Examination of Lower Molecular Weight PAHs in Drinking Water Using Agilent PDMS SPME Fibers

Significance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants comprising multiple fused aromatic rings. Due to their toxicity and regulatory limits in drinking water, sensitive analytical methods are essential for trace-level determination. Solid phase microextraction (SPME) streamlines sample preparation by minimizing solvent use and automating extraction, making it a powerful tool for environmental monitoring.

Objectives and Study Overview

This application brief evaluates the performance of three polydimethylsiloxane (PDMS) SPME fibers (7 µm, 30 µm, 100 µm) for the headspace extraction of lower molecular weight PAHs in drinking water. The study aims to identify the optimum fiber coating thickness and demonstrate reproducible quantitation using an automated PAL RTC rail system coupled to GC/MS.

Methodology

Sample preparation involved spiking 10 mL water vials with 25 µL of a 2.5 ppm PAH standard. Vials were vortexed, then placed on a PAL RTC rail system for headspace SPME. Extraction parameters included:

• Incubation: 5 min at 40 °C with 1,000 rpm stirring
• Fiber exposure: 10 min at 40 °C headspace
• Penetration depth/speed: 40 mm/20 mm/s into sample vial
• Desorption: 4 min in inlet, preconditioning as per run schedule

GC/MS analysis used an Agilent 7890B GC and 5977B GC/MSD under SIM mode. Key settings:

• Injection: splitless at 270 °C
• Oven program: 40 °C (2 min), ramp 20 °C/min to 260 °C, then 6 °C/min to 296 °C
• Column: 30 m × 0.25 mm, 0.25 µm DB-EUPAH
• Carrier flow: constant 1 mL/min
• MS: transfer line 280 °C, source 280 °C, quad 150 °C, SIM targeting characteristic ions for 16 PAHs

Instrumentation

• PAL RTC automated sample preparation rail
• SPME Arrow tool with PDMS fibers (7 µm, 30 µm, 100 µm)
• Agilent 7890B gas chromatograph
• Agilent 5977B mass selective detector
• 20 mL screw-cap headspace vials

Main Results and Discussion

Comparison of fiber coatings showed:

• 100 µm PDMS: highest response for low molecular weight PAHs (MW 60–275)
• 30 µm PDMS: suited for nonpolar semivolatiles (MW 80–500)
• 7 µm PDMS: effective for highest volatility compounds (MW 125–600)

Chromatograms confirmed sharper peaks and greater signal for target analytes using the 100 µm fiber. Reproducibility tests on three different 100 µm fibers yielded average relative standard deviations below 25% for all 16 PAHs, demonstrating robust quantitation.

Benefits and Practical Applications

The optimized SPME headspace workflow offers:

• Reduced solvent use and lower operational costs
• Automated, high-throughput sample preparation
• Enhanced sensitivity for regulatory compliance monitoring
• Versatility across environmental and industrial water testing

Future Trends and Opportunities

Advancements may include novel fiber coatings to extend the detectable range to ultra-volatile PAHs, integration with two-dimensional GC for complex mixtures, and onsite portable GC/SPME systems for rapid field screening.

Conclusion

This study demonstrates that a 100 µm PDMS SPME fiber combined with automated headspace extraction and GC/MS provides a sensitive, reproducible method for lower molecular weight PAHs in drinking water. The approach supports regulatory compliance and offers a scalable solution for routine environmental analysis.

References

• Godina L. Analysis of Low-Level PAHs in Drinking Water with an Agilent PAL3 equipped with SPME ARROW. Agilent Technologies Application Note 5994-0590EN, 2019.