Extraction of Total Petroleum Hydrocarbons (TPH) from Soil Using Supercritical Fluids

Importance of Topic

Soil contamination by petroleum hydrocarbons from leaking underground storage tanks poses a significant threat to groundwater quality and ecosystem health. Rapid, reliable quantification of Total Petroleum Hydrocarbons (TPH) is essential for environmental monitoring, regulatory compliance, and effective remediation strategies. Supercritical Fluid Extraction (SFE) using carbon dioxide offers a greener, efficient alternative to traditional solvent-based methods, reducing organic solvent consumption and improving extraction selectivity.

Objectives and Study Overview

This application note describes the implementation of EPA Method 3560 for SFE of TPH from soil. It outlines the workflow, extraction parameters, collection approaches, and analytical pathways to support environmental laboratories in adopting SFE for routine petrochemical contamination assessment.

Methodology and Instrumentation

The procedure utilizes Applied Separations’ Spe-ed™ Supercritical Fluid Extraction system equipped with the following:

• Spe-ed™ SFE system with oven and pressure control
• Spe-ed Matrix (diatomaceous earth) as dispersant
• Supercritical CO2 (SFC/SFE grade)
• C18/18% SPE cartridges (1 g/6 mL) or tetrachloroethylene collection solvent
• Drying agents (anhydrous magnesium sulfate or diatomaceous earth) for high-moisture samples

Extraction procedure:

• Weigh 3 g of soil; if moisture exceeds 20 %, mix with drying agent at a 1:1 ratio to improve porosity.
• Transfer the mixture into a 10–24 mL extraction vessel, secure with silanized glass wool plugs, and fill void volume with Spe-ed Matrix.
• Set extraction conditions: 5000 psi, 80 °C, CO2 flow 1 L/min dynamic for 30 minutes.
• Collect extracts either on a C18 SPE cartridge or in a 3 mL tetrachloroethylene trap.
• Analyze tetrachloroethylene extracts by EPA infrared methods 8440 or 8840. For C18 cartridges, elute with tetrachloroethylene for infrared analysis or with methylene chloride for non-halogenated volatile organic analysis by EPA Method 8015 GC-FID.

Main Results and Discussion

SFE with CO2 demonstrated consistent and efficient recovery of TPH across diverse soil matrices. The method’s use of moderate temperature and pressure conditions preserves analyte integrity while minimizing co-extraction of interferences. Inline SPE cartridges streamline cleanup, yielding reproducible results with minimal post-extraction handling.

Benefits and Practical Applications

• Meets EPA Method 3560 requirements for regulatory TPH monitoring.
• Reduces organic solvent use and waste disposal costs.
• Short extraction times (30 min) support high-throughput processing.
• Adaptable to soils, sediments, and fly ash matrices.

Future Trends and Potential Uses

Emerging developments in SFE include direct coupling with supercritical fluid chromatography (SFC) and mass spectrometry for compound-specific hydrocarbon profiling. The design of compact, field-deployable SFE units may enable on-site sample preparation and rapid decision-making in environmental remediation projects. Exploration of alternative green solvents and automated workflows will further enhance method efficiency and sustainability.

Conclusion

Supercritical CO2 extraction of TPH, as approved by EPA Method 3560, provides a robust, environmentally friendly approach for soil contamination analysis. Its regulatory alignment, operational efficiency, and reduced solvent footprint make it an attractive solution for environmental laboratories and remediation practitioners.

Reference

EPA Method 3560 Supercritical Fluid Extraction