Page 7: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Tetrachloroethylene
6.0 Analytical methods
The U.S. Environmental Protection Agency (U.S. EPA) currently has four approved analytical methods for the analysis of tetrachloroethylene in drinking water (U.S. EPA, 2002).
Method 502.2 Revision 2.1, which uses purge and trap capillary gas chromatography (GC) with photoionization detectors and electrolytic conductivity detectors in series, has a method detection limit (MDL) range of 0.02-0.05 μg/L. Method 524.2 Revision 4.1, which uses purge and trap capillary GC with mass spectrometry (MS) detection, has an MDL range of 0.05-0.14 μg/L. Method 524.3 Version 1.0 measures VOCs in drinking water. The method uses the GC-MS technique and has a detection limit of 0.036 µg/L for tetrachloroethylene. The advantages of the method include an optimization of the purge and trap parameters, an option for use of selected ion monitoring (SIM) and the use of solid acid preservatives (U.S. EPA, 2009). Method 551.1 Revision 1.0, employing liquid-liquid extraction and GC with electron capture detectors, has MDLs of 0.002 μg/L and 0.008 μg/L when methyl tertiary-butyl ether (MTBE) or pentane is used as the extraction solvent, respectively (U.S. EPA, 1995).
The current U.S. EPA practical quantitation level (PQL), based on the capability of laboratories to measure the concentration of tetrachloroethylene within reasonable limits of precision and accuracy, is 5 μg/L (U.S. EPA, 1991b). However, an assessment of the analytical data for tetrachloroethylene from performance evaluation and proficiency testing studies was recently conducted as part of the U.S. EPA's second 6-year review to re-evaluate PQLs (U.S. EPA, 2009). The U.S. EPA reported greater than 90% passing rates for laboratories analyzing samples, suggesting that the current PQL could be lower. This analysis included several studies with spiked concentrations below the current PQL. Applying a multiplier of 10 to the upper levels of the MDL of the three approved analytical methods (502.2, 524.2 and 551.1) resulted in a possible PQL range of 0.08-1.4 µg/L (U.S. EPA, 2009, 2010). The U.S. EPA's review indicated that the PQL could be lowered to approximately 0.5 µg/L (U.S. EPA, 2010).
In addition, three Standard Methods, SM 6200B, SM 6200C and SM 6232, can be used for the analysis of tetrachloroethylene in drinking water. Methods SM 6200B and SM 6200C are based on purge and trap capillary GC followed by MS detectors or photoionization detectors and electrolytic conductivity detectors in series, respectively. SM 6200B has an MDL of 0.047 μg/L, and SM 6200C has an MDL range of 0.013-0.014 μg/L. The minimum quantitation levels, defined as the lowest level that can be quantified accurately using these methods, are 0.188 μg/L and 0.056 μg/L for methods SM 6200B and SM 6200C, respectively (APHA et al., 2005). SM 6232 uses liquid-liquid extraction followed by GC with electron capture detectors. An MDL is not reported for this method due to its high dependency on the characteristics of the GC system used, solvent to water ratio and interferences present in the solvent (APHA et al., 2005).
ASTM International lists method D5790 for the analysis of tetrachloroethylene in drinking water. This method uses purge and trap capillary GC with MS detection (ASTM, 1999) and has an MDL of 0.25 μg/L (NEMI, 1995).
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