Determination of 2-Methylisoborneol, Geosmin and 2,4,6-Trichloroanisole in Drinking Water by Dynamic Headspace Coupled to Selectable 1D/2D GC-MS with Simultaneous Olfactory Detection

Significance of the Topic

Earthy off-flavor compounds such as 2-methylisoborneol, geosmin and 2,4,6-trichloroanisole introduce musty odors in drinking water and require highly sensitive analytical methods at ng/L levels due to their low odor thresholds.

Objectives and Study Overview

This work presents a fully automated protocol combining dynamic headspace extraction with selectable one-dimensional/two-dimensional gas chromatography–mass spectrometry and simultaneous olfactory detection (DHS-1D/2D GC-O/MS) for trace analysis of off-flavor compounds in water samples.

Methodology and Instrumentation

• Sample preparation: 10 mL of water spiked, salted with 30% NaCl and incubated at 80 °C.
• Extraction: GERSTEL DHS module with Tenax TA adsorbent trap; optimized dry purge of 600 mL N₂ to remove water.
• Thermal desorption: Integrated TDU unit and PTV inlet for transfer to GC.
• Chromatography: Dual LTM GC system using DB-Wax (1D) and DB-5 (2D) columns with heart-cutting and fast temperature programming (100 °C/min).
• Detection: Agilent 7890 GC with 5975C MSD in SIM mode (m/z 95, 108, 112, 125, 195, 197) and an olfactory detection port.

Main Results and Discussion

• Heart-cutting and fast 2D GC significantly reduced background and sharpened analyte peaks.
• Signal-to-noise ratios improved by factors of 12 for MIB, 9 for geosmin and 3 for TCA compared to 1D GC-O/MS.
• Calibration was linear over 1–100 ng/L (r² > 0.9942); LODs ranged from 0.15 to 0.22 ng/L.
• Simultaneous MS and olfaction confirmed compound identities at concentrations as low as 1 ng/L.

Benefits and Practical Applications

The method offers solvent-free, highly sensitive extraction with minimal sample volume. Two-dimensional separation eliminates interferences and enhances quantitative reliability. Simultaneous olfactory detection provides additional confirmation of analyte identity.

Future Trends and Potential Applications

Anticipated developments include integration of high-throughput online monitoring, expansion to other trace volatiles in environmental and food matrices, and further system miniaturization for routine QA/QC workflows.

Conclusion

DHS-1D/2D GC-O/MS constitutes a robust, fully automated platform for ultratrace analysis of off-flavor compounds in drinking water, delivering sub-ng/L sensitivity, enhanced selectivity and sensory confirmation suitable for water quality management.

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