Implementation of novel SPME Arrow for the trace-level analysis of taste and odor compounds in drinking water

Importance of the topic

Decaying algae blooms in drinking water release earthy and musty odor compounds such as 2-methylisoborneol (MIB) and geosmin. Although regulated only as secondary non-mandatory contaminants, these compounds drive consumer complaints and require analytical methods capable of detecting concentrations at or below their very low odor thresholds (low ng/L).

Objectives and overview of the study

This study evaluates a novel solid-phase microextraction Arrow (SPME Arrow) technique coupled with GC-MS to quantify MIB and geosmin at trace levels in drinking water. By implementing Standard Method 6040D with SPME Arrow and a Shimadzu GCMS-QP2020 NX system, the authors aimed to assess linearity, sensitivity, reproducibility, and sample throughput relative to conventional SPME fibers.

Methodology

• Sample preparation: 10 mL deionized water in 20 mL headspace vials with 3 g NaCl, spiked with MIB, geosmin, internal standard isobutyl-methoxypyrazine (IBMP, 10 ng/L), and surrogate isopropyl-methoxypyrazine (IPMP, 10 ng/L).
• Calibration range: 0.5 to 100 ng/L for MIB and geosmin; analyses in triplicate with blank runs between samples.
• SPME Arrow extraction: PDMS/DVB/Carboxen coating, equilibration at 65 °C for 10 min, extraction at 65 °C for 30 min, desorption at 250 °C for 10 min.

Instrumental setup

• GC-MS: Shimadzu GCMS-QP2020 NX with AOC-6000 autosampler.
• Column: SH-Rxi-624Sil MS (30 m × 0.25 mm × 1.40 μm), helium carrier gas, splitless injection (1 min), then split 20:1.
• Oven program: 50 °C to 195 °C at 40 °C/sec, then to 250 °C at 15 °C/sec, hold 2 min.
• MS conditions: Interface 250 °C; ion source 200 °C; detector voltage +0.5 kV; event time 0.3 sec; quantifier ions MIB (95, 93, 107, 108, 135), geosmin (112, 126), IBMP (124, 151, 94), IPMP (137, 152, 124).

Main results and discussion

• Calibration curves for both MIB and geosmin exhibited excellent linearity (R² = 0.99) across 0.5–100 ng/L.
• Limits of detection calculated at 3× signal-to-noise were 0.05 ng/L for both analytes, two orders of magnitude below their odor thresholds.
• Reproducibility at 10 ng/L (eight replicates) yielded 15% RSD for MIB and 12% RSD for geosmin; at the lowest level (0.5 ng/L), RSD was 0.2% for MIB and 5% for geosmin.
• Overall analysis time was approximately 30 minutes per sample by overlapping extraction and GC-MS runs.

Benefits and practical applications

• Enhanced sensitivity and robustness compared to conventional SPME fibers.
• Fast, automated workflow suitable for routine monitoring of taste and odor events in water utilities and environmental laboratories.
• Quantification well below odor thresholds enables rapid response and quality control.

Future trends and potential applications

• Integration with high-throughput automated platforms for real-time monitoring of taste and odor compounds.
• Adaptation of SPME Arrow for a broader range of volatile and semi-volatile contaminants in water, food, and environmental matrices.
• Development of portable GC-MS systems coupled with SPME Arrow for on-site field analysis.
• Design of novel SPME Arrow coatings to improve selectivity and extend application scope.

Conclusion

The SPME Arrow method combined with the Shimadzu GCMS-QP2020 NX provides a rapid, sensitive, and reproducible approach for trace-level analysis of MIB and geosmin in drinking water. Detection limits far below odor thresholds and robust precision support its adoption for effective taste and odor monitoring.

References

• Standard Method 6040D: Trace-level analysis of MIB and geosmin in drinking water.
• DiGregorio M., Owens A., Sandy A., Karbowski R., Marfil-Vega R., Lock N. Implementation of novel SPME Arrow for the trace-level analysis of taste and odor compounds in drinking water. Pittcon Conference & Expo Virtual Event; March 8–12, 2021.