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

Significance of the topic

Analysis of mineral oil hydrocarbon fractions in environmental samples is critical for pollution monitoring and regulatory compliance. Traditional GC-FID methods for total petroleum hydrocarbons require lengthy temperature programming and long cycle times, limiting laboratory throughput.

Objectives and study overview

This application explores the use of a low thermal mass GC oven to accelerate hydrocarbon oil index analysis. Key goals include reducing total cycle time below five minutes, enhancing sensitivity, and maintaining method compliance for the C10–C40 fraction in soil and water extracts.

Methodology and instrumentation

Samples spiked with even-numbered n-alkanes (C10-C40) and a diesel/motor oil composite standard were prepared in hexane. Fast GC-FID separation was achieved on an Agilent 7890A equipped with a low thermal mass (LTM) oven module and a 10 m × 0.32 mm DB-5HT column. Splitless injection at 350 °C was used, with an oven program of 40 °C (0.5 min), ramping to 240 °C at 200 °C/min, then to 340 °C at 100 °C/min, for a total run time of three minutes and a cool-down to 40 °C in under two minutes.

Used Instrumentation

• Agilent 7890A gas chromatograph
• Low thermal mass oven module with 10 m DB-5HT column (0.32 mm id, 0.1 µm film)
• Split/splitless inlet (SSI) with 350 °C program
• Agilent 7683B or 7693A autosampler
• Flame ionization detector (FID)

Main results and discussion

Retention time repeatability for C10, C20, and C40 was excellent (<0.003 min, <0.1% RSD) and peak area repeatability below 1% RSD. Discrimination ratios (C40/C20 = 0.899) exceeded the 0.80 threshold. Calibration from 40 to 1000 mg/L showed linearity (r2 > 0.999) and limit of detection below 25 mg/L. Fast programming compressed the hydrocarbon hump, boosting signal intensity compared to a standard 21 min oven run.

Benefits and practical applications

The LTM system achieves a five-minute injection-injection cycle, improving throughput six-fold while meeting ISO 9377 performance criteria. Splitless injection ensures robust performance for diverse matrices, and fixed integration windows allow automated data processing without manual intervention.

Future trends and potential applications

Adoption of LTM technology can be extended to other fast GC applications, including volatile organic compounds and semi-volatiles. Integration with mass spectrometry could further enhance selectivity. Advances in automation and data analytics will streamline high-throughput environmental monitoring workflows.

Conclusion

Incorporating a low thermal mass oven into an Agilent 7890A GC-FID dramatically reduces analysis time for mineral oil hydrocarbon fractions to three minutes, with total cycle time under five minutes. The method delivers excellent repeatability, sensitivity, and compliance with regulatory standards, offering a powerful solution for high-throughput environmental analysis.

References

• International standard ISO 9377-2 Water Quality Determination of hydrocarbon oil index part 2 Method using solvent extraction and gas chromatography 2000
• B Wuest Agilent Technologies application note 5988-0621EN 2000