High Throughput Mineral Oil Analysis (Hydrocarbon Oil Index) by GC-FID using the Agilent Low Thermal Mass (LTMII) System

Importance of Topic

The rapid and sensitive determination of mineral oil contamination in environmental matrices is critical for assessing pollution levels in soil and water. Traditional GC-FID methods for hydrocarbon oil index (HOI) or total petroleum hydrocarbons (TPH) can be time-consuming and limit laboratory throughput. Integrating low thermal mass (LTM) technology addresses these challenges by drastically reducing analysis time while maintaining regulatory compliance and analytical performance.

Objectives and Study Overview

This study aimed to develop and validate a fast GC-FID method for mineral oil analysis (C10–C40 fractions) using the Agilent LTM II system. Key goals included meeting ISO 9377-2 performance criteria—solvent separation, retention time reproducibility, solute discrimination, and linearity—while achieving a minimum analysis cycle time.

Methodology and Instrumentation

Sample preparation followed solvent extraction with hexane, cleanup over Florisil, and concentration by nitrogen blowdown. An n-alkane standard (C10–C40) and synthetic mineral oil mixture (diesel/motor oil) served for system suitability and calibration. The Agilent 7890A GC equipped with a splitless inlet (SSl), flame ionization detector (FID), and a five-inch Low Thermal Mass (LTM II) oven module was operated in constant helium flow. Fast oven programming ramped from 40 °C to 340 °C in under 3 minutes with rapid cool-down to 40 °C in 2 minutes.

Key Results and Discussion

• Retention time repeatability for C10, C20, and C40 showed RSD < 0.03%, confirming precise thermal control.
• Peak area RSDs were below 1% for alkanes and approximately 0.6% for the mineral oil mixture at 400 mg/L.
• Solute discrimination ratios (C40/C20 = 0.92, C10/C20 = 0.95) surpassed the 0.80 requirement, demonstrating minimal bias with splitless injection.
• Calibration linearity across 40–1000 mg/L yielded R² > 0.999, with a detection limit below 25 mg/L.
• Compared to a standard 21 min oven program, LTM II compressed the hydrocarbon profile into a 3 min run, boosting peak height and improving sensitivity.

Benefits and Practical Applications

The LTM II-based method reduces total cycle time to 5 minutes (injection to injection), increases sample throughput by over sevenfold, and lowers per-sample costs. Its robust splitless injection minimizes discrimination for both clean and heavily contaminated extracts. These attributes suit environmental laboratories performing high-volume soil and water monitoring, quality assurance, and regulatory compliance.

Future Trends and Opportunities

Emerging applications may integrate LTM technology with tandem mass spectrometry for enhanced selectivity, or with automated sample preparation platforms to create fully integrated high-throughput workflows. Further miniaturization of LTM modules could enable portable field-deployable systems for on-site screening of petroleum hydrocarbon spills.

Conclusion

Incorporating the Agilent LTM II system into GC-FID workflows for mineral oil analysis meets stringent method requirements while yielding dramatic improvements in analysis speed, reproducibility, and sensitivity. The optimized protocol delivers a reliable, high-throughput solution for environmental monitoring of hydrocarbon contamination.

References

• International Organization for Standardization. ISO 9377-2:2000. Water Quality – Determination of Hydrocarbon Oil Index – Part 2: Method Using Solvent Extraction and Gas Chromatography.
• Wuest, B. Agilent Technologies Technical Publication 5988-0621EN (2000). Fast GC-FID Analysis of Mineral Oil Using Low Thermal Mass Technology.