6200 VOLATILE ORGANIC COMPOUNDS*

6200 A. Introduction

1. Source and Significance

Many organic compounds have been detected in ground and

surface waters. While most groundwater contamination episodes are traceable to leaking underground fuel or solvent

storage vessels, landfills, agriculture practices, and wastewater disposal, the most probable cause for contamination of

some 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 wastes

or 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 health

risks, 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 with

photoionization 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 statistical

determination of the minimum concentration that can be measured by the method with a confidence level of 99% that the

analyte concentration is greater than zero. Determine MDL before any samples are analyzed, using the procedure described in

Section 1030c or other appropriate procedure3 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. (The

values 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 qualitatively

and 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.

1
If 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 the

instrument 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 initial

calibration 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 acceptance

criteria 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 sample

when 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 ¶ b2) above. NOTE:

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 AGENCY. 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

2
2. U.S. ENVIRONMENTAL PROTECTION AGENCY. 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 AGENCY. 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 method1 is applicable to the determination of a wide range

of purgeable organic compounds (see Table 6200:I). The method

can 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 with

the 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.

TABLE 6200:I. COMPOUNDS DETERMINABLE BY GAS CHROMATOGRAPHIC METHODS FOR PURGEABLE ORGANIC COMPOUNDS

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

3
b. 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.

(NOTE: Use blanks for monitoring only; corrections for blank

values 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 tertbutyl 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-level

and 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 present

at 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 and

performance 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 cm

coconut 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 not

mandatory. 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

4
Before 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 column

during 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 is

compatible 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. To

ensure 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 uncoated

fused 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 or

above 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. CAUTION: Toxic substances. See 6200B.1d.

† 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.

TABLE 6200:II. BFB KEY M/Z ABUNDANCE CRITERIA

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

5
Place 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. For

halocarbon 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 inverting

several 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 stock

standard 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 that

contain 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 internal 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 the

others 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 with

zero 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. Other

chromatographic 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 trap

daily 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 the

compounds of interest. Fluorobenzene is a recommended internal standard compound. Demonstrate that measurement of

internal 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-d4) 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.3j. Prepare a

secondary dilution standard containing each of the internal

standards (6200B.3i). Analyze each calibration standard according to procedure for samples, adding internal standard

solution directly to syringe. Tabulate peak height or area

†† Tygon, or equivalent. responses against concentration for each compound and inVOLATILE ORGANIC COMPOUNDS (6200)/Purge & Trap Capillary-Column GC/MS Method

6
ternal standard, and calculate response factors (RF) for each

compound in each calibration standard as follows:

RF  (As)(Cis)

(Ais)(Cs)

where:

As  response for compound to be measured,

Ais  response for internal standard,

Cis  concentration for internal standard, and

Cs  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.3j. Analyze each calibration standard and tabulate

peak area responses versus concentration. Prepare calibration curve

for 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.5b2).

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.

TABLE 6200:III. PRIMARY QUANTITATION ION, RETENTION TIMES AND

METHOD DETECTION 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

7
Desorb 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. NOTE: 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 into

purge 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 on

integrated 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 AGENCY. 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.

TABLE 6200:IV. SINGLE-LABORATORY BIAS AND PRECISION DATA 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 6

1,1-Dichloroethane 109 0.049 9 1,1,2-Trichloro1,2,2-trifluoroethane113 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 method1 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.1a.

b. Interferences: See 6200B.1b.

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 or

mammalian 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.2a1).

TABLE 6200:V. RETENTION TIMES AND METHOD DETECTION 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

9
Figure 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

10
TABLE 6200:VI. SINGLE-LABORATORY BIAS AND PRECISION DATA 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

11
2) Trap—See 6200B.2a2). 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.2b.

1) Column—See 6200B.2c.

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.3a–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.5b. Use either internal or external

calibration technique. If using internal standard technique, prepare a

dilution standard as described in 6200B.3i.

c. Instrument performance: See 6200A.5. Ensure that all peaks

in standard chromatograms are sharp and symmetrical. Correct any

peak 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 problem

usually is traceable to the trap/desorber. If only brominated compounds show poor peak geometry or do not respond properly at low

concentrations, 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 storage

problems. 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.4c2)] by the

following equation:

Concentration, g/L  As  Cis

Ais  RF

where:

As  response for compound to be measured,

Ais  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 PROTECTION AGENCY. 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 Source

Water. 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