Oil in Water Analysis by Solid Phase Extraction

Importance of the Topic

Monitoring oil and grease levels in industrial and wastewater is essential for safeguarding aquatic ecosystems and human health. Regulatory frameworks such as the US Clean Water Act list oil and grease as conventional pollutants that require regular testing. Traditional methods rely on flammable solvents and off-site laboratory analysis, leading to safety hazards, higher costs, and longer turnaround times.

Objectives and Overview

This application note presents a solvent-free alternative based on ASTM D7575, combining solid-phase extraction with transmission FT-IR spectroscopy. The goals are to demonstrate rapid on-site quantification of oil and grease in water, eliminate hazardous solvents, and enable near-real-time feedback for process control.

Methodology and Instrumentation

The ASTM D7575 procedure involves drawing a representative water sample through a membrane extractor, drying the membrane, and acquiring an IR spectrum. Key components:

• FT-IR Spectrometer: Bruker ALPHA II with user-guided operation and optional touch-panel PC for portability.
• Membrane Extractor: OSS ClearShot™ oil and grease extractor housing a membrane compatible with the IR measurement window.
• Calibration and Software: Certified solid-state standards and preconfigured macros automate spectral acquisition, quantification, and reporting based on the ASTM D7575-11 calibration model.

Main Results and Discussion

The combined extraction and measurement workflow delivers results in under 15 minutes per sample, supporting parallel processing for higher throughput. Spectral analysis focuses on the CH2 stretching band near 2920 cm⁻¹, which correlates linearly (R = 1.000) with oil concentration. A detection limit of 1 ppm is achieved for a 10 mL sample using a 25 mm extractor; this limit can be tuned by adjusting sample volume or extractor size. The system also allows automatic library matching to identify oil types, aiding in source tracking of contamination.

Benefits and Practical Applications

Key advantages of this approach include:

• Solvent-free, eliminating explosion and health risks and removing the need for chemical fume hoods.
• On-site operation without sample transport, reducing analysis time and logistics costs.
• Automated calibration and reporting, lowering user expertise requirements and minimizing human error.
• Simultaneous quantification and identification of oil, enabling rapid source attribution in environmental monitoring and industrial maintenance.

Future Trends and Potential Applications

Emerging directions include:

• Integration with portable and handheld FT-IR platforms for field deployment.
• Expanded membrane formats to adapt detection limits and sample matrices (e.g., soil, sludge).
• Automated inline monitoring in process streams for continuous environmental compliance.
• Machine learning algorithms for advanced spectral deconvolution and multi-component oil analysis.

Conclusion

The combination of solid-phase membrane extraction and FT-IR detection under ASTM D7575 offers a fast, accurate, and safe solution for oil and grease analysis in water. By eliminating hazardous solvents and enabling on-site measurement and identification, this method enhances environmental monitoring and industrial quality control while reducing time and operational costs.