Gasoline Range Organics (GRO) by Headspace/GC/FID

Significance of the Topic

The analysis of gasoline range organics (GRO) in environmental samples has gained urgency following high-profile oil spills. GRO components are mobile in water and sediments and pose risks to ecosystems and public health. Efficient, sensitive methods for quantifying GRO in aqueous matrices are crucial for rapid response and regulatory compliance.

Objectives and Study Overview

This study aimed to evaluate static and dynamic headspace sampling using the Teledyne Tekmar HT3™ coupled with an Agilent GC/FID for GRO determination in water. Key objectives included:

• Validating linear calibration ranges covering 2–200 ppb (dynamic) and 50–1000 ppb (static).
• Assessing method compliance with EPA Method 8015C and Wisconsin’s modified GRO protocol.
• Determining method detection limits (MDLs) and recovery rates for target analytes.

Methodology and Instrumentation

• Headspace Analyzer: Teledyne Tekmar HT3™ in static (loop) and dynamic (trap) modes.
• GC/FID System: Agilent 6890A GC with flame ionization detector, Restek Rtx-VMS column (30 m × 0.32 mm × 1.8 µm), helium carrier gas, 20:1 split ratio.
• Static Mode Conditions: Sample equilibration at 75 °C for 10 min, loop transfer at 5 psig, injector transfer at 150 °C.
• Dynamic Mode Conditions: Sweep flow of 200 mL/min, trap desorption at 250 °C, bake flow 200 mL/min, total cycle under 16 min.
• GC Oven Program: 35 °C hold 2 min, ramp 36 °C/min to 180 °C, then 20 °C/min to 225 °C; run time ~8.4 min.

Main Results and Discussion

• Linearity: Dynamic mode (2–200 ppb) and static mode (50–1000 ppb) showed correlation coefficients >0.993 and %RSD <20% for individual GRO compounds.
• Sensitivity: Dynamic mode MDLs ranged from 0.44 to 1.53 ppb; recoveries at 20 ppb were 89.6–98.8%.
• Static Mode Performance: %RSD between 2.0 and 7.8%, correlation coefficients >0.9939 across targets.
• Throughput: Full headspace–GC/FID analysis completed in under 16 minutes per sample, enhancing laboratory productivity.

Benefits and Practical Applications

• Wide dynamic range using one headspace system for trace to elevated concentrations.
• Regulatory compliance with EPA and state methods for nonhalogenated organics.
• Improved sensitivity and reproducibility facilitate monitoring of oil spill impacts and routine water quality assessments.

Future Trends and Opportunities

• Integration with mass spectrometry for enhanced selectivity and confirmation.
• Automated online sampling and real-time monitoring in remote or field-deployable units.
• Application of headspace techniques to complex matrices such as sediments and biota.
• Development of miniaturized traps and micro-GC systems for faster analysis.

Conclusion

The HT3™ headspace GC/FID approach provides rapid, robust, and sensitive analysis of gasoline range organics in water, fulfilling EPA and Wisconsin method requirements with high throughput. This versatile technique supports environmental monitoring and emergency response.

References

• USEPA Method 8015C, Nonhalogenated Organics by Gas Chromatography, Revision 3, February 2007
• Wisconsin DNR PUBL-SW-140, Modified GRO Method for Determining Gasoline Range Organics, September 1995
• USEPA Method 8000B, Determinative Chromatographic Separations, Revision 2, December 1996