The MultiFlex GC/Q-TOF as a Tool for the Investigation of Taste and Odour in Drinking Water

Significance of the Topic

Drinking water quality is governed by stringent regulations that control color, taste and odor to protect public health and ensure consumer acceptance. Occurrence of unusual off-odors, such as the so-called "pencil-like" smell, challenges routine monitoring techniques and demands a more investigative approach. Combining high-resolution mass spectrometry with olfactory detection bridges the gap between chemical identification and sensory perception, enabling precise pinpointing of trace contaminants responsible for undesirable odors.

Objectives and Study Overview

This study aimed to apply a MultiFlex GC/Q-TOF system equipped with an Olfactory Detection Port (ODP) to characterize odorous compounds in a drinking water sample suspected of contamination from new flooring materials. Key goals included:

• Profiling known taste and odor compounds by targeted analysis.
• Investigating unidentified aroma-active peaks using accurate mass data.
• Correlating olfactory descriptors with chemical identity.

Methodology and Instrumentation

Sample Extraction
An aliquot of 35 mL of the water sample was processed via automated in-tube solid-phase extraction (ITSP) with dichloromethane (DCM) as described in application note AS152.

GC/Q-TOF Analysis
The extract was analyzed on an Agilent 7890 GC coupled to a 7200 GC/Q-TOF with the following conditions:

• CIS4 inlet: 10 µL large-volume injection; temperature ramped from 10 °C to 240 °C.
• Column: HP-5MS, 30 m × 0.25 mm × 0.25 µm.
• Oven program: ramp to 300 °C.
• Mass spectrometer: Exact-mass EDR acquisition at 2 GHz; split 2:1 to MSD and ODP.

Used Instrumentation

• GERSTEL MultiPurpose Sampler (MPS) 2 XL Dual head
• GERSTEL Cooled Injection System (CIS) 4
• Agilent 7890 GC with 7200 GC/Q-TOF
• GERSTEL Olfactory Detection Port (ODP 3)

Main Results and Discussion

Initial single quadrupole EI data suggested a match to a C12H18O compound (pencil odour), but accurate mass measurement on the Q-TOF identified an empirical formula of C11H14O2 (M+ at m/z 178.0988 within 1 ppm). MS/MS fragmentation further confirmed the difference in structure. Olfactometric evaluation revealed multiple odor-active regions:

• A pencil/graphite aroma at two retention times: 13.8 min (matching the standard 2-tert-butyl-5-methyl-1,4-benzoquinone) and 21.7 min (novel C11H14O2 compound).
• A medicinal/perfume note from phenol and substituted phenols.
• Burnt or plastic odors correlated to adipates and potential antioxidant breakdown products.

Spiking experiments validated the presence of two distinct pencil-like compounds and highlighted the necessity of accurate mass to avoid misidentification by library hits alone.

Benefits and Practical Applications

The integration of high-resolution accurate mass data with olfactory detection enhances confidence in structural elucidation of unknown odorants. This approach enables water quality laboratories to:

• Rapidly pinpoint off-flavour sources.
• Differentiate isobaric or co-eluting contaminants.
• Support corrective actions in treatment and supply networks.

Future Trends and Applications

Emerging directions include coupling CI and MS/MS workflows to expand fragmentation libraries, developing real-time olfactometric monitoring for distribution networks, and miniaturizing GC/HRMS-ODP systems for on-site water quality assessments. Machine learning integration may further automate odor-compound correlations based on spectral and sensory data.

Conclusion

The MultiFlex GC/Q-TOF platform with an olfactory port offers a robust solution for comprehensive investigation of taste and odor issues in drinking water. By combining accurate mass measurements with sensory profiling, this method delivers unequivocal identification of both known and novel odorants.

References

• AS152: Optimisation and validation of an ITSP method for the determination of taste and odor compounds in water.