Benefits of a novel automated SPME technology for the detection of environmental pollutants at trace level in water

Importance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants known for their carcinogenic and mutagenic properties. Their presence in water at trace levels demands highly sensitive and reliable extraction and analysis techniques. Solid-phase microextraction (SPME) is a solvent-free, automatable sample preparation method widely used in environmental monitoring, but it has historically suffered from limited sorbent volume and fragility. The development of enhanced SPME devices can significantly improve detection limits, throughput, and robustness in routine water analysis.

Objectives and Study Overview

This study evaluates a novel automated SPME Arrow technology for the determination of the 16 EPA-regulated PAHs in water. The main aims are:

• To compare extraction efficiency of two PDMS SPME Arrow fibers (100 µm and 250 µm coatings) versus a classic 100 µm SPME fiber.
• To establish linearity, repeatability and method detection limits (MDLs) in the range of 1–500 ng/L.
• To assess the mechanical robustness and throughput potential under varying stirring speeds.

Methodology and Sample Preparation

Calibration standards for 16 PAHs were prepared at 0.1, 1.0 and 10 µg/L in methanol and diluted to 1–500 ng/L in ultrapure water. Fifteen-milliliter aliquots were transferred to 20 mL headspace vials. Direct immersion extraction was carried out at 35 °C for 60 min under stirring at 750 rpm (or 1500 rpm for select experiments). Calibration curves were constructed in triplicate to prevent analyte depletion.

Used Instrumentation

• Autosampler: Thermo Scientific TriPlus RSH with SPME Arrow tool, incubator and Heatex stirrer modules.
• Gas Chromatograph: Thermo Scientific Trace 1310 with instant-connect SSL injector and Arrow-compatible liner.
• Column: TG-5 SilMS, 30 m × 0.25 mm i.d. × 0.25 µm film.
• Mass Spectrometer: Thermo Scientific ISQ LT Single Quadrupole, electron ionization at 70 eV, operated in selected ion monitoring.

Main Results and Discussion

The enlarged sorption volume of the SPME Arrow fibers led to significantly higher peak areas for early-eluting (lower-boiling) PAHs compared to classic SPME. Linearity across 1–100 ppt showed R² values above 0.994 for both Arrow fibers. Repeatability (%RSD) ranged from 1.2 % to 9.2 %, and MDLs were between 0.27 and 1.67 ng/L. The 250 µm Arrow fiber offered slightly lower gains for heavier PAHs but still outperformed the classic fiber. Increasing stirring speed from 750 rpm to 1500 rpm further enhanced extraction of high-molecular-weight PAHs.

Benefits and Practical Applications

• Improved sensitivity and lower detection limits due to extended sorbent volume.
• Enhanced mechanical robustness under high-speed agitation.
• Fully automated workflow enabling high sample throughput and unattended operation.
• Elimination of solvent use and integration of extraction, desorption and injection steps.

Future Trends and Opportunities

Emerging directions for SPME Arrow include:

• Integration with high-resolution and tandem mass spectrometry for non-target screening.
• Development of novel sorbent chemistries for polar and ionic analytes.
• On-site and in-field sampling solutions for real-time water quality monitoring.
• Coupling with advanced data analytics and machine learning for pattern recognition of complex pollutant mixtures.

Conclusion

The SPME Arrow technology demonstrates clear advantages over classic SPME fibers in terms of extraction efficiency, sensitivity, and mechanical durability. Both 100 µm and 250 µm Arrow fibers deliver excellent linearity, repeatability and MDLs for trace PAH analysis in water, while supporting fully automated, high-throughput workflows.

References

1. US Government. Code of Federal Regulations, Primary Drinking Water Regulations: Maximum Contaminant Levels and Maximum Residual Disinfectant Levels. Title 40, Subpart G, 2002.
2. Directive 2013/39/EU of the European Parliament and of the Council, amending Directives 2000/60/EC and 2008/105/EC on priority substances in water policy.
3. Baltussen E., Sandra P., David F., Cramers C. Stir Bar Sorptive Extraction. Journal of Microcolumn Separations, 1999, 11, 737–747.
4. Kremser A., Jochmann M.A., Schmidt T.C. Enhanced Extraction of PAHs by Stir Bar Sorptive Extraction. Analytical and Bioanalytical Chemistry, 2016, 408(3), 943–952.
5. Cheng X., Forsythe J., Peterkin E. Factors Affecting SPME Analysis of PAHs in Urban Waterways. Water Research, 2013, 47, 2331–2345.