Hydrocarbon Oil Index Determination in Water Using a Simple, Cost-Effective System

Significance of Hydrocarbon Oil Index Determination

Hydrocarbon pollution in aquatic environments poses ecological and health risks, necessitating reliable monitoring techniques.
The Hydrocarbon Oil Index quantifies total hydrocarbons from C10 to C40, supporting compliance with environmental regulations.

Objectives and Study Overview

This work demonstrates a streamlined, cost-effective protocol for determining hydrocarbon oil index in water via GC-FID.
Key goals include minimizing analysis time, ensuring uniform response across chain lengths, and automating sample throughput.

Methodology and Instrumentation

A Thermo Scientific TRACE 1310 GC equipped with a programmed temperature vaporizing injector and instant-connect FID module was employed to reduce discrimination between light and heavy hydrocarbons.
An AI/AS 1310 autosampler managed sample introduction, while Chromeleon 7.2 CDS software controlled data acquisition and processing.

• Gas chromatograph: Thermo Scientific TRACE 1310 GC
• Column: Thermo Scientific TG-5, 15 m × 0.25 mm, 0.25 μm film thickness
• Carrier gas: Helium at 4 mL/min constant flow
• Injection: 1 µL split mode (20:1), PTV ramp 50 °C to 350 °C
• Oven program: 40 °C (0.5 min), 50 °C/min to 350 °C (1.3 min hold)
• Detector: FID at 350 °C

Sample extraction and cleanup followed EN ISO 9377-2 guidelines (not detailed here).

Main Results and Discussion

A seven-point calibration (0–1 mg/mL) showed linearity with r² = 0.99 for C10–C40 hydrocarbons.
Discrimination tests with a Florida hydrocarbon mix yielded a C40/C20 response ratio above 0.8, confirming negligible bias across chain lengths.
Reproducibility over seven injections delivered relative standard deviations below 2.3% for all target compounds.
Blank injections following high-concentration samples revealed minimal carryover, ensuring data integrity.

Benefits and Practical Applications

• Run time under 10 minutes enhances laboratory throughput.
• PTV injector ensures consistent sensitivity for light and heavy hydrocarbons.
• Automated sampling (155 positions) supports high-volume environmental monitoring and QA/QC workflows.
• Chromeleon CDS enables customizable reporting aligned with regulatory calculations.

Future Trends and Applications

Integration of mass spectrometric detection could provide compound-specific identification and lower detection limits.
Portable GC-FID systems may allow on-site hydrocarbon screening in remote locations.
AI-driven data analysis could advance pattern recognition and contaminant source attribution.

Conclusion

The described GC-FID method, featuring a PTV injector and automated sampling, achieves rapid, reproducible, and discrimination-free quantification of hydrocarbon oil index in water.
This approach meets regulatory criteria while offering operational efficiency for environmental laboratories.

Reference

• EN ISO 9377-2 Water quality—Determination of hydrocarbon oil index—Part 2: Method using gas chromatography