Arabian Medium Crude Oil on Rxi®-1HT (15 m x 0.25 mm x 0.10 μm)

Analysis of Arabian Medium Crude Oil on Rxi-1HT Column

Importance of the Topic

The detailed profiling of hydrocarbons in crude oil is essential for refining optimization, quality control, and environmental monitoring. Precise separation and quantification of n-alkanes enable better understanding of feedstock properties and inform downstream processing decisions.

Study Objectives and Overview

This study demonstrates a gas chromatography method for separating mid-range n-alkanes in Arabian medium crude oil using a Restek Rxi®-1HT capillary column. The goal is to achieve fast, reproducible retention of key hydrocarbon fractions (C10–C40) under a high-temperature program.

Methodology and Instrumentation

• Column: Rxi®-1HT, 15 m × 0.25 mm ID, 0.10 µm film thickness (cat. # 13950)
• Gas Chromatograph: Agilent/HP 6890 GC equipped with FID detector
• Carrier Gas: Hydrogen, constant flow at 1.75 mL/min; make-up gas nitrogen at 50 mL/min
• Injection: 1 µL split injection (10:1) using a 4 mm precision liner with wool; injector temperature 275 °C
• Oven Program: 40 °C (0.1 min hold) ramped to 400 °C at 20 °C/min, final hold 1.9 min
• Detector Settings: FID at 420 °C; hydrogen flow 40 mL/min; air flow 450 mL/min; data rate 20 Hz
• Sample Preparation: Arabian medium crude diluted in methylene chloride to 50,000 ng/µL

Main Results and Discussion

Key retention times were observed as follows: C10 at 119.1 s, C20 at 456.0 s, and C30 at 678.3 s. The effective column length was calculated at 15.7 m based on holdup time using EZGC® flow calculations. The Rxi-1HT phase sustained a 400 °C final temperature, enabling elution of higher carbon number hydrocarbons (up to C40) within approximately 1000 s, with sharp peaks and good resolution.

Benefits and Practical Applications

• Rapid and reliable profiling of hydrocarbon distributions in crude oil samples
• Short analysis times increase laboratory throughput
• Applicable for refinery feedstock evaluation, QA/QC, and environmental assessments

Future Trends and Applications

The integration of advanced detectors such as GC-MS or time-of-flight MS may enhance identification and quantitation of complex fractions. Automation of sample preparation and application of chemometric tools can further streamline analysis and support real-time monitoring of crude oil quality.

Conclusion

The high-temperature GC method using the Rxi-1HT column provides an efficient, robust approach for separating n-alkanes in Arabian medium crude oil over a wide carbon range. Its speed, thermal stability, and reproducibility make it a valuable asset for petrochemical laboratories and industrial quality control.

Reference

Restek Corporation. Arabian Medium Crude Oil on Rxi-1HT Application Note.