Analysis of Total Oil and Grease (TOG) and Total Petroleum Hydrocarbons (TPH) in Water Using FTIR Spectroscopy Based on ASTM D7678-17

Significance of the Topic

The presence of hydrocarbons in water bodies poses serious ecological and human health risks due to persistence and bioaccumulation. Monitoring Total Oil and Grease (TOG) and Total Petroleum Hydrocarbons (TPH) is essential for regulatory compliance, pollution control and safeguarding drinking water.

Objectives and Overview of the Study

This study demonstrates a rapid and sensitive method for quantifying TOG and TPH in water using the Shimadzu IRXross Fourier Transform Infrared spectrometer coupled with LabSolutions IR software. It follows the ASTM D7678-17 standard and employs a cyclohexane extraction protocol to improve safety and environmental compatibility.

Methodology

• Sample Preparation: Acidification of 450 mL water samples, extraction with 25 mL cyclohexane, direct measurement for TOG, followed by filtration through sodium sulfate and Fluorisil for TPH analysis.
• Standard Calibration: Stock solution of tetradecane in cyclohexane (18,000 mg/L) diluted to 18–1,800 mg/L; equivalent water concentrations calculated via an 18-fold enrichment factor.
• FTIR Measurement: Transmission spectra recorded in a Specac Omni-Cell (1 mm path, CaF2 windows) with 8 cm–1 resolution, 45 scans, and SqrTriangle apodization. Quantitation based on peak height at 1,377 cm–1 against a baseline from 1,365 to 1,392 cm–1.

Instrumentation Used

• Shimadzu IRXross FTIR spectrometer
• LabSolutions IR quantitation software
• Specac Omni-Cell liquid cell (CaF2 windows, 1 mm path)
• DLATGS detector

Main Results and Discussion

Calibration curves exhibited excellent linearity with correlation coefficients (r2) above 0.999 across the 1–100 mg/L equivalent range. Method validation using a 10 mg/L spiked standard yielded a mean recovery of 100.2% and RSD of 3.08%, demonstrating high accuracy and precision. Analysis of an environmental seawater sample produced TPH and TOG values of 4.92 mg/L and 4.65 mg/L, respectively, confirming method robustness in real matrices.

Benefits and Practical Applications

• High sensitivity and rapid turnaround for low-level hydrocarbon detection.
• Safer and greener solvent (cyclohexane) compared to halogenated alternatives.
• Direct measurement workflow reduces sample handling and potential loss.
• Applicable for routine environmental monitoring and regulatory compliance.

Future Trends and Potential Applications

Advancements may include integration with automated sample handling, expansion to other extractable contaminants, and coupling with chemometric models for broader hydrocarbon fingerprinting. Portable FTIR platforms could enable on-site screening and real-time water quality assessment.

Conclusion

The IRXross FTIR method based on ASTM D7678-17 provides a reliable, accurate and environmentally friendly approach for quantifying TOG and TPH in water. Its strong linearity, excellent recovery, and operational simplicity make it suitable for diverse laboratory and field applications.

References

1. ISO 9377-2:2000 Water quality – Determination of hydrocarbon oil index; method using solvent extraction and gas chromatography.
2. ASTM D7678-17 Standard Test Method for Total Oil and Grease (TOG) and Total Petroleum Hydrocarbons (TPH) in Water and Wastewater with Solvent Extraction using Mid-IR Laser Spectroscopy.