Validation of New VPH GC/MS Method using Multi-Matrix Purge and Trap Sample Prep System

Validation of a New VPH GC/MS Method Using Multi-Matrix Purge and Trap Sample Preparation

Significance of the Topic

The accurate measurement of volatile petroleum hydrocarbons (VPH) in water and soil is critical for environmental monitoring, regulatory compliance, and human health protection. Leaks from underground storage tanks and other sources can release volatile aliphatics and aromatics into the environment, many of which carry established health risks at low concentrations. A reliable analytical approach that achieves low detection limits, high precision, and robustness across multiple matrices supports timely risk assessment and remediation efforts.

Objectives and Study Overview

This study aimed to validate the draft Massachusetts Department of Environmental Protection (MassDEP) GC/MS method for VPH quantification, replacing previous FID/PID detectors with mass spectrometric detection. Validation covered both aqueous and soil matrices and assessed calibration performance, method detection limits (MDLs), and overall suitability of the Teledyne Tekmar Atomx automated purge and trap sample preparation system.

Methodology and Used Instrumentation

The validation employed automated purge and trap extraction using the Teledyne Tekmar Atomx platform. Water samples were purged directly, while soil samples underwent an automated methanol extraction protocol. Extracts were thermally desorbed and introduced into an Agilent 7890A GC coupled to a 5975C inert XL MSD with a triple-axis detector. Key conditions included:

• Restek RTX-502.2 column (30 m × 0.25 mm ID × 1.4 µm)
• Oven program: 50 °C hold, ramp 11 °C/min to 130 °C, then 20 °C/min to 250 °C
• Purge parameters: up to 11 min at 40 mL/min, dry purge and bake steps to remove residual volatiles
• MS detection: scan m/z 35–250, source 250 °C, quad 200 °C

Main Results and Discussion

Calibration curves for 18 target and surrogate analytes showed excellent linearity (r² ≥ 0.995) over 1–200 ppb. Method detection limits ranged from 0.07 ppb for naphthalene to 0.23 ppb for total C5–C8 aliphatics, meeting or surpassing regulatory requirements. A representative total ion chromatogram of a 10 ppb standard demonstrated clear resolution of aliphatic and aromatic components. The automated soil extraction reduced hands-on time and achieved comparable sensitivity to water analyses using water-based calibration standards.

Benefits and Practical Applications

• Low MDLs enable detection well below Massachusetts regulatory limits (0.2–0.7 mg/L).
• Mass spectrometric detection offers enhanced selectivity and confirmation ion monitoring.
• Automated purge and trap sample prep increases throughput and reproducibility.
• Automated methanol extraction for soils streamlines workflows and reduces solvent handling.

Future Trends and Opportunities

• Expansion of target compound lists to include emerging volatile contaminants.
• Integration of isotopically labeled internal standards for improved quantitation accuracy.
• Automation of data processing and real-time reporting in laboratory information management systems (LIMS).
• Adaptation of purge and trap methods for field-deployable instrumentation and on-site monitoring.

Conclusion

The validated GC/MS method using the Teledyne Tekmar Atomx system meets MassDEP calibration and sensitivity criteria for volatile petroleum hydrocarbons in both water and soil. Mass spectrometric detection simplifies the analytical setup, and automated sample preparation enhances laboratory efficiency. Once finalized, this approach can become a standard protocol for routine environmental monitoring and regulatory compliance.

References

• Method for the Determination of Volatile Petroleum Hydrocarbons (VPH) by Gas Chromatography/Mass Spectrometry, Massachusetts Department of Environmental Protection, February 2012.
• Drinking Water Contaminants, United States Environmental Protection Agency, http://water.epa.gov/drink/contaminants/index.cfm.