Determination of VOC’s in aqueous samples by using Purge & Trap – GCMSD

Significance of the Topic

Volatile organic compounds (VOCs) at trace levels in water pose significant environmental and health risks. Regulatory bodies worldwide, including the Italian DLGS 152/2006 and the U.S. EPA methods, now mandate detection limits down to 1 ppt for key contaminants. Developing robust, sensitive, and cost-effective analytical workflows without reliance on cryofocusing addresses both regulatory compliance and practical laboratory demands.

Objectives and Study Overview

This study aimed to establish a purge & trap–GC-MS method capable of quantifying 1,2-dibromoethane and 1,2,3-trichloropropane in aqueous samples at or below 1 ppt without using a cryofocusing step. Performance parameters—including linearity, accuracy, repeatability, and extraction efficiency—were evaluated against direct liquid injection.

Methodology and Instrumentation

Sample preparation employed a 25 mL water sparge in an EST Analytical ENCON Evolution purge & trap unit integrated with an EST Analytical CENTURION autosampler. The system automatically added 5 µL of a 10 ppb internal standard mix (fluorobenzene, chlorobenzene-d5, 1,4-dichlorobenzene-d4) and a surrogate mix (1,2-dichloroethane-d4, toluene-d8, 4-bromofluorobenzene).
Chromatographic separation used an Agilent 7890B GC with a split/splitless injector (split 1:10) and a 20 m × 180 µm × 1.0 µm DB-624 Ultra Inert column at 0.8 mL/min. Detection was carried out on an Agilent 5977A MSD equipped with an Extract Ion Source, operated in selected ion monitoring (SIM) mode.

Main Results and Discussion

• Calibration curves for 35 target VOCs, including 1,2-dibromoethane and 1,2,3-trichloropropane, were linear over 0.1–50 ppt (R² ≥ 0.997).
• Accuracy ranged 80–120% at most levels; at 0.1 ppt, accuracy was 123% and 122% for the two key analytes.
• Repeatability at 1 ppt showed RSDs of 2.0% (1,2-dibromoethane) and 1.8% (1,2,3-trichloropropane) over eight injections.
• Internal standard RSDs averaged 2.0%, confirming stable automated addition.
• Extraction efficiency compared favorably with direct liquid injection, yielding comparable response magnitudes.

Benefits and Practical Applications

• Eliminates the need for cryofocusing and liquid nitrogen, reducing cost and complexity.
• Achieves sub-ppt detection for challenging halogenated VOCs.
• Automates sample handling and standard addition to boost throughput and reproducibility.
• Meets stringent environmental monitoring and QA/QC requirements in water analysis.

Future Trends and Potential Applications

• Integration with high-resolution MS for broader compound screening.
• Miniaturization of purge & trap modules for field deployment.
• Development of green sorbent materials to improve analyte recovery.
• Coupling with on-line sampling and data analytics for real-time monitoring.

Conclusion

The developed P&T–GC-MS method using EST Analytical ENCON/CENTURION and Agilent 7890B/5977A instrumentation reliably quantifies key VOCs at ppt levels without cryofocusing. High linearity, accuracy, and repeatability demonstrate its suitability for regulatory compliance and routine environmental analysis.

Used Instrumentation

• EST Analytical ENCON Evolution Purge & Trap (25 mL sparger)
• EST Analytical CENTURION Autosampler
• Agilent 7890B Gas Chromatograph with S/SL injector (split 1:10)
• DB-624 Ultra Inert column (20 m × 180 µm × 1.0 µm, 0.8 mL/min)
• Agilent 5977A MSD with Extract Ion Source, SIM acquisition