Solvent-Free Determination of Oil and Grease in Water Following ASTM D7575

Significance of the topic

Accurate determination of oil and grease (O&G) in water is central to environmental compliance, industrial process control, and public health protection. Traditional solvent-based extraction methods present safety, health, environmental, and operational burdens (for example, use of CFCs historically and n-hexane under EPA Method 1664). ASTM D7575 provides a solvent-free alternative that reduces hazardous waste and simplifies field and laboratory workflows while maintaining regulatory-grade quantitative performance.

Objectives and study overview

This application note documents a validated, solvent-free workflow for determining recoverable oil and grease in water following ASTM D7575. The study demonstrates the combined performance of Orono Spectral Solutions (OSS) ClearShot membrane extraction and the Agilent Cary 635 FTIR spectrometer with Agilent MicroLab software. Primary aims were to verify quantitative accuracy, linearity, reproducibility, and operational advantages across a practical concentration range (~5–200 mg/L, ppm).

Methodology

1. Extraction: Single-use OSS ClearShot membranes were used to filter and concentrate hydrocarbons directly from homogenized water samples.
2. Drying and mounting: Membranes were briefly air-dried, placed into an OSS extractor holding card and loaded into the Cary 635 transmission module.
3. FTIR measurement: Spectra were recorded and the peak height at 2,920 cm–1 (aliphatic C–H stretching) was measured using a Dual Baseline approach.
4. Quantitation: MicroLab software applied a calibration curve to convert peak height to oil-in-water concentration (mg/L) and presented color-coded results based on user thresholds; reports and data export were available.
5. Verification: Seven independently prepared samples spanning ~5–200 ppm O&G were processed to evaluate accuracy, linearity, and reproducibility.

Used instrumentation

• Agilent Cary 635 FTIR spectrometer with transmission module.
• Agilent MicroLab software with an OSS macro and picture-driven workflow.
• Orono Spectral Solutions (OSS) ClearShot single-use membrane extractors and extractor holding card.

Main results and discussion

Verification across seven independently prepared samples showed close agreement between measured and known O&G concentrations over the tested range. The FTIR response (peak height at 2,920 cm–1) correlated linearly with hydrocarbon mass on the membrane, yielding a calibration with R² > 0.99. Key performance observations:

• Quantitative accuracy from approximately 5 to 200 ppm, with no systematic bias at either end of the range.
• High reproducibility and analytical sensitivity adequate for regulatory reporting and process monitoring.
• Rapid spectral acquisition (seconds per membrane) and automated result calculation reduced operator intervention and training needs.

Benefits and practical applications

The integrated OSS + Agilent workflow provides several practical advantages over legacy solvent-based methods:

• Solvent-free operation eliminates the purchase, storage, handling, and disposal of hazardous organic solvents (e.g., n-hexane or historical CFCs), reducing health and safety risks and environmental footprint.
• Faster and simpler sample preparation and analysis enable at-line or field-capable testing, supporting operational decision-making and compliance monitoring.
• Lower operating costs by removing solvent-related expenses and hazardous waste management.
• Compact, portable instrumentation and picture-driven software simplify deployment across laboratories, treatment plants, and field teams.

Future trends and potential uses

Solvent-free membrane extraction combined with compact FTIR detection aligns with broader trends toward greener analytical workflows and decentralised environmental monitoring. Anticipated developments and opportunities include:

• Broader adoption for routine regulatory monitoring and industrial effluent screening to replace solvent-based gravimetric methods.
• Integration with on-site sampling programs and automated data pipelines for near-real-time process control.
• Refinement of membrane chemistries and calibration models to extend detection capability to a wider range of hydrocarbon classes or lower detection limits.
• Implementation of standardized macros and automated reporting to support laboratory accreditation and quality management systems.

Conclusion

The OSS ClearShot membrane extraction combined with the Agilent Cary 635 FTIR and MicroLab software provides a validated, solvent-free ASTM D7575 workflow that achieves accurate, linear, and reproducible O&G measurements from ~5 to 200 ppm. The approach reduces health, safety, and environmental risks while improving throughput and enabling field-capable testing—making it a practical replacement for legacy solvent-based methods in many monitoring scenarios.

Reference

1. ASTM International. Standard Test Method for Solvent-Free Membrane Recoverable Oil and Grease by Infrared Determination; ASTM D7575–11(2017); ASTM International, 2017.