Method 6040D, Odors in Drinking Water, Using SPME on the Supelco SLB-5ms Capillary Column

A method for trace odor components, isopropyl-methoxypyrazine (IPMP), isobutyl-methoxypyrazine (IBMP), methylisoborneol (MIB), and geosmin in drinking water involving the use of solid phase microextraction (SPME) and the SLB-5ms capillary column using gas chromatography/mass spectrometry (GC–MS).

Musty odors in drinking water often are caused by chemical byproducts from the growth of blue-green algae. Some people can smell the odor analytes in drinking water at concentrations of 10 ppt or less. Thus, many water utility companies and beverage manufacturers must analyze for the presence of IPMP, IBMP, MIB, and geosmin at low concentrations. The use of head space SPME and the SLB-5ms column for low-level extraction and detection was used to determine the parts-per trillion (ppt) level of these compounds by Standard Method 6040D.

Figure 1

Results and Discussion

All four odor compounds were detected at ppt levels. Using SPME for extraction of the analytes proved to be fast, simple, and provided high sensitivity. Under consistent sampling conditions, drinking water analytes can be extracted with good precision over a range of concentrations. Inconsistent recoveries in SPME are often due to easily correctable factors such as variations in equilibration and extraction times, fiber position (both during extraction and desorption), or the condition of the fiber. SPME has utilized excellent precision and accuracy for a variety of quantitative applications, while reducing the time and expense of sample concentration in the analyses.

As a compliment to this low level extraction, the SLB-5ms provided adequate resolution and excellent peak shape for the analytes of interest. Symmetrical peak shape is critical for proper quantification, and can be essential for reproducible peak integration when working at ppt levels. In addition, low-level analyses require a column with minimal background. The SLB-5ms is a low bleed column designed for MS use, and for this application, column bleed did not interfere with the detection of the analytes in any way.

Conclusion

For low-level extraction and analysis of odor compounds in drinking water, this application provides an alternative to more time-consuming and costly methods, such as purge and trap (dynamic headspace), and closed loop-stripping, while demonstrating the usefulness of SPME in combination with the SLB-5ms. The DVB/carboxen/PDMS fiber provided the selectivity necessary for extraction of these compounds from the headspace of a drinking water matrix. The inertness and low bleed of the SLB-5ms column enabled subsequent low-level analysis by GC–MS.

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