In-Tube Extraction Dynamic Headspace (ITEX-DHS) sampling technique coupled to GC-MS for sensitive determination of odorants in water

Significance of the Topic

Water supplies can be affected by trace volatile compounds such as geosmin, isoborneol, 2-methyl-isoborneol and 2,4,6-trichloroanisole which impart earthy and musty odors at part-per-trillion levels. Accurate detection of these analytes is essential to safeguard consumer acceptability and comply with international water quality standards.

Study Objectives and Overview

This work evaluates the use of in-tube extraction dynamic headspace (ITEX-DHS) combined with gas chromatography–mass spectrometry (GC-MS) for sensitive quantification of four key odorants in water, targeting sub-ppt limits of detection within a fully automated workflow.

Methodology

ITEX-DHS employs a gas-tight syringe fitted with a Tenax GR:Carbosieve SIII micro trap to repeatedly sample headspace above 1 mL water aliquots in 20 mL vials. Key parameters—extraction strokes, trap temperature, flow rates, desorption temperature and speed—were optimized to balance sensitivity and throughput, achieving a total cycle time of 12 minutes without sample pretreatment.

Used Instrumentation

• Thermo Scientific TriPlus RSH autosampler with ITEX-DHS tool
• Thermo Scientific TRACE 1300 GC
• Thermo Scientific ISQ 7000 Single Quadrupole GC-MS
• TraceGOLD TG-5MS capillary column

Main Results and Discussion

The method delivered excellent linearity (r²≥0.999) over 1–100 ng/L (2-MIB, geosmin) and 5–100 ng/L (IB, TCA) with relative standard deviations below 11%. Method detection limits were below international thresholds of 10 ppt. Analysis of tap water from three sites confirmed all four analytes with repeatability better than 2.5% and qualifier/quantifier ion ratios within ±20%.

Benefits and Practical Applications

ITEX-DHS-GC-MS provides a solventless, high-capacity enrichment technique that is robust, easy to maintain and fully automatable, making it ideal for routine water quality monitoring and compliance testing.

Future Trends and Possibilities

Potential developments include extending ITEX-DHS to broader volatile organic compound panels, integrating high-resolution mass spectrometry, and deploying compact field-ready systems for on-site water analysis.

Conclusion

The ITEX-DHS approach coupled to GC-MS offers a rapid, sensitive and robust solution for trace odorant analysis in water, meeting sub-ppt detection demands and streamlining routine laboratory workflows.

References

1. ISO 17943: Water quality – Determination of volatile organic compounds in water – Method using headspace solid-phase micro-extraction (HS-SPME) followed by GC-MS, 2016.
2. GB 5749: Standards for drinking water quality, Chinese Ministry of Health, 2006.
3. Maher S. et al. An extensive review of extraction techniques and detection methods for geosmin in water. TrAC, 2019, 110, 233–248.
4. Helin A. et al. Solid phase microextraction Arrow for sampling volatile amines. J. Chrom. A, 2015, 1426, 56–63.
5. Laaks J. et al. In-Tube Extraction of VOCs from aqueous samples: an economical alternative to purge and trap. Anal. Chem., 2010, 82(18), 7641–7648.
6. Laaks J. et al. Optimization strategies of ITEX methods. Anal. Bioanal. Chem., 2015, 407, 6827–6838.
7. EPA 6040: Constituent concentration of gas extraction.