High Sensitivity Measurement of Ultra-Trace Amount of Silicone Oil by IRXross

Importance of the Topic

The precise detection and quantification of ultra-trace levels of silicone oil are essential in quality control, contamination monitoring and research across pharmaceutical, food and materials industries. Conventional transmission FTIR methods often struggle with solvent interference and sensitivity limits when dealing with minute amounts of analyte dissolved in volatile solvents.

Objectives and Study Overview

This study demonstrates a high-sensitivity quantitative protocol for measuring trace amounts of polydimethylsiloxane (PDMS) dissolved in n-hexane using the newly released Shimadzu IRXross FTIR. Key aims were to overcome spectral masking by the solvent and to establish a reliable calibration for PDMS concentrations down to 1 ppm.

Methodology and Instrumentation

Methodology:

• Initial transmission measurements with a 0.1 mm KBr liquid cell failed to distinguish PDMS peaks at 100 ppm due to overlapping n-hexane absorption.
• Condensation ATR approach: 20 μL of sample solution dripped onto an ATR prism, followed by solvent evaporation, leaving PDMS residue for measurement.
• Use of a 9-reflection diamond ATR accessory enhanced sensitivity versus single-reflection ATR.
• Quantification based on height of the 1260 cm⁻¹ PDMS peak after baseline correction.

Instrumentation:

• FTIR Spectrometer: Shimadzu IRXross with high-stability interferometer (same as IRTracer-100)
• ATR Accessory: MicromATR 9-reflection diamond disk
• Measurement Settings: resolution 4 cm⁻¹, 100 scan accumulations, SqrTriangle apodization, DLATGS detector

Results and Discussion

Condensation ATR enabled clear observation of PDMS absorption bands at ~1260 cm⁻¹ and ~1100 cm⁻¹ as n-hexane peaks diminished over evaporation time. Calibration across 1–250 ppm PDMS yielded a linear response with r² ≥ 0.999. The 9-reflection ATR configuration achieved detection down to 1 ppm, demonstrating a significant sensitivity improvement over transmission methods and single-reflection ATR.

Benefits and Practical Applications

• Elimination of solvent spectral interference through condensation ATR improves selectivity.
• High signal-to-noise ratio of IRXross supports detection of extremely weak absorption features.
• Quantitative trace analysis of silicones and other non-polar contaminants in volatile matrices.
• Potential application in routine QA/QC, environmental screening and process monitoring.

Future Trends and Applications

Advances may include integration of automated sample deposition and evaporation control for higher throughput, extension to other volatile solvent systems, on-line monitoring capabilities in industrial processes and miniaturized ATR sensors for field analysis. Combining IRXross sensitivity with chemometric tools could further enhance trace quantitation in complex matrices.

Conclusion

The IRXross FTIR, coupled with a condensation and multi-reflection ATR approach, provides a robust and sensitive method for quantitative analysis of ultra-trace silicone oils in volatile solvents. The protocol achieves reliable detection down to 1 ppm PDMS with excellent linearity, offering a practical solution for contamination control and trace analysis in various analytical laboratories.

Reference

• Maruyama K. High Sensitivity Measurement of Ultra-Trace Amount of Silicone Oil by IRXross. Shimadzu Application News, First Edition May 2022.