Analysis of mineral oil in environmental samples according to H53

Importance of the Topic

Mineral oil hydrocarbons (MOH) are widespread pollutants due to extensive processing and use of crude oil products in fuels, lubricants, and heating oils. Because MOHs are resistant to biodegradation, monitoring their presence in environmental matrices such as water, soil, and sludge is essential to protect ecosystems and ensure regulatory compliance (EN ISO 9377-2 and ISO 16703:2011).

Objectives and Study Overview

This study outlines an optimized gas chromatography method with flame ionization detection (GC-FID) using on-column injection (OCI) to quantify MOHs in environmental samples. The method aims to achieve non-discriminatory injection over a wide boiling range (C10–C40) and to shorten analysis time through appropriate column configurations and alternative carrier gases.

Methodology and Instrumentation

• Sample Preparation: Water samples extracted and cleaned with Florisil to remove polar compounds; soil and sludge prepared similarly under ISO 16703.
• Chromatographic Setup: Shimadzu Nexis GC-2030 with OCI-2030 injector; SH-Mxt-1 analytical column (15 m×0.25 mm ID, 0.10 μm film) combined with a deactivated retention gap (0.5 m×0.53 mm ID).
• Injection Strategy: Direct on-column injection to minimize discrimination across boiling range; target area ratio C40/C20 ≥0.8 per ISO 9377-2.
• Calibration: Seven-point external calibration (0–5 mg/mL) using commercial diesel lubricating oil mixtures and n-decane/n-tetracontane standards, achieving R² >0.9999.
• Carrier Gas Options: Helium for standard operation; hydrogen evaluated for higher linear velocities and reduced runtimes.

Main Results and Discussion

• Injection Performance: OCI provided an alkane area ratio C40/C20 >0.98 with helium, indicating minimal discrimination; C40 eluted at 7.4 min.
• Calibration Quality: Linear response across 0–5 mg/mL with R² >0.9999.
• Real Sample Analysis: Environmental extracts exhibited MOH concentrations within the calibration range, confirming method applicability.
• Alternative Configurations: A simple on-column liner with Rxi-1HT column yielded similar performance; hydrogen as carrier gas reduced C40 retention to 6.4 min and total runtime below 7 min while maintaining resolution.

Benefits and Practical Applications

• Robust quantification of MOHs in water, soil, and sludge without the need for compound-specific identification.
• Short analysis times (<8 min) increase laboratory throughput and reduce carrier gas consumption.
• Flexibility in column and carrier gas selection allows adaptation to instrument availability and supply constraints.

Future Trends and Applications

• Expansion to other complex hydrocarbon mixtures and emerging contaminants using advanced detectors or two-dimensional GC.
• Integration with automated sample preparation for high-throughput monitoring in regulatory and industrial settings.
• Adoption of hydrogen carrier gas as a sustainable alternative to helium amid global supply concerns.

Conclusion

The described GC-FID method with on-column injection offers a fast, accurate, and versatile approach for routine MOH analysis in environmental samples. Its compliance with international standards and adaptability to alternative carrier gases make it a valuable tool for analytical and environmental laboratories.

References

• EN ISO 9377-2: Water quality — Determination of mineral oil hydrocarbons (C10–C40) — Part 2: Gas chromatography with flame ionization detector (GC-FID).
• ISO 16703:2011: Water quality — Determination of hydrocarbon oil index — Infrared spectrometric method.