Validation of Wisconsin Gasoline Range Organics

Importance of the Topic

Analysis of gasoline‐range organics (C6–C10 hydrocarbons) in water and soil is critical for monitoring environmental contamination from leaking underground storage tanks, pipeline spills, and surface runoff. Reliable measurement of compounds such as MTBE, benzene, toluene, ethylbenzene, xylenes, trimethylbenzenes and naphthalene underpins regulatory compliance, site assessment and remediation strategies.

Objectives and Study Overview

This work aimed to validate the Wisconsin DNR Modified Gasoline Range Organics (GRO) Method using an integrated Atomx Automated VOC Sample Prep System coupled to an Agilent 7890/5975 GC/MS. Key goals included establishing linear calibration, determining method detection limits, and verifying quality control performance for both water and high‐level soil matrices under automated methanol extraction conditions.

Methodology and Instrumentation

The Atomx platform combines an 80‐position multi‐matrix autosampler, automated methanol extraction for soil samples, and a purge‐and‐trap concentrator to streamline sample preparation. Water samples (5 mL) underwent direct purge and trap, while soil samples (7 g) received a 7 mL methanol extraction followed by a 1:100 dilution into water for purge and trap. Separation and detection were performed on an Agilent 7890A GC fitted with a Restek RTX‐VMS column and a 5975C inert XL MSD scanning m/z 35–270. Helium carrier gas, oven temperature programming and split‐inlet parameters adhered to modified Wisconsin GRO specifications.

Main Results and Discussion

• Calibration: A 10–200 ppb range for summed GRO analytes yielded a calibration curve with r²=0.9992 and an average response factor of 6.89×10⁻⁷.
• Quality Control: Replicate laboratory control spikes (RLCS) at 100 ppb in water achieved 106.8% recovery (2.7% RSD); soil RLCS at 10 ppm returned 89.7% recovery (5.9% RSD). Duplicate spikes fell similarly within method limits.
• Detection Limits: Method detection limits (LODs) were 0.160 ppb for water and 0.126 ppb for soil. Limits of quantitation (LOQs) were 0.511 ppb (water) and 0.402 ppb (soil), satisfying Wisconsin GRO thresholds.

Benefits and Practical Applications

The integrated Atomx system reduces manual handling and accelerates throughput by preparing one sample while another is analyzed. Automated surrogate and internal standard addition, methanol extraction, and P&T cleanup minimize labor and carryover, making the workflow suitable for high‐volume environmental and regulatory labs requiring routine groundwater and soil screening.

Future Trends and Potential Applications

As environmental testing demands evolve, future developments may include expansion of automation to additional matrices, incorporation of micro‐extraction and green solvents, coupling with high‐resolution or tandem MS for enhanced specificity, and integration with laboratory information management systems and remote monitoring technologies to further streamline operations.

Conclusion

Validation data confirm that the Atomx automated sample preparation platform coupled to an Agilent 7890/5975 GC/MS meets all performance criteria of the Wisconsin DNR Modified GRO Method for both water and soil matrices. While this study employs MS detection rather than the method’s prescribed FID, the system demonstrates robust accuracy, precision and productivity gains, providing a versatile solution for environmental laboratories.

References

1. Wisconsin DNR. Modified GRO Method for Determining Gasoline Range Organics. PUBL‐SW‐140; September 1995.
2. Chang C; Ji Z. Optimized Analysis of Gasoline (BTEX) in Water and Soil Using GC/FID with Purge and Trap.