Page 7: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Toluene, Ethylbenzene and the Xylenes

6.0 Analytical methods

The U.S. Environmental Protection Agency (EPA) currently has three approved analytical methods (502.2 revision 2.1, 524.2 revision 4.1 and 524.3 version 1.0) for measuring toluene, ethylbenzene and xylenes (TEX) in drinking water (U.S. EPA, 2011). These methods are general analytical methods for the identification and measurement of purgeable VOCs. The methods use purge and trap procedures, followed by a capillary gas chromatography (GC) column to separate the analytes. After elution from the GC column, the analytes are identified by different detection techniques.

Method 502.2 revision 2.1 employs purge and trap capillary GC in combination with a photoionization detector. Method 524.2 revision 4.1 includes purge and trap of the samples and desorption of the trapped sample components into a capillary GC column interfaced to a mass spectrometer (MS). Both methods reported multiple MDL values, depending on the GC column and/or GC/MS interface used. Method 524.3 version 1.0 is an updated version of method 524.2. The advantages of this method include an optimization of the purge and trap parameters, an option for use of selected ion monitoring and the use of solid acid preservatives.

In addition, two equivalent standard methods, SM 6200B and SM 6200C, can be used for the analysis of toluene, ethylbenzene and xylenes in drinking water. These methods are based on purge and trap capillary GC followed by MS detection and a photoionization detector, respectively (APHA et al., 2012).

The analytical methods can explicitly identify the three xylene isomers if the isomers have sufficiently different retention times in the GC column. If two of the three xylene isomers cannot be resolved (separated) on the capillary column, the isomers are identified as an isomeric pair (U.S. EPA, 1995d). In this report, the term total xylene concentration refers to the total concentration of the three isomers.

The current U.S. EPA practical quantitation levels (PQLs) for toluene, ethylbenzene and total xylenes are set individually at 0.005 mg/L (5 µg/L) (U.S.EPA, 1991b).

6.1 Toluene

Method 502.2 revision 2.1 has an MDL in the range of 0.01–0.02 µg/L, depending on the GC column used. Method 524.2 revision 4.1 has an MDL in the range of 0.08–0.11 µg/L, depending on the GC column and GC/MS interface used (U.S. EPA, 1995d). Method 524.3 version 1.0 reported a detection limit of 0.024 µg/L (U.S. EPA, 2009).

Method SM 6200B has an MDL of 0.047 µg/L, and method SM 6200C has an MDL of 0.023 µg/L. The minimum quantitation levels, defined as the lowest levels that can be quantified accurately, are 0.188 µg/L and 0.092 µg/L for methods SM 6200B and SM 6200C, respectively (APHA et al., 2012).

6.2 Ethylbenzene

Method 502.2 revision 2.1 has an MDL in the range of 0.01–0.04 µg/L, depending on the GC column used. Depending on the GC column and GC/MS interface used, method 524.2 revision 4.1 allows MDL values in the range of 0.03–0.06 µg/L (U.S. EPA, 1995d). Method 524.3 version 1.0 has a detection limit of 0.01 µg/L (U.S. EPA, 2009).

Method SM 6200B has an MDL of 0.032 µg/L, and method SM 6200C has an MDL of 0.028 µg/L. The minimum quantitation levels, defined as the lowest levels that can be quantified accurately, are 0.128 µg/L and 0.112 µg/L for methods SM 6200B and SM 6200C, respectively (APHA et al., 2012).

6.3 Xylenes

Method 502.2 revision 2.1 has an MDL of 0.02 µg/L for o-xylene. The MDLs for both m- and p-xylene will be either 0.01 or 0.02 µg/L, depending on the GC column used for this method (U.S. EPA, 1995d). Depending on the GC column and GC/MS interface used, method 524.2 revision 4.1 allows MDL values in the range of 0.06–0.11 µg/L for o-xylene, 0.03–0.05 µg/L for m-xylene and 0.06–0.13 µg/L for p-xylene (U.S.EPA, 1995d). Method 524.3 version 1.0 reports a retention time of 11.3 minutes on the chromatographic column for o-xylene, and the method has a detection limit of 0.01 µg/L. The method defines m-xylene and p-xylene as an isomeric pair, with a detection limit of 0.02 µg/L (U.S. EPA, 2009).

Method SM 6200B reported a retention time of 15.27 minutes for o-xylene and has an MDL of 0.038 µg/L. The other two isomers have been defined as an isomeric pair, and the method reported an MDL of 0.038 µg/L. The minimum quantitation level for method SM 6200B is 0.152 µg/L. Method SM 6200C has an MDL of 0.024 µg/L for o-xylene and 0.021 µg/L for the m/p-isomeric pair. Method SM 6200C has minimum quantitation levels of 0.096 µg/L for o-xylene and 0.084 µg/L for the m/p-isomeric pair (APHA et al., 2012).

Table 2 summarizes the various analytical methods and their respective detection limits for each of the contaminants.

Table 2. Analytical methods for ethylbenzene, toluene and xylenes
Analytical method MDLs (µg/L)
Toluene Ethylbenzene o-Xylene m-Xylene p-Xylene
a U.S. EPA, (1995d)
b APHA, American Water Works Association and Water Environment Federation (2012)
502.2 rev. 2.1a 0.01–0.02 0.01–0.04 0.02 0.01–0.02 0.01–0.02
524.2 rev. 4.1a 0.08–0.11 0.03–0.06 0.06–0.11 0.03–0.05 0.06–0.13
524.3 ver. 1.0a 0.024 0.01 0.01 0.02 (isomeric pair)
SM 6200Bb 0.047 0.032 0.038 0.038 (isomeric pair)
SM 6200Cb 0.023 0.028 0.024 0.021 (isomeric pair)
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