Comparison of Novel SPME Arrow with Traditional SPME Fiber for the Trace-level Analysis of Taste and Odor Compounds in Drinking Water

Importance of the Topic

Earthy and musty odors in drinking water are commonly attributed to trace levels of geosmin and 2-methylisoborneol. These compounds, produced by decaying algae, can lead to consumer complaints and trigger secondary maximum contaminant levels for taste and odor control. Sensitive, reliable, and high-throughput analytical tools are essential for utilities and environmental laboratories to monitor these compounds at concentrations well below their odor thresholds.

Objectives and Study Overview

This study evaluates a novel solid-phase microextraction Arrow device against a traditional SPME fiber for trace-level analysis of geosmin and 2-methylisoborneol in drinking water. Key goals include:

• Comparing calibration linearity and residual error between the two extraction techniques
• Determining method detection limits (MDLs) relative to odor thresholds
• Assessing reproducibility and sample throughput under automated conditions

Methodology

Water samples (10 mL) were combined with 3 g NaCl, spiked with geosmin and MIB standards (0.5–100 ng/L), an IBMP internal standard (10 ng/L), and an IPMP surrogate (10 ng/L). Headspace equilibration was performed at 65 °C for 10 min, followed by extraction at 65 °C for 30 min and thermal desorption at 250 °C for 10 min. Calibration curves covered 0.5 to 100 ng/L.

Instrumentation

• Gas chromatograph-mass spectrometer: Shimadzu GCMS-QP2020 NX
• Autosampler: Shimadzu AOC-6000 with overlapping extraction and analysis
• Extraction devices: PDMS/DVB/Carboxen SPME fiber (80 µm/1.1 mm OD) and SPME Arrow
• GC column: SH-Rxi-624Sil MS (30 m × 0.25 mm × 1.40 µm)
• GC oven program: 50 °C → 195 °C at 40 °C/s → 250 °C at 15 °C/s (2 min hold)
• Carrier gas: Helium at constant linear velocity (36.3 cm/s)
• MS conditions: EI ionization, interface 250 °C, ion source 200 °C, mass events for target ions (MIB: 93, 95, 107; geosmin: 112, 126; IBMP: 94, 124, 151; IPMP: 124, 137, 152)

Key Results and Discussion

Both extraction techniques exhibited excellent calibration linearity (R2 ≥ 0.99). The SPME Arrow delivered significantly lower MDLs, achieving 0.4 ng/L for MIB and 0.03 ng/L for geosmin, versus 7.5 ng/L and 0.08 ng/L by conventional fiber. These detection limits lie two orders of magnitude below odor thresholds (approx. 20 ng/L for MIB, 5 ng/L for geosmin). Reproducibility tests at 10 ng/L showed relative standard deviations of 3% (MIB) and 7% (geosmin) with the Arrow device. At the lowest calibration level (0.5 ng/L), RSDs were 27% and 22%, respectively. Chromatogram overlays confirmed reduced baseline noise and improved peak shape with the Arrow.

Benefits and Practical Applications

• Enhanced sensitivity enables early detection of taste and odor events well below regulatory thresholds.
• Improved robustness and lower residual sums of squares reduce quantitation uncertainty.
• Automated overlapping extraction and GC-MS analysis deliver 30 min sample throughput.
• Applicable to QA/QC and routine monitoring in water utilities and environmental laboratories.

Future Trends and Potential Uses

Advances may include coupling SPME Arrow with high-resolution mass spectrometry for non-targeted screening of additional odorous compounds. Miniaturized portable Arrow modules could support field testing. Further optimization of coating chemistries may broaden the range of volatile analytes while reducing extraction times. Integration into fully automated platforms promises greater throughput for large monitoring programs.

Conclusion

The SPME Arrow technique offers a clear advantage over traditional SPME fibers for trace-level analysis of geosmin and 2-methylisoborneol in drinking water. It delivers superior sensitivity, reproducibility, and throughput, supporting rapid and reliable taste and odor monitoring.

References

1. Owens A., Sandy A., Karbowski R., Marfil-Vega R., Lock N. Comparison of Novel SPME Arrow with Traditional SPME Fiber for the Trace-level Analysis of Taste and Odor Compounds in Drinking Water. Shimadzu Scientific Instruments, Inc., 2020.