Diesel #2/Motor Oil Standard on Rxi®-5HT (15 m x 0.25 mm x 0.10 μm)

Importance of the Topic

Accurate analysis of diesel and motor oil fractions is essential in petroleum laboratories, environmental monitoring, and quality control. Gas chromatography with a high temperature resistant column provides fast and reliable separation of high boiling hydrocarbons.

Study Objectives and Overview

This method aims to establish a robust GC procedure for quantifying C16, C18, C22, and C24 alkanes in a Diesel #2/motor oil standard. The procedure demonstrates reproducibility, resolution, and speed using an Rxi-5HT column.

Methodology

Sample preparation and chromatographic conditions are optimized for high boiling point compounds.

• Sample: Diesel #2/motor oil diluted in hexane to 5000 ng/µL
• Injection: 1 µL split 10 to 1 in a wool packed liner at 275 °C
• Carrier gas: hydrogen at 1.75 mL/min constant flow
• Oven program: 40 °C hold for 0.1 min then ramp at 19.6 °C/min to 400 °C, hold 1.53 min
• Detector: flame ionization at 420 °C with nitrogen make up
• Data rate: 20 Hz

Used Instrumentation

• Gas chromatograph: Agilent 6890 GC
• Column: Rxi-5HT, 15 m x 0.25 mm ID x 0.10 µm film thickness
• Precision liner: 4 mm wool packed

Main Results and Discussion

The method achieved clear separation of target alkanes with retention times of 349.1 s (C16), 412.1 s (C18), 521.2 s (C22), and 569.3 s (C24). Baseline resolution and reproducible retention times indicate the suitability of the column for high molecular weight hydrocarbons. The actual column length was determined at 15.7 m using holdup time calculations.

Benefits and Practical Applications

• Rapid and reproducible analysis of diesel and motor oil fractions
• High resolution of mid to high carbon number alkanes
• Applicable to QC labs and research in petroleum analysis

Future Trends and Applications

• Integration with automated sampling systems for high throughput
• Coupling with mass spectrometry for detailed compositional profiling
• Development of shorter columns with optimized phases for faster runs
• Implementation in field portable GC instruments for on site analysis

Conclusion

The presented GC method on an Rxi-5HT column offers a reliable approach for quantifying C16 to C24 alkanes in diesel and motor oil standards. Its robust performance and high throughput capabilities make it valuable for diverse applications in analytical laboratories.