Analysis of 2-Methylisoborneol and Geosmin in Drinking Water by GC-MS and SPME Arrow

Significance of the Topic

2-Methylisoborneol and geosmin are trace-level odorants that impart earthy and musty tastes to drinking water, compromising consumer acceptance and safety. Their sensory thresholds are in the ng per liter range, making highly sensitive analytical methods essential for routine water quality monitoring and regulatory compliance.

Study Objectives and Overview

This study aimed to develop and validate a gas chromatography–mass spectrometry method using Solid Phase Microextraction Arrow for the quantitation of 2-MIB and geosmin in drinking water at concentrations down to 1 ng/L. Key goals included eliminating the traditional salting-out step, achieving low limits of quantitation, and demonstrating repeatability, linearity, and recovery in real water matrices.

Methodology

Standard solutions of 2-MIB and geosmin were prepared in methanol and spiked into Milli-Q water to yield calibration levels from 1 to 20 ng/L. Drinking water samples from two sources were analyzed by adding a small volume of methanol, followed by automated SPME Arrow extraction in an AOC-6000 Plus autosampler. Extraction conditions comprised incubation at 80 °C for 5 minutes with stirring at 1000 rpm, followed by 15 minutes of extraction and 2 minutes of desorption in splitless mode.

Instrumentation

• Autosampler: Shimadzu AOC-6000 Plus with Smart SPME Arrow 1.10 mm DVB/C-WR/PDMS
• Gas Chromatograph–Mass Spectrometer: Shimadzu GCMS-QP2020 NX
• Column: SH-I-5 Sil MS, 30 m × 0.25 mm ID × 0.25 μm film
• Carrier Gas: Helium at linear velocity 52.9 cm/s
• Injector Temperature: 250 °C; splitless injection
• Oven Program: 40 °C (2 min) ramp 10 °C/min to 120 °C, then 30 °C/min to 250 °C (5 min)
• MS Conditions: Ion source 200 °C, interface 250 °C, SIM mode targeting m/z 95 and 108 for 2-MIB, 112 and 125 for geosmin

Main Results and Discussion

The method achieved a limit of quantitation of 1 ng/L for both analytes with signal-to-noise ratios greater than 10. Five replicate analyses at 1 ng/L yielded area repeatability below 5 % RSD. Calibration curves were linear over the 1–20 ng/L range with R² values above 0.9998. Spike recovery experiments on two drinking water samples demonstrated recoveries between 70 % and 130 %, confirming method accuracy without employing salting-out.

Benefits and Practical Applications

• High sensitivity and precision at trace levels without salt addition simplify sample preparation.
• Durable SPME Arrow reduces consumable costs and maintenance downtime.
• Automated workflow enhances throughput for routine environmental and quality control laboratories.

Future Trends and Opportunities

Advances may include coupling SPME Arrow with high-resolution mass spectrometry for broader volatile profiling, miniaturized portable GC-MS systems for in situ water monitoring, and fully automated sample preparation platforms. Emerging materials for SPME coatings could further improve selectivity and lower detection limits for diverse odorants and pollutants.

Conclusion

The validated SPME Arrow–GC-MS method provides a robust, sensitive, and cost-effective approach for detecting 2-MIB and geosmin in drinking water at ng/L levels without salting-out. Its high repeatability, linearity, and recovery make it well suited for routine odorant monitoring in water quality control.

References

Huang et al , Kinetic and mechanistic investigation of geosmin and 2-methylisoborneol degradation using UV-assisted photoelectrochemical , Chemosphere 2022