Automated Determination of Gasoline Range Organics (GRO) in Water Via Valve-and-Loop Headspace GC

Importance of the Topic

The monitoring of gasoline range organics (GRO) in water is critical due to the environmental and health risks associated with petroleum hydrocarbon contamination. Automated headspace gas chromatography provides a fast, reliable screening method for C6–C10 hydrocarbons, enabling timely assessments of water quality.

Objectives and Study Overview

This work aimed to optimize an automated analytical workflow for the determination of GRO in water, following EPA methods. The study focused on achieving high sensitivity, reproducibility, and throughput using a valve-and-loop headspace GC system.

Methodology and Instrumentation

The analytical protocol involved the following key steps:

• Sample preparation: 5 mL water in a 20 mL vial, sealed with aluminum crimp caps.
• Headspace conditions: equilibration at 85 °C for 25 min with high-speed shaking; manifold and transfer line held at 95 °C; vial pressurization at 1 bar.
• Injection: 1 mL loop filled under 0.5 bar, 0.5 min injection time, followed by line purge.
• GC-FID analysis: TRACE 1310 GC with TR-1 column (30 m × 0.32 mm × 3 µm), helium carrier at 3 mL/min, injector at 150 °C (split 20:1), FID at 300 °C.
• Calibration: seven-point curves from 10 ppb to 100 ppm using a certified PVOC/GRO standard.

Key Findings and Discussion

Calibration exhibited excellent linearity (R² > 0.9997) across all target analytes. The separation resolution between ethylbenzene and m/p-xylene reached 1.83, ensuring reliable peak integration. Repeatability tests at 1 ppm showed relative standard deviations below 1.5% for all compounds. Blank runs confirmed absence of carryover, and spiked tap water chromatograms demonstrated clear analyte detection.

Benefits and Practical Applications

The automated headspace GC-FID system delivers high sample throughput with minimal operator intervention. Inert sample pathways and temperature-controlled components reduce carryover and enhance data consistency. The platform is well-suited for routine environmental monitoring, regulatory compliance testing, and preliminary site assessments.

Future Trends and Applications

Potential developments include coupling with mass spectrometry for increased selectivity, miniaturized or portable headspace units for field analysis, and integration of data-driven algorithms to automate peak identification and quality control. Expanding the approach to broader volatile organic compound classes could further extend its environmental applications.

Conclusion

The combination of the TriPlus 300 autosampler, TRACE 1310 GC, and Chromeleon CDS offers a robust, automated solution for GRO determination in water. The method meets stringent performance criteria for linearity, precision, and throughput, supporting efficient environmental screening workflows.

References

• Interlaboratory Study of Three Methods for Analyzing Petroleum Hydrocarbons in Soils. API Publication 4599, American Petroleum Institute, March 1994.
• U.S. Environmental Protection Agency. Method 5021A: Volatile Organic Compounds in Soil and Waste Samples by Static Headspace Analysis.
• U.S. Environmental Protection Agency. Method 8015D: Nonhalogenated Organics Using GC/FID.