A Comparison of Solid Phase Micro Extraction Devises, the Arrow Versus the Fiber, for the Determination of Algae Compounds in Water

Significance of the Topic

The odor compounds geosmin and 2-methylisoborneol (2-MIB) impart earthy off-flavors to drinking and recreational waters at concentrations below ten parts per trillion. Detecting these trace levels reliably is crucial for water quality monitoring, regulatory compliance, and consumer satisfaction.

Study Objectives and Overview

This application note evaluates two solid-phase microextraction (SPME) devices—the 120 µm DVB/Carbon WR/PDMS SPME arrow and the 2 cm 50/30 µm DVB/CAR/PDMS SPME fiber—for headspace sampling of geosmin and 2-MIB in water. The goal is to compare linearity, detection limits, precision, and accuracy under Standard Method 6040D conditions.

Methodology

Headspace SPME sampling was automated using the EST Analytical Flex Robotic Sampling Platform. Samples spiked with 5–100 ppt standards were salted with sodium chloride and incubated at 65 °C with agitation. Extraction proceeded for 30 minutes, followed by desorption in a GC injection port for 3 minutes. Analysis was performed by GC–MS in selected ion monitoring (SIM) mode.

Used Instrumentation

• EST Analytical Flex Robotic Sampling Platform with SPME option
• SPME devices: 120 µm DVB/Carbon WR/PDMS arrow and 2 cm 50/30 µm DVB/CAR/PDMS fiber
• Gas chromatograph with Rxi-5 Sil MS column (30 m × 0.25 mm × 0.25 µm)
• Mass spectrometer operated in SIM mode monitoring ions m/z 95, 107, 108, 112, 125, 126
• Carrier gas: helium; inlet temperature: 270 °C; oven program: 60 °C (2 min), ramp 8 °C/min to 200 °C, total run time ~21 min

Main Results and Discussion

Both SPME devices achieved excellent linearity (R² ≥ 0.997) over 5–100 ppt. Method detection limits (MDLs) ranged from 1.17 to 1.53 ppt. Precision (%RSD) at 5 ppt was below 7% and at 50 ppt below 4%. Recoveries of geosmin and 2-MIB fell between 99% and 116%. The arrow showed slightly lower MDLs and robust handling, while the fiber offered stronger analyte responses and marginally better sensitivity.

Benefits and Practical Applications

Automated headspace SPME simplifies sample preparation, reduces human error, and ensures reproducible results for trace odorant analysis. Laboratories can select the arrow for durability and lower detection limits or the fiber for enhanced signal intensity, adapting to throughput and performance needs.

Future Trends and Potential Applications

Advances may include novel SPME coatings tailored to specific odorants, integration of in-line sensors for real-time monitoring, miniaturized automated platforms for field deployment, and expansion to a broader suite of trace organic contaminants in environmental waters.

Conclusion

Both the SPME arrow and fiber meet Standard Method 6040D requirements for geosmin and 2-MIB in water. The arrow offers robustness and low MDLs; the fiber delivers stronger responses. Device choice should align with laboratory priorities for sensitivity, durability, and throughput.

References

• Standard Methods for the Examination of Water and Wastewater, Method 6040D: Constituent Concentration by Headspace Solid-Phase Microextraction, Part D.