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

Importance of the Topic

Trace levels of volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene and xylenes (BTEX) in water pose significant environmental and health risks. These compounds are common constituents of petroleum products and industrial solvents, exhibiting moderate water solubility and potential toxicity. Reliable detection at sub-ppb concentrations supports regulatory compliance, pollution monitoring and drinking water safety assessments.

Objectives and Overview of the Study

This work evaluates headspace solid-phase microextraction (HS-SPME) for quantitative analysis of BTEX in water. Two sampling devices—a conventional 85 µm Carboxen/PDMS SPME fiber and an enhanced 120 µm Carboxen/PDMS SPME Arrow—are compared in terms of sensitivity, linearity, repeatability and detection limits. The study employs a PAL RTC autosampler, an Agilent 7890B gas chromatograph and an Agilent 5977B mass spectrometer for method execution.

Methodology and Instrumentation

Sample Preparation and Extraction

• Volume: 5 mL water plus 2 g NaCl in 20 mL headspace vial
• Incubation: 5 min at 40 °C, stirring at 1 000 rpm
• Extraction: 3 min headspace equilibrium with SPME device
• Desorption: 4 min in splitless inlet at 290 °C

GC/MS Conditions

• GC: Agilent 7890B, J&W CP-Sil 5 CB column (30 m × 0.25 mm × 1.00 µm)
• Carrier gas: Helium, constant flow 1 mL/min
• Oven program: 30 °C (4 min) to 130 °C at 4 °C/min (1 min hold)
• MS: Agilent 5977B, scan mode, solvent delay 7.5 min, source temp 280 °C, quad temp 150 °C

Main Results and Discussion

Calibration and Linearity

• SPME fiber: R2 ≥ 0.991 for all BTEX components
• SPME Arrow: R2 ≥ 0.993, reflecting improved response at the low end (0.6 ppb)

Detection Limits

• Fiber MDL range: 0.20–0.43 ppb; LOQ range: 0.68–1.45 ppb
• Arrow MDL range: 0.04–0.08 ppb; LOQ range: 0.15–0.26 ppb

Repeatability and Accuracy

• Eight replicates at 0.6 ppb: Arrow RSD 2–4 %, Fiber RSD up to 25 %
• Average error: Arrow ≤ 10 %, Fiber up to 20 %

Real-Sample Analysis

• Three drinking water sources (filtered, tap, lab sink) showed BTEX levels below MDL or LOQ

The enhanced extraction phase of the Arrow device, combined with salt addition, increased partitioning of BTEX into the headspace, yielding lower detection limits and higher precision.

Benefits and Practical Applications

The HS-SPME Arrow method offers:

• Sub-ppb sensitivity for regulatory monitoring of water sources
• Improved mechanical robustness and longer device lifetime
• Automated operation for high throughput in environmental and QA/QC laboratories

Future Trends and Potential Applications

Advances in SPME technology may include integration with field-deployable samplers, further miniaturization of extraction devices and coupling with high-resolution mass spectrometry. Expansion to a broader range of VOCs and real-time monitoring platforms will support rapid on-site assessments of water quality.

Conclusion

This study demonstrates that headspace SPME Arrow significantly outperforms the conventional SPME fiber in sensitivity, linearity and repeatability for BTEX analysis in water. The method meets the stringent requirements of environmental monitoring and offers a reliable, automated workflow for routine laboratory testing.

Reference

• Analysis of BTEX in Natural Water with SPME. Agilent Application Note SI-01251. September 2010.