Analysis of Trace Odorants in Drinking Water by Headspace-Solid Phase Microextraction-Gas Chromatography-Time of Flight Mass Spectrometry

Importance of the Topic

Trace odorants such as geosmin, 2-methylisoborneol (MIB) and methoxypyrazines impart musty or earthy aromas to drinking water at extremely low concentrations (ppt level). Because human sensory thresholds for these compounds can be as low as 10 ppt, reliable analytical methods are essential for monitoring and assuring water quality.

Objectives and Study Overview

The study adapts AWWA Method 6040D for automated headspace-SPME of only 10 mL samples and couples it to GC-TOFMS. Goals include demonstrating trace-level detection of targeted odorants, confirming analyte identity with full-scan mass spectra, and enabling identification of non-target compounds contributing to aroma profiles.

Methodology

Water standards (2.5–100 ppt) of IPMP, IBMP, MIB and geosmin were spiked with 10 ppt 2,4,6-TCA internal standard. Samples were salted out with NaCl to drive analytes into the headspace. A 2 cm DVB/Carboxen/PDMS SPME fiber extracted volatiles at 65 °C for 30 min under agitation. Desorption occurred at 260 °C for 3 min into a GC inlet in splitless mode.

Instrumentation Used

• Gerstel MPS2 autosampler with headspace-SPME option
• Agilent 6890 GC with Rxi-5ms column (20 m × 0.18 mm × 0.18 µm)
• LECO TruTOF HT GC-TOFMS, 70 eV EI, mass range 45–300 m/z at 20 spectra/s
• ChromaTOF software for deconvolution and library matching

Main Results and Discussion

The method achieved linear calibration from 2.5 to 100 ppt for all analytes with <10 % error versus certified concentrations. Full-scan TOFMS allowed deconvoluted spectra of 2-isopropyl-3-methoxypyrazine at 2.5 ppt with high library match scores. Expanded detection of non-target odorants was demonstrated.

Benefits and Practical Application of the Method

• Reduction of sample volume from 45 mL to 10 mL enables full automation.
• Full-scan TOFMS provides robust confirmation compared to SIM and screens for unexpected odorants.
• Suitable for routine QA/QC monitoring of drinking and bottled water.

Future Trends and Potential Applications

Further work could extend the workflow to detect packaging-derived volatiles in bottled water and integrate high-throughput data analysis. Advances in fiber coatings and faster mass analyzers may push detection limits even lower. The approach may also be applied to environmental monitoring of odor events.

Conclusion

The HS-SPME-GC-TOFMS adaptation of AWWA Method 6040D delivers sensitive, automated analysis of trace odorants in 10 mL water samples, combining low-ppt detection with comprehensive spectral confirmation and non-target screening capabilities.

References

1. American Water Works Association. Method 6040D.