Dual injection for Hydrocarbon Oil Index (HOI) determination in water and soil with helium carrier gas conservation

Importance of the Topic

Petroleum hydrocarbons are widespread environmental contaminants that accumulate in water and soil, posing risks to ecosystems and public health. Monitoring the Hydrocarbon Oil Index (HOI), also known as Total Petroleum Hydrocarbon (TPH), is a regulatory requirement in many countries to ensure compliance with water and soil quality standards. Accurate, high‐throughput methods are essential to support routine environmental testing, minimize costs, and reduce analysis times without sacrificing data integrity.

Objectives and Study Overview

This study aimed to demonstrate a cost‐effective, high‐throughput gas chromatography–flame ionization detection (GC‐FID) approach for quantifying HOI/TPH in aqueous and soil matrices. By implementing a dual‐injection, Gemini autosampler configuration combined with carrier‐gas saving technology, the method seeks to double sample throughput, lower helium consumption, and maintain compliance with international standards (U.S. EPA, ISO, ISPRA).

Methodology

Sample preparation followed official protocols involving solvent extraction and Florisil clean‐up:

• Water: 1 L samples extracted with nonpolar solvent, Florisil clean‐up, concentration to 1 mL.
• Soil: 5 g dry weight extracted via accelerated solvent extraction or sonication, Florisil clean‐up, concentration to 10 mL.

Chromatographic separation used a TraceGOLD TG-Mineral Oil column (15 m × 0.32 mm × 0.15 µm) and a TRACE 1610 GC under the following conditions:

• Injection: 1–2 µL splitless mode, baseline integration from n-decane (C10) to n-tetracontane (C40) for water (C12–C40 for soil).
• Oven program: 50 °C to 360 °C in five ramps, total run time ≈7.24 min.
• Carrier gas: helium at 4.0 mL/min, with HeSaver-H2Safer technology to switch split and purge flows to nitrogen or argon.

Instrumentation Used

• Thermo Scientific TRACE 1610 GC
• AI/AS 1610 autosamplers in Gemini dual‐tower configuration (310‐vial capacity)
• iConnect split/splitless injectors and FIDs, upgraded for HeSaver-H2Safer mode
• Chromeleon 7.3 Chromatography Data System for acquisition, processing, and secure reporting

Main Results and Discussion

Blank injections confirmed a clean baseline critical for low‐level TPH detection. Key performance metrics included:

• Recovery: C40/C20 peak‐area ratios consistently above 90%, exceeding the 80% regulatory requirement.
• Repeatability: six injections of n-alkane mix at 25 µg/mL yielded <1% RSD in peak areas and <0.05% RSD in retention times.
• Robustness: in a sequence of 278 injections (including standards, QCs, and 200 soil samples), QC RSDs were ≤3% without maintenance downtime.
• Linearity: nine‐level calibration from 5 to 2,000 µg/mL returned R² > 0.999; lower limit extended to 2 µg/mL with 2 µL injection, maintaining <10% deviation.
• Gas savings: HeSaver-H2Safer mode increased helium cylinder life by 4.5× under continuous operation, reducing carrier‐gas cost.

Benefits and Practical Applications

Implementing this dual‐injection GC‐FID approach delivers:

• Up to 2× sample throughput without hardware reconfiguration.
• Significant helium savings and lower operating costs.
• Compliance with EPA, ISO, and ISPRA standards for water and soil HOI/TPH analysis.
• Automated data handling and reporting to meet modern data‐integrity guidelines.

Future Trends and Potential Applications

Advances likely to shape TPH analysis include:

• Broader adoption of hydrogen carrier gas with smart gas‐saving hardware.
• Integration of automated sample preparation platforms to further boost throughput.
• Miniaturized GC systems for on-site monitoring and rapid decision‐making.
• Enhanced data analytics and AI-driven quality control within CDS environments.

Conclusion

The dual‐injection Gemini configuration with HeSaver-H2Safer technology on the TRACE 1610 GC offers a robust, compliant, and efficient solution for TPH determination in water and soil. It achieves high recovery, precision, and linearity while doubling throughput and significantly reducing helium consumption, meeting the requirements of environmental testing laboratories.

Reference

1. ATSDR. Public Health Statement for Total Petroleum Hydrocarbons (TPH), U.S. Department of Health and Human Services.
2. U.S. EPA. Method 8015C: Nonhalogenated Organics Using GC/FID, Revision 4, 2003.
3. ISO 16703:2011. Soil Quality – Determination of Hydrocarbons in the C10–C40 Range by GC.
4. ISO 14039:2004. Characterization of Waste – Hydrocarbon Content C10–C40 by GC.
5. ISO 9377-2:2000. Water Quality – Hydrocarbon Oil Index by Solvent Extraction and GC.
6. ISPRA Doc. 46/14. Determination of Total Hydrocarbons in Water, 2014.
7. ISPRA Doc. 04/11. Analysis of Hydrocarbons > C12 in Contaminated Soils, 2011.
8. Thermo Fisher Scientific TN 74104. Doubling Throughput with AI/AS 1610 Gemini Configuration.
9. Thermo Fisher Scientific TN 001218. GC Carrier Gas Conservation with HeSaver-H2Safer Technology.
10. Thermo Fisher Scientific. Helium Saver Calculator (online application).