Robust and cost-effective analysis of TPH in water and soil using GC-FID

Importance of the Topic

The analysis of total petroleum hydrocarbons (TPH) in environmental samples is essential for monitoring contamination in water and soil, ensuring regulatory compliance, and protecting ecosystems and human health.

Study Goals and Overview

The study aimed to develop a robust, rapid, and cost-effective gas chromatography–flame ionization detection (GC-FID) method for routine determination of TPH in water and soil at a high-throughput laboratory. The approach focused on simple sample preparation, minimal solvent use, and compatibility with common instrumentation.

Methodology

Water samples were processed using solid-phase extraction (SPE) cartridges after methanol addition and pH adjustment, followed by hexane elution and nitrogen-assisted concentration. Soil samples underwent ultrasonic extraction with hexane before concentration. Calibration was performed with mixed diesel/motor oil standards and C8–C40 alkane mixtures over a wide concentration range (1–2000 μg/mL for hydrocarbons C10–C40). Data processing and reporting used a chromatography data system with flexible configuration.

Used Instrumentation

• Thermo Scientific TRACE 1310 GC with PTV splitless inlet
• Thermo Scientific TriPlus RSH autosampler
• Flame ionization detector (FID) with hydrogen carrier gas
• TG-Mineral Oil capillary column (15 m × 0.32 mm × 0.15 μm)
• TurboVap concentrator for extract evaporation

Main Results and Discussion

• Chromatographic separation of alkanes C10–C40 was achieved in under 6 minutes.
• Use of hydrogen as carrier gas reduced analysis time without loss of resolution and lowered operating costs compared to helium.
• Calibration exhibited excellent linearity (R2 > 0.998) and repeatability (residual RSD <6%).
• Instrument detection limit for total TPH (C10–C40) was 0.33 μg on-column, corresponding to <5 mg/kg in soil and <1 μg/L in water.
• Repeatability and robustness tests over 99 injections and five days showed peak area RSD of 5.7% and concentration RSD of 5.3% without maintenance.
• Water sample recoveries for spiked matrices exceeded 115% with RSD <5%, demonstrating method reliability.

Benefits and Practical Applications

The method provides rapid turnaround, low solvent consumption, and high throughput suitable for environmental monitoring, regulatory laboratories, and quality control in water and soil analysis.

Future Trends and Opportunities

Advances may include integration with mass spectrometry for compound identification, miniaturized and field-portable GC-FID systems, use of greener solvents, and automation of sample preparation.

Conclusion

A streamlined GC-FID approach with simple extraction and hydrogen carrier gas offers a reliable, cost-effective solution for TPH analysis in water and soil, combining speed, sensitivity, and robustness for routine environmental testing.

Reference

1. Agency for Toxic Substances & Disease Registry. Toxic Substances Portal Web site: Total Petroleum Hydrocarbons (TPH). Accessed April 13, 2021.
2. BS EN ISO 16703:2011. Soil quality. Determination of hydrocarbon content in the range C10 to C40 by gas chromatography.
3. BS EN ISO 14039:2004. Characterization of waste. Determination of hydrocarbon content in the range of C10 to C40 by gas chromatography.
4. BS EN ISO 9377-2:2000. Water quality. Determination of hydrocarbon oil index using solvent extraction and gas chromatography.
5. ASTM D7678-11. Standard Test Method for Total Petroleum Hydrocarbons in Water and Wastewater with Solvent Extraction using Mid-IR Laser Spectroscopy.
6. Customer Application Note 120, Thermo Fisher Scientific, 2016. Determination of total petroleum hydrocarbons in rubble and soils by accelerated solvent extraction and GC-FID.