Solid Phase Microextraction of Odors in Drinking Water, for Analysis by GC/MS

Importance of the Topic

Musty and earthy odors in drinking water, primarily caused by trace compounds such as geosmin, methylisoborneol (MIB) and methoxypyrazines, pose significant challenges for water utilities and beverage producers. Effective detection of these odorants at parts-per-trillion levels is critical for ensuring water quality, maintaining consumer confidence and complying with regulatory standards.

Objectives and Overview of the Study

The study presents a new solid phase microextraction (SPME) method, designated as AWWA method 6040D, for the selective headspace extraction and GC/MS analysis of trace odor compounds in drinking water. Key goals include achieving limits of detection down to 1–3 ppt, simplifying sample preparation compared with closed-loop stripping and purge-and-trap techniques, and validating linearity and reproducibility of the approach.

Methodology and Instrumentation

Sample extraction involves adding 25 mL of water sample and 6 g NaCl into a 40 mL vial with a stir bar, followed by heating to 65 °C and stirring. A 2 cm DVB/Carboxen/PDMS SPME fiber is exposed to the vial headspace for 30 min. Analytes are thermally desorbed in a 260 °C GC injection port.

Used Instrumentation

• SPME fiber: 2 cm StableFlex DVB/Carboxen/PDMS coating
• GC column: Equity-5 capillary, 30 m × 0.25 mm I.D. × 0.25 µm film
• GC/MS: 5973 MSD with helium carrier gas at 37 cm/s (1.0 mL/min constant flow)
• Oven program: 60 °C (2 min), ramp to 200 °C at 8 °C/min
• Injection: splitless for 1 min, then opened to 50 mL/min

Main Results and Discussion

The method achieved baseline resolution of geosmin, MIB, IPMP and IBMP with 2 ppt spiked standards, using 2,4,6-trichloroanisole (TCA) at 8 ppt as an internal standard. Selected-ion monitoring employed quantitation ions (e.g., 137 for IPMP, 124 for IBMP, 95 for MIB, 112 for geosmin, 197 for TCA) and secondary confirmation ions to ensure specificity. Calibration curves displayed excellent linearity with R² values ≥ 0.995 and y-intercepts close to zero, demonstrating reliable quantification at ultra-trace levels.

Benefits and Practical Applications

Compared to traditional solvent-based or purge methods, SPME offers a solventless, low-cost and straightforward workflow. It requires only small sample volumes (25 mL), reduces analyte dilution and enhances sensitivity. The technique is suitable for routine water quality monitoring in utilities, environmental laboratories and beverage production facilities.

Future Trends and Potential Applications

Ongoing advances in fiber coatings and automated SPME systems are expected to further lower detection limits and increase sample throughput. Integration with high-resolution mass spectrometry and real-time screening platforms may enable rapid on-site odor profiling and broader application to complex matrices beyond drinking water.

Conclusion

The AWWA 6040D SPME/GC-MS method provides a robust, sensitive and cost-effective solution for the analysis of trace odor compounds in drinking water. Its high linearity, minimal sample preparation and reliable performance support its adoption for routine quality control and regulatory compliance.

Reference

1. Eaton A, Nguyen D, Suhady L. Proceedings of the American Water Works Association Water Quality Conference, November 1999, M3-2.
2. Foster S, Nanci J, Owen C. Proceedings of the American Water Works Association Water Quality Conference, November 1999, M3-3.