EXTENDED HYDROCARBON OIL INDEX ACCORDING TO ISO 9377-2 AND DIN H53 BY GAS CHROMATOGRAPHY

Importance of the Topic

The accurate quantification of dispersed mineral oil in water, covering hydrocarbons from n-C7 to n-C40, is essential for environmental monitoring, industrial wastewater management and regulatory compliance. Extending the traditional hydrocarbon oil index improves detection of lighter fractions in surface and produced waters.

Objectives and Overview

This application note expands ISO 9377-2 and DIN H53 protocols by including n-heptane through n-nonane, while optionally reporting aromatic hydrocarbons. It focuses on measuring dispersed mineral oil levels above 0.1 mg/L in surface water and effluents from gas, condensate and oil platform operations.

Methodology and Instrumentation

Sample preparation involves liquid–liquid extraction with n-pentane, followed by Florisil cleanup to remove polar species. Analysis uses capillary gas chromatography with a non-polar column and flame ionisation detection. Key parameters include

• Oven program: 35 °C for 5 min, 5 °C/min to 100 °C, then 15 °C/min to 340 °C (5 min)
• AC TPI inlet: programmable ramp from 100 °C to 300 °C to prevent discrimination
• Column: 15 m × 0.53 mm ID × 0.15 µm film thickness
• Carrier gas: helium at 7.3 mL/min in constant flow mode
• Injection: automated fast injection of 1.0 µL
• Detector: FID at 320 °C

The temperature-programmable inlet ensures consistent recovery of high-boiling compounds, meeting the C40/C20 peak area ratio requirement (≥ 0.8).

Main Results and Discussion

Chromatograms exhibit clear separation of hydrocarbon peaks from n-heptane to n-tetracontane. Total peak area quantifies dispersed mineral oil, and optional subtraction of toluene, ethylbenzene and xylene isomer peaks refines aromatic reporting. A custom report template automates results in compliance with ISO 9377-2 and DIN H53.

Benefits and Practical Applications

This turnkey GC solution offers high accuracy, reproducibility and minimal inlet discrimination, supporting routine environmental surveillance, industrial effluent testing and quality assurance in petroleum and petrochemical sectors. Automated standby mode reduces gas consumption and prolongs instrument conditioning.

Future Trends and Possibilities

Advances may include coupling GC with mass spectrometry for enhanced speciation, development of portable GC systems for field deployment, integration of real-time monitoring networks, and further inlet technology innovations to capture ultra-light hydrocarbon fractions.

Conclusion

The extended hydrocarbon oil index method delivers a robust, standardized approach for measuring dispersed mineral oil in water. The combination of AC TPI inlet, optimized column choice and dedicated software provides laboratories with a comprehensive, compliant solution.

Reference

AC Analytical Controls, Extended Hydrocarbon Oil Index according to ISO 9377-2 and DIN H53 by Gas Chromatography, PAC L.P. Application Note 00.00.113, 2011.