Volatile organic compounds in water by purge and trap/capillary column GC with photoionization and electrolytic conductivity detectors in series

Significance of the Topic

Ensuring the safety of drinking water requires reliable detection of a wide range of volatile organic compounds (VOCs). The 1986 amendments to the US Safe Drinking Water Act expanded regulatory limits to include eight new compounds and monitor fifty-one others. Accurate VOC analysis protects public health, informs treatment strategies, and maintains compliance with environmental regulations.

Objectives and Overview of the Study

This application note outlines the adaptation of EPA Method 502.2 for VOC analysis, employing purge-and-trap sampling followed by capillary column gas chromatography (GC). Key goals include improved resolution, lower detection limits, and dual-detection confirmation by photoionization detector (PID) for aromatics and electrolytic conductivity detector (ELCD) for halocarbons.

Methodology and Instrumentation

• Purge and Trap: A Tenax–silica gel–charcoal trap concentrates VOCs via an 11-minute helium purge.
• Capillary GC Column: A 624-type (6% cyanopropylphenyl/94% methyl, 0.53 mm x 30 m, 3 µm film) or CP-Select 624 CB column ensures high resolution.
• Oven Program: 10 °C hold for 10 min, ramp at 5 °C/min to 160 °C, hold for 0 min.
• Carrier Gas: Helium at 6.0 mL/min.
• Detectors in Series: PID detects aromatic VOCs; ELCD targets halogenated compounds.
• Column Selector: Automated switching between primary and confirmatory columns enables two-column confirmation and unattended operation.

Main Results and Discussion

The optimized capillary method achieved clear separation of 37 target VOCs at 20 ppb concentration. Dual-column validation and dual-detector response ratios (e.g., halogenated aromatics) enhanced compound confirmation. Chromatograms demonstrated consistent retention time shifts and reversed elution orders between columns, streamlining the identification process.

Benefits and Practical Applications

• Lower Detection Limits: Capillary columns provided improved sensitivity over packed columns.
• Enhanced Resolution: Complex VOC mixtures are resolved effectively, reducing coelution risks.
• Automated Confirmation: Column selector and dual detectors minimize manual intervention and increase throughput.
• Regulatory Compliance: Method aligns with EPA 502.2 requirements for drinking water testing.

Future Trends and Opportunities

Advances in microtrap materials, faster oven programs, and enhanced detector technologies (e.g., tandem MS) could further lower detection limits and expand analyte coverage. Integration with remote monitoring networks and real-time data analytics may provide continuous water quality surveillance and rapid response capabilities.

Conclusion

The purge-and-trap capillary GC method with PID/ELCD detection offers a robust, sensitive, and automatable solution for comprehensive VOC analysis in water. It meets stringent regulatory standards and supports high-throughput laboratory workflows.

Reference

Agilent Technologies. Application Note: Volatile organic compounds in water by purge and trap/capillary column GC with photoionization and electrolytic conductivity detectors in series. 2011.