Measuring Hydrocarbon Oil Index according to ISO 9377-2 (DIN H53)

Importance of the Topic

The Hydrocarbon Oil Index (HOI) quantifies the total amount of non-polar extractable hydrocarbons in water samples. Accurate HOI measurement under ISO 9377-2 and DIN H53 is vital for environmental monitoring, drinking water quality assessment and wastewater treatment control. Standardized HOI analysis supports regulatory compliance and risk assessment in industrial and municipal settings.

Objectives and Study Overview

This study presents a gas chromatography method developed by Agilent Technologies to determine HOI in potable, surface and wastewater matrices. The approach meets ISO 9377-2 and DIN H53 requirements, enabling quantification of HOI at concentrations above 0.1 mg/L. Key goals included method robustness, ease of implementation and reliable discrimination of low- and high-boiling hydrocarbons.

Methodology and Instrumentation

Sample Extraction

• Non-polar solvent selected with boiling point 39 °C–69 °C replaces halogenated solvents for environmental and safety benefits.
• Target compounds elute between n-decane (C10) and n-tetracontane (C40) without adsorption on Florisil.

Gas Chromatography Setup

• Instruments: Agilent 6890 or 6850 GC with Split/Splitless inlet and Flame Ionisation Detector (FID).
• Column: 15 m × 0.53 mm × 0.15 µm HP-1 capillary column (Agilent Part No. 19095Z-221E).
• Inlet Liner: Proprietary injection port liner (Agilent Part No. 5183-4647) for reduced discrimination and maintenance.
• Carrier Gas: Helium at 7.4 mL/min constant flow.
• Temperature Program: Isothermal 35 °C (1.5 min), ramp 5 °C/min to 60 °C, then 15 °C/min to 350 °C (5 min hold).
• Injection: Automated fast injection (1 µL) in splitless mode at 375 °C.

Data Handling

• Agilent GC ChemStation software performs background subtraction, column bleed correction and custom ISO-compliant reporting.

Main Results and Discussion

Calibration curves generated with hydrocarbon standards exhibited excellent linearity (correlation coefficient ≥ 0.999) over the tested concentration range. A discrimination test involving 25 sequential injections of decane (C10) and tetracontane (C40) confirmed minimal bias between low- and high-boiling compounds, meeting ISO criteria. Background-subtracted chromatograms demonstrated clean baselines and reproducible retention times.

Benefits and Practical Applications

This GC-FID method offers several advantages: robust performance with minimal maintenance, streamlined sample analysis through automated injection and data processing, and full compliance with international HOI regulations. It is well suited for routine quality control in environmental laboratories, water utilities and industrial process monitoring.

Future Trends and Applications

Emerging directions include coupling HOI analysis with mass spectrometry for compound identification, integration with online sampling for real-time monitoring, and further miniaturization of extraction techniques. Advances in software algorithms and machine learning may enhance peak deconvolution and automate regulatory reporting.

Conclusion

The presented GC-FID method delivers a reliable, standardized approach for measuring the Hydrocarbon Oil Index in various water matrices. By adhering to ISO 9377-2 and DIN H53, it ensures regulatory compliance and operational efficiency in environmental and industrial laboratories.