EPA-NERL: 524.2:  VOCs in Water Using GCMS

(A) Contamination of samples with volatiles in the laboratory and impurities in the purge gas and sorbent trap: Use PTFE/Teflon or metal gas lines and plumbing (no out-gassing plastics), and analyze blanks to minimize risk of contamination.

(B) Contamination from sample carryover: Rinsing apparatus with water and purging equipment between analyses can minimize contamination.

(C) Contamination from methylene chloride (MeCl): When determining MeCl (a ubiquitous solvent) wear clothes that have not been exposed to MeCl fumes and use stainless steel or copper carrier gas and plumbing lines (MeCl permeates PTFE) to minimize contamination.

(D) Contamination of methanol: Ketones, methylene chloride, and other organic solvents often contaminate even high purity methanol.

Initial demonstration of laboratory capability followed by regular analyses of laboratory reagent blanks (LRBs), field reagent blanks (FRBs), and laboratory fortified blanks (LFBs). Initial demonstration of laboratory capability includes the analysis of four to seven replicates of an LFB containing each analyte of concern at a concentration in the range of 2 - 5 ug/L depending upon the calibration range of the instrumentation. Additional QC procedures are recommended. A method detection limit (MDL) must be determined for each analyte.

Dechlorinate samples using 25 mg of ascorbic acid per 40 mL of sample added to the sample bottle prior to collection. Additional amounts of ascorbic acid should be added per each 5 mg/L of residual chlorine. Sodium thiosulfate, at 3 mg per 40 mL of each water sample should be added for analytes such as vinyl chloride that are gases at room temperature or if analytes in Table 7 are not to be determined.

All samples should be collected in duplicate. Overfill all bottles, making sure to leave no bubbles or headspace. Adjust the pH of all samples to less than 2 at the time of collection, but after dechlorination with two drops of 1:1 HCl for each 40 mL of sample. When sampling for THM analysis only, acidification may be omitted if sodium thiosulfate is used to dechlorinate the sample. If sample foams vigorously after addition of HCl, discard the sample, collect a set of duplicate samples, but do not acidify them. Store samples at less than 4^oC until analysis.