN REAGENT WATER *
Photoionization Detector Electrolytic Conductivity Detector

Analyte Recovery % Standard Deviation Relative Standard Deviation % Recovery % Standard Deviation Relative Standard Deviation %

Benzene 70 0.006 2 — — — Bromobenzene — — — 89 0.008 2 Bromochloromethane — — — 83 0.008 2 Bromodichloromethane — — — 135 0.021 3 Bromoform — — — 81 0.007 2 Bromomethane — — — 73 0.033 9

n -Butylbenzene 63 0.009 3 — — —

sec -Butylbenzene 65 0.009 3 — — —

tert-Butylbenzene 72 0.006 2 — — — Carbon tetrachloride — — — 79 0.007 2 Chlorobenzene 70 0.009 2 97 0.009 2 Chloroethane — — — 64 0.008 2 Chloroform — — — 83 0.006 1 Chloromethane — — — 96 0.063 13 2-Chlorotoluene — — — 91 0.005 1 4-Chlorotoluene 73 0.009 2 81 0.008 2 Dibromochloromethane — — — 88 0.013 3 1,2-Dibromoethane — — — 139 0.022 3 Dibromomethane — — — 79 0.018 5 1,2-Dichlorobenzene 67 0.010 3 93 0.007 2 1,3-Dichlorobenzene 70 0.009 3 95 0.005 1 1,4-Dichlorobenzene 70 0.019 6 91 0.019 4 Dichlorodifluoromethane — — — 71 0.027 8 1,1-Dichloroethane — — — 82 0.005 1 1,2-Dichloroethane — — — 78 0.024 6 1,1-Dichloroethene 61 0.011 4 81 0.006 1 cis -1,2-Dichloroethene 61 0.010 3 76 0.004 1

trans -1,2-Dichloroethene 79 0.005 1 77 0.005 1 1,2-Dichloropropane — — — 85 0.007 2 1,3-Dichloropropane — — — 148 0.018 2 2,2-Dichloropropane — — — 74 0.045 12 1,1-Dichloropropene 54 0.003 1 74 0.006 2 cis -1,3-Dichloropropene 57 0.013 5 78 0.021 5

trans -1,3-Dichloropropene 63 0.015 5 78 0.009 2 Ethylbenzene 70 0.009 3 — — — Hexachlorobutadiene 55 0.006 2 76 0.008 2 Isopropylbenzene 67 0.006 2 — — — 4-Isopropyltoluene 65 0.006 2 — — — Methylene chloride — — — 83 0.022 5 Methyl t-butyl ether† 75 0.130 3 — — — Naphthalene 73 0.014 4 — — —

n -Propylbenzene 70 0.007 2 — — — Styrene 70 0.009 3 — — — 1,1,1,2-Tetrachloroethane — — — 83 0.001 0 1,1,2,2-Tetrachloroethane — — — 88 0.011 2 Tetrachloroethene 54 0.005 2 79 0.004 1 Toluene 69 0.007 2 — — — 1,2,3-Trichlorobenzene 72 0.010 3 84 0.006 1 1,2,4-Trichlorobenzene 70 0.009 3 94 0.006 1 1,1,1-Trichloroethane — — — 79 0.005 1 1,1,2-Trichloroethane — — — 118 0.014 2 Trichloroethene 57 0.004 2 80 0.004 1 Trichlorofluoromethane — — — 70 0.013 4 1,2,3-Trichloropropane — — — 87 0.015 3 1,1,2-Trichloro-1,2,2-trifluoroethane — — — 79 0.029 7 1,2,4-Trimethylbenzene 65 0.010 3 — — — 1,3,5-Trimethylbenzene 70 0.006 2 — — — Vinyl chloride 73 0.022 6 67 0.008 2
m,p -Xylene 73 0.007 2 — — —

o -Xylene 68 0.008 2 — — —
* For all analytes, seven samples, each at a concentration of 0.5  g/L (unless otherwise noted), were analyzed. † Sample concentration 5  g/L. VOLATILE ORGANIC COMPOUNDS (6200)/Purge & Trap GC Method

112) Trap—See 6200B.2 a 2). If only compounds boiling above 35°C are to be analyzed, both silica gel and charcoal can be eliminated and polymer increased to fill entire trap. Trap failure is characterized by a pressure drop above 21 kPa across trap during purging or by poor bromoform sensitivities.

3) Assembly—See Figures 6200:1 and 2. b. Gas chromatograph: See 6200B.2 b

. 1) Column—See 6200B.2 c

. 2) Electrolytic conductivity or microcoulometric detector

— Halogen-specific systems eliminate misidentifications due to non-organohalides that may be coextracted during purging.

3) Photoionization detector —A high-temperature detector equipped with a 10.2-eV (nominal) lamp.* Insert between analytical column and halide detector to analyze simultaneously for aromatic and unsaturated volatile organic compounds (see Table 6200:I).

c. Syringes, 5-mL glass hypodermic with detachable tip.† d. Other equipment: See 6200B.2g

– j

.

3. Reagents

See 6200B.3 a

–h

.

4. Procedure

a. Operating conditions: Table 6200:V summarizes recommended operating conditions for the gas chromatograph, estimated retention times, and method detection levels. Examples of separations obtained with the specified column are shown in Figures 6200:4 and 5.

b. Calibration: See 6200A.5 b . Use either internal or external calibration technique. If using internal standard technique, prepare a dilution standard as described in 6200B.3 i

.

c. Instrument performance: See 6200A.5. Ensure that all peaks in standard chromatograms are sharp and symmetrical. Correct anypeak tailing significantly in excess of that shown in method chromatograms. Tailing problems generally are traceable to active sites on the GC column or to detector operation. If only compounds eluting before chloroform give random responses or unusually wide peak widths, are poorly resolved, or are missing, the problemusually is traceable to the trap/desorber. If only brominated compounds show poor peak geometry or do not respond properly at lowconcentrations, replace trap. Excessive detector reactor temperatures also can cause low bromoform response. If negative peaks appear in the chromatogram, replace both ion-exchange column and electrolyte in detector. Check precision between replicate analyses. A properly operating system shows an average relative standard deviation of less than 10%. Poor precision generally is traceable to pneumatic leaks, especially around sample purger and detector reactor inlet and exit, electronic problems, or sampling and storageproblems. Monitor retention times for each compound using calibration standards and laboratory control standard. If individual retention times vary by more than 10% over an 8-h period or do not fall within 10% of an established norm, locate and correct source of retention data variance.

d. Sample analysis: See 6200B.5.

5. Calculation

Identify each organohalide in sample chromatogram by comparing retention time of suspect peak to retention times generated by calibration standards and laboratory control standard. Determine concentrations of individual compounds. If external standard calibration procedure is used, calculate concentration of compound being measured from peak response using calibration curve or calibration factor previously determined.

If internal standard calibration procedure is used, calculate concentration using response factor [RF, 6200B.4 c 2)] by the following equation:

Concentration,  g/L  A s  C is A is  RF

where:

A
s  response for compound to be measured, A is  response for internal standard, and Cis  concentration of internal standard. Report results in micrograms per liter without correction for recovery. Report quality control data with sample results.

6. Quality Control

See 6200A.5.

7. Precision and Bias

See Table 6200:VI.

8. Reference

1. U.S. ENVIRONMENTAL P ROTECTION A GENCY . 1991. Volatile organic

compounds in water by purge and trap capillary column gas chromatography with photoionization and electrolytic conductivity detectors in series. Method 502.2 in Methods for the Determination of Organic Compounds in Finished Drinking Water and Raw SourceWater. U.S. Environmental Protection Agency, Environmental Monitoring & Support Lab., Cincinnati, Ohio. * Tracor Model 703 or equivalent. † Luerlok, or equivalent. VOLATILE ORGANIC COMPOUNDS (6200)/Purge & Trap GC Method

12