Environmentally friendly oil in water analysis by FTIR spectroscopy, based on ASTM D7678-11

Importance of the Topic

Oil in water monitoring is essential for environmental protection and regulatory compliance in industries such as oil depots, refineries, and offshore platforms. The ability to measure trace oil concentrations on site supports rapid decision making and reduces environmental risks.

Study Objectives and Overview

This work implements the ASTM D7678-11 method using Fourier transform infrared spectroscopy for direct quantification of oil in water. The method replaces ozone-depleting solvents with cyclohexane, enabling sensitive detection (LOD 0.25 mg/L, LOQ 0.75 mg/L) up to 1000 mg/L.

Methodology and Instrumentation

The analytical procedure involves:

• Liquid–liquid extraction of a 900 mL water sample with 20 mL cyclohexane
• Layer separation and removal of the cyclohexane phase
• Drying with sodium sulfate and cleanup on Florisil
• Filtration through a 0.45 μm nylon filter
• FTIR measurement of the methyl bending absorbance at 1378 cm-1

Used Instrumentation

Measurements were performed on Agilent 4500 and 5500 Series portable FTIR spectrometers equipped with either the DialPath or TumblIR 1000 μm liquid cells.

Main Results and Discussion

An 11-level calibration of mineral oil in cyclohexane demonstrated excellent linearity (R2 = 0.99929) over the target range. Validation with high (9.3 mg/L) and low (1.4 mg/L) standards yielded recoveries of 101.7% and 103.2%, with relative standard deviations of 2.69% and 5.69%, respectively. The method correlates well with existing ASTM, ISO, and EPA protocols and outperforms prior FTIR approaches in cost and environmental impact.

Benefits and Practical Applications

This FTIR method offers:

• A non-halogenated solvent that is safer and more sustainable
• Cost savings of over 90% per analysis compared to traditional halogenated methods
• Rapid, on-site testing capability with minimal sample preparation
• Compatibility with automated multivariate data analysis software

Future Trends and Opportunities

Advancements may include integration with remote sensing platforms, further miniaturization of FTIR devices, and enhanced multivariate calibration models to extend applicability to complex matrices and ultra-trace detection.

Conclusion

The cyclohexane-based FTIR method adhering to ASTM D7678-11 provides a reliable, eco-friendly, and cost-effective solution for monitoring oil in water, meeting stringent regulatory requirements with high accuracy, portability, and ease of use.