Determination of VOCs in Water by GC/MS after Headspace-Solid-Phase Microextraction (HS-SPME)

Significance of the Topic

Volatile aromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylenes (BTEX) are widespread environmental contaminants due to their use in industrial solvents and presence in petroleum products. Their moderate water solubility and toxicity make sensitive and reliable monitoring crucial for environmental safety, regulatory compliance, and public health protection. Optimizing sample preconcentration and detection protocols enhances trace-level analysis and supports quality control across water treatment and pollution assessment programs.

Objectives and Overview

The primary aim of the study was to compare a conventional 85 μm CAR/WR/PDMS SPME fiber with a 120 μm CAR/WR/PDMS SPME Arrow for the headspace extraction of BTEX in drinking water. Key goals included evaluating detection limits, repeatability, linearity of calibration, and practical applicability to real water samples. The work provides a direct comparison of sensitivity and method robustness between the two SPME geometries.

Methodology and Sample Preparation

Water samples (5 mL) were placed in 20 mL headspace vials along with 2 ±0.05 g NaCl to enhance analyte partitioning. The PAL RTC autosampler performed headspace-Solid Phase Microextraction (HS-SPME) with the chosen fiber or Arrow under identical conditions: 40 °C incubation, 1 000 rpm stirring, 5 min equilibration, 3 min extraction, and 4 min desorption.

Used Instrumentation

• PAL RTC autosampler with SPME headspace module
• Agilent 7890B gas chromatograph
• Agilent 5977B high-efficiency source mass spectrometer (GC/MSD)
• Agilent CP-Sil 5 CB capillary column (30 m × 0.25 mm, 1.0 μm film)

Main Results and Discussion

Calibration performance for all BTEX analytes showed high linearity (R² > 0.99) with both SPME devices; the Arrow consistently achieved slightly higher R² values (> 0.993) due to improved low-level response. Method detection limits (MDLs) with the Arrow ranged from 0.04 to 0.08 ppb, representing a roughly four- to fivefold improvement compared to the fiber (0.20 to 0.43 ppb). Repeatability assessments at 0.6 ppb (n=8) yielded relative standard deviations below 4% for the Arrow, outperforming the fiber (up to 25% RSD for some analytes).

The addition of sodium chloride demonstrated a salting-out effect, reducing analyte solubility and boosting headspace concentrations. Real-world application to three drinking water matrices confirmed non-detect or sub-LOQ results for BTEX, underscoring the method’s suitability for routine water quality screening.

Benefits and Practical Applications of the Method

• Enhanced sensitivity and lower detection limits support compliance with stringent regulatory thresholds.
• Improved precision and mechanical robustness of SPME Arrow reduce method variability and maintenance.
• Headspace extraction minimizes fiber contamination and extends device lifetime.
• Automated PAL RTC integration streamlines high-throughput environmental analysis.

Future Trends and Potential Applications

The promising performance of the SPME Arrow suggests broader adoption for ultra-trace analysis of other volatile organic compounds in various matrices (soil, air, beverages). Ongoing developments in stationary phases and device geometries may further push detection limits downward. Coupling with high-resolution mass spectrometry or rapid GC protocols could expand applications in forensic, food safety, and process monitoring sectors.

Conclusion

This comparative study demonstrates that the 120 μm CAR/WR/PDMS SPME Arrow offers significant advantages over the traditional 85 μm fiber for BTEX analysis in water, notably in sensitivity, linearity, and repeatability. The straightforward headspace-SPME protocol combined with GC/MS ensures reliable, high-throughput screening suitable for routine environmental and industrial laboratories.

Reference

Analysis of BTEX in Natural Water with SPME. Agilent Technologies Application Note, publication number SI-01251, September 2010.