EPA-NERL: 524.2:  VOCs in Water Using GCMS

  • Summary
  • Analytes
  • Revision
  • Data and Sites
Official Method Name
Measurement of Purgeable Organic Compounds in Water by Capillary Column Gas Chromatography/Mass Spectrometry
Current Revision
Revision 4.1, 1995
Media
WATER
Instrumentation
Gas Chromatography with Mass Spectrometry Detection
Method Subcategory
Organic
Method Source
  EPA-NERL
Citation
  EPA Method Guidance CD-ROM (includes MCAWW Methods, and most current EPA Methods)
Brief Method Summary
Inert gas is bubbled through a water sample to purge volatile organic compounds with low water solubility. Purged 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 into a capillary gas chromatography (GC) column. The concentrations of compounds from the trap are measured using a capillary column GC system equipped with a mass spectrometer (MS).
Scope and Application
This method determines purgeable volatile organic compounds (including some disinfection byproducts) in surface water, ground water, and drinking water in any stage of treatment.
Applicable Concentration Range
Approximate range is 0.02 - 200 ug/L for wide-bore thick-film capillary columns and 0.02 - 20 ug/L for narrow-bore thick-film capillary columns. Range is analyte and instrument dependent.
Interferences

(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.

Quality Control Requirements

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.

Sample Handling

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 4oC until analysis.

Maximum Holding Time
14 days.
Relative Cost
$201 to $400
Sample Preparation Methods
Dechlorination, pH adjustment.