The Determination of Low Level Benzene, Toluene, Ethyl Benzene, and Xylenes (BTEX) in Drinking Water by Headspace Trap GC/MS

Significance of the Topic

Water contamination with volatile aromatic hydrocarbons such as benzene, toluene, ethyl benzene and xylenes poses significant risks to public health and must be monitored at sub-ppb levels to meet regulatory standards. BTEX compounds are classified as toxic pollutants with benzene recognized as a carcinogen, making their reliable detection in drinking water essential.

Objectives and Study Overview

This application note evaluates a headspace trap GC/MS method designed to exceed the EPA Method 524.2 detection requirements for BTEX in drinking water. The primary goals include enhancing detection sensitivity, ensuring compliance with regulatory criteria, reducing analysis time, and improving water management compared to traditional purge-and-trap techniques.

Methodology and Instrumentation

• Sample Preparation: Volatilization and concentration of BTEX using PerkinElmer TurboMatrix Headspace Trap.
• Concentration Trap: Inline Carbopack B & X trap ramped from 35 °C to 260 °C to focus analytes.
• GC/MS System: PerkinElmer Clarus SQ 8S Mass Spectrometer with standard-capacity turbo molecular pump operated in full scan mode (35–350 amu).
• Analytical Column: Elite 624, 20 m × 0.18 mm × 1.0 μm for rapid, high-efficiency separation.
• Headspace Conditions: Sample at 80 °C, needle at 110 °C, transfer line at 120 °C, 8 min equilibration, 2 min dry purge, 2.5 min trap hold.
• GC Conditions: Oven held at 40 °C (0.5 min), ramped at 35 °C/min to 185 °C; helium carrier at 1 mL/min initial flow; total run time of 4 min.
• MS Conditions: Electron impact ionization, filament delay 1.5 min, scan speed 0.15 sec, interscan delay 0.04 sec, ion source at 200 °C, transfer line at 200 °C.

Main Results and Discussion

A 12-point calibration curve demonstrated excellent linearity (r2 ≥ 0.9993) from 0.02 to 60 ppb for all BTEX analytes. Signal-to-noise ratios at the 0.02 ppb level ranged from 240:1 (o-xylene) to 670:1 (m,p-xylenes). Precision tests at 1.0 ppb yielded relative standard deviations below 3% for each compound. Chromatograms recorded at 4.0 ppb confirmed clear separation within a 4-minute cycle. Water management trials showed that a 2-minute dry purge effectively eliminated water interference, ensuring analyte peaks remained unaffected.

Practical Benefits and Applications

• Superior sensitivity enables detection well below regulatory thresholds.
• Short analysis cycle (~4 min) allows high throughput (up to 72 samples per 12-hour shift).
• Efficient water removal reduces system maintenance and downtime.
• Mass spectrometric detection offers high confidence in analyte identification, minimizing false positives.

Future Trends and Opportunities

Emerging developments may include miniaturized headspace traps, fully automated sample handling, and advanced data analytics (machine learning) for real-time monitoring. Extending this approach to additional volatile organic compounds and integrating portable GC/MS platforms could facilitate on-site water quality assessments.

Conclusion

The headspace trap GC/MS method using the PerkinElmer Clarus SQ 8S provides a fast, sensitive, and robust solution for BTEX analysis in drinking water. It surpasses EPA Method 524.2 requirements, offers excellent linearity and precision, and effectively manages water interference, making it an attractive option for environmental testing laboratories.

Reference

• Marotta L., PerkinElmer Application Note 010004_01, 2011.