EPA Method 502.2

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EPA Method 502.2:
Volatile Organic Compounds in Water by Purge and Trap Capillary Column Gas Chromatography with Photoionization and Electrolytic Conductivity Detectors in Series - Revision 2.1.

Inert gas is bubbled through a water sample to purge highly volatile organic compounds with low water solubility. Purged sample compounds are trapped in a tube containing suitable sorbent materials. When purging is complete, the sorbent tube is heated and backflushed with helium to desorb the trapped compounds onto a capillary gas chromatography (GC) column. The concentrations of compounds from the trap are measured using a capillary column GC system equipped with a photoionization detector (PID) and an electrolytic conductivity detector (ELCD) placed in series.

This method determines purgeable volatile organic compounds (including some disinfection by-products) in finished drinking water, raw source water, or drinking water in any treatment stage.

Methods for the Determination of Organic Compounds in Drinking Water - Supplement III (EPA/600/R-95-131)

(A) Contamination: Major contaminant sources are volatile materials in the laboratory and impurities in the inert purging gas and in the sorbent trap. The use of non-polytetrafluoroethylene (PTFE) plastic tubing, non-PTFE thread sealants, or flow controllers with rubber components in the purging device should be avoided since such materials out-gas organic compounds which will be concentrated in the trap during the purge operation. Analyses of laboratory reagent blanks provide information about the presence of contaminants. When potential interfering peaks are noted in the laboratory reagent blanks, the analyst should change the purge gas source and regenerate the molecular sieve purge gas filter. Subtracting blank values from sample results is not permitted. Also, when traps containing combinations of silica gel and coconut charcoal are used, residual water from previous analyses collects in the trap and can be randomly released into the analytical column. Therefore, as preventative maintenance, the trap should be reconditioned after each use.(B) Memory Interferences: Carryover may occur whenever high and low concentration samples are analyzed in sequence. For prevention, rinse sample syringe between samples with solvent. Also, unusually concentrated samples should be followed by the analysis of a solvent blank.

QC Requirements:
Initial demonstration of laboratory capability, followed by determination of surrogate compound recoveries in each sample and blank, monitoring internal standard peak area or height in each sample and blank, analysis of laboratory reagent blanks (LRBs), laboratory fortified matrices, laboratory fortified blanks (LFBs), and QC samples. A MDL for each analyte must also be determined.

Maximum Holding Time:
14 days.



Approximate range is 0.02 - 200 ug/L. Range is analyte and instrument dependent.

Data were generated in a single laboratory using 7 replicate analyses of reagent water fortified to 10 ug/L with each analyte. Recoveries were quantified using an internal standard method (Data from Column 1; 2-Bromo-1-chloropropane served as the internal standard). NOTE: Total trihalomethanes is a regulatory parameter for drinking water, representing the sum of trihalomethanes. See performance data for distinct trihalomethanes.

MDLs were determined using the standard deviation of replicate analyses of an analyte-fortified reagent water sample multiplied by the t-value for (# of samples - 1) degrees of freedom at the 99% confidence level. Detailed instructions for how MDLs are determined are found at 40 CFR part 136, Appendix B. Note: An MDL for 1,1,2-trichloromethane was determined on Column 2 using an external standard method. All other MDLs were determined on Column 1 using a 2-Bromo-1-chloropropane internal standard.

Revision Number:
Revision 2.1, 1995