Page 7: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Benzene

Part II. Science and Technical Considerations - Continued

6.0 Analytical methods

The United States Environmental Protection Agency (U.S. EPA) has approved two analytical methods, based on purge and trap gas chromatography, for the analysis of benzene in drinking water (U.S. EPA, 2002a). EPA Method 502.2 Revision 2.1, which employs purge and trap capillary gas chromatography with photoionization detectors and electrolytic conductivity detectors in series, has an MDL of 0.01 µg/L. EPA Method 524.2 Revision 4.1, which uses purge and trap capillary gas chromatography with mass spectrometry detection, has an MDL range of 0.03-0.04 µg/L. A detection limit range is cited, as multiple detection limits are possible as a result of variability in reagents, instrumentation, and/or laboratory analyst performance (U.S. EPA, 1995).

The current U.S. EPA practical quantitation limit (PQL) for benzene is set at 5 µg/L. This limit was previously considered the lowest level that could be reliably achieved within specified limits of accuracy and precision (U.S. EPA, 1985a). More recently, the U.S. EPA has identified benzene as a possible candidate for a PQL revision. Analysis of laboratory survey data indicated that a high percentage of laboratories were capable of measuring benzene concentrations in water at lower levels using common analytical methods (EPA Method 524.2) (U.S. EPA, 2003a). As a result, the U.S. EPA (2002b) has estimated a lower possible PQL of 0.4 µg/L.

Two equivalent standard methods, SM 6200B and SM 6200C, are based on purge and trap capillary gas chromatography followed by mass spectrometry detectors or photoionization detectors and electrolytic conductivity detectors in series, respectively. SM 6200B has an MDL of 0.036 µg/L, and SM 6200C has an MDL of 0.017 µg/L. The minimum quantitation levels, defined as the lowest level that can be quantified accurately, are 0.144 µg/L and 0.068 µg/L for methods SM 6200B and SM 6200C, respectively (APHA et al., 2005).

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