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

Significance of the Topic

The precise separation and quantification of hydrocarbon fractions in diesel and mineral oil samples are fundamental to quality control in the fuel and petrochemical industries. Gas chromatography with flame ionization detection (GC-FID) remains a gold standard for hydrocarbon profiling because of its robustness, sensitivity, and reproducibility under high‐temperature conditions.

Objectives and Study Overview

This application note evaluates a standardized method for analyzing a Diesel #2/mineral oil standard using a high‐temperature Rxi®-5HT capillary column. Key goals include achieving baseline separation of representative n-alkanes (C12, C16, C20), optimizing chromatographic conditions, and demonstrating method suitability for routine quality assurance.

Methodology and Instrumentation

The study employs split injection of a 5,000 ng/µL diesel/mineral oil standard in hexane. A 1 µL aliquot is introduced into a GC inlet equipped with a premium precision liner packed with wool, maintained at 275 °C. The Rxi®-5HT capillary column (15 m × 0.25 mm ID × 0.10 µm film) is heated from 40 °C (0.1 min hold) to 400 °C at 19.6 °C/min, with a final hold of 1.53 min. Hydrogen serves as the carrier gas in constant flow mode at 1.75 mL/min. The FID is operated at 420 °C, using nitrogen make-up gas (50 mL/min), hydrogen (40 mL/min), and air (450 mL/min). Data acquisition occurs at 20 Hz.

Instrumentation Used

• Gas chromatograph: Agilent/HP 6890 GC
• Column: Restek Rxi®-5HT, 15 m × 0.25 mm ID × 0.10 µm film thickness
• Inlet liner: Premium 4 mm precision liner with wool
• Detector: Flame ionization detector at 420 °C
• Carrier gas: Hydrogen; make-up gas: Nitrogen

Main Results and Discussion

Under the described conditions, the standard exhibited well-resolved peaks for n-dodecane (C12), n-hexadecane (C16), and n-eicosane (C20) at retention times of approximately 203.5 s, 349.2 s, and 468.8 s, respectively. The high-temperature program enabled elution of higher boiling components without column degradation. Calculated column length, adjusted for holdup time, confirmed an effective length of 15.7 m, ensuring reliable retention indices.

Practical Benefits and Applications

This method offers a rapid, reproducible approach for routine hydrocarbon profiling in Diesel #2 and mineral oil samples. The robust temperature program and optimized flow parameters facilitate high throughput in quality assurance laboratories. Its applicability extends to batch release testing, contamination screening, and compliance with regulatory standards.

Future Trends and Applications

Emerging trends include coupling high-temperature GC with mass spectrometry for enhanced compound identification and leveraging automated sample preparation to increase laboratory efficiency. Integration with advanced data analytics and machine learning may enable predictive maintenance of GC systems and deeper insights into complex hydrocarbon mixtures.

Conclusion

The validated GC-FID method on the Rxi®-5HT column provides a reliable, high‐temperature solution for the separation and quantification of key n-alkanes in diesel and mineral oil standards. Its robustness and reproducibility make it a valuable tool for industrial quality control and research applications.