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

Importance of the Topic

Hydrocarbon pollutants such as total oil and grease (TOG) and total petroleum hydrocarbons (TPH) in water can harm aquatic ecosystems and human health. Reliable, sensitive, and environmentally friendly analytical methods are essential to monitor these contaminants and support regulatory compliance.

Objectives and Overview

This study demonstrates the application of a Fourier transform infrared (FTIR) spectrometer, IRXross, combined with LabSolutions IR software in quantitation mode to measure TOG and TPH in water samples. The procedure follows ASTM D7678-17, using cyclohexane for solvent extraction and tetradecane as the calibration standard.

Methodology and Instrumentation

Sample Preparation

• Acidify 450 mL environmental water sample with hydrochloric acid.
• Extract hydrocarbons with 25 mL cyclohexane and measure extract directly for TOG.
• Filter extract through sodium sulfate and Fluorisil to remove water and polar compounds; measure filtrate for TPH.

Calibration

• Prepare stock solution of 18 000 mg/L tetradecane in cyclohexane.
• Generate standards from 18 to 1 800 mg/L; apply enrichment factor (450 mL/25 mL = 18) to report equivalent oil concentrations in water.

Used Instrumentation

IRXross FTIR spectrometer with:

• Specac Omni-Cell liquid cell (1 mm path length, CaF2 windows).
• DLATGS detector; spectral resolution 8 cm−1; accumulation 45 scans; Square-Triangle apodization.

Results and Discussion

Calibration of tetradecane in cyclohexane showed excellent linearity (r2 > 0.999) based on peak height at 1 377 cm−1. Method validation using a 10 mg/L spike yielded 100.2 % recovery and RSD of 3.08 %, confirming accuracy and precision. Analysis of a seawater sample produced 4.92 mg/L TPH and 4.65 mg/L TOG, demonstrating consistent performance for environmental monitoring.

Benefits and Practical Applications

• High sensitivity to low hydrocarbon concentrations in water.
• Use of cyclohexane offers a safer, more environmentally friendly solvent compared to halogenated alternatives.
• Direct FTIR measurement reduces analysis time and solvent consumption.

Future Trends and Opportunities

Advancements may include field-deployable FTIR systems for on-site testing, automated extraction workflows, integration with chemometric data analysis, and extension of the approach to other environmental matrices such as soil and sludge.

Conclusion

The IRXross FTIR method complies with ASTM D7678-17 and provides accurate, precise, and sensitive determination of TOG and TPH in water. Its adoption can enhance routine monitoring and regulatory compliance while reducing environmental impact.

References

• ISO 9377-2:2000 Water quality – Determination of hydrocarbon oil index – Method using solvent extraction and gas chromatography
• 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