Diesel #2/Mineral Oil Standard on Rxi®-1HT (15 m x 0.25 mm x 0.10 μm)

Significance of the Topic

The analysis of diesel fuel and mineral oil fractions is critical for quality control, regulatory compliance and environmental monitoring. Precise separation and quantification of hydrocarbon chains in the C12–C20 range ensures product consistency, performance characteristics and safety in industrial applications.

Objectives and Study Overview

This application note demonstrates a robust gas chromatographic method using a high‐temperature capillary column to separate and identify key n‐alkanes in a Diesel #2/mineral oil standard. The primary goals are to establish retention times for C12, C16 and C20, verify column performance and optimize parameters for fast, reproducible analysis.

Methodology

A 5,000 ng/µL solution of Diesel #2/mineral oil was prepared in hexane. A 1 µL aliquot was injected in split mode (10:1) onto a 15 m×0.25 mm×0.10 µm Rxi-1HT column. The temperature program started at 40 °C (0.1 min hold), ramped at 20 °C/min to 400 °C (1.9 min hold). Hydrogen served as the carrier gas at constant 1.75 mL/min. Detection was accomplished by flame ionization (FID) at 420 °C with nitrogen make-up gas.

Instrumentation Used

• Gas Chromatograph: Agilent/HP 6890 GC
• Column: Rxi-1HT, 15 m (calculated 15.7 m effective length), 0.25 mm ID, 0.10 µm film (Restek cat. #13950)
• Injector: Premium 4 mm precision liner with wool (Restek cat. #23305.5), 275 °C
• Carrier Gas: Hydrogen, constant flow at 1.75 mL/min
• Detector: FID at 420 °C; make-up gas N2 at 50 mL/min; H2 at 40 mL/min; air at 450 mL/min
• Data Rate: 20 Hz

Main Results and Discussion

The optimized method achieved baseline separation of key n‐alkanes. Observed retention times were: C12 at 195.2 s, C16 at 337.6 s and C20 at 455.3 s. The rapid temperature ramp and high‐temperature column film allowed efficient elution of higher‐boiling components within a one‐hour runtime. Chromatographic peaks exhibited sharp, symmetric profiles, indicating minimal column bleed and stable flow dynamics.

Benefits and Practical Applications of the Method

• Fast, reliable separation of mid‐chain hydrocarbons for routine quality checks.
• High thermal stability enables wide‐range temperature programming without column degradation.
• Sensitive detection with FID supports low‐level quantification in complex matrices.
• Applicable to petroleum, petrochemical and environmental sample analyses.

Future Trends and Potential Uses

Advanced stationary phases and shorter, high‐efficiency columns may further reduce analysis times. Integration with mass spectrometry can provide structural confirmation of coeluting compounds. Automated sample preparation and two‐dimensional GC techniques will expand the method’s applicability to complex hydrocarbon mixtures and trace‐level studies.

Conclusion

The described GC-FID method on an Rxi-1HT column offers a rapid, reproducible approach for the separation and quantitation of C12–C20 n-alkanes in Diesel #2/mineral oil standards. Its robustness and sensitivity make it suitable for industrial QA/QC workflows and environmental monitoring.

References

• Restek Corporation. Application Note: Diesel #2/Mineral Oil Standard on Rxi-1HT (15 m x 0.25 mm x 0.10 µm).