FTIR transmission measurement of volatile liquids using the Cary 630 FTIR equipped with DialPath technology

Importance of the Topic

The reliable quantification of volatile liquids by infrared spectroscopy underpins quality control in fuels, specialty chemicals and pharmaceuticals. Traditional sealed transmission cells demand meticulous handling to avoid air bubbles and damage, limiting throughput and accessibility. The introduction of an open transmission accessory that tolerates volatility and simplifies sample loading addresses a longstanding bottleneck in liquid FTIR analysis.

Study Objectives and Overview

This application note evaluates the performance of Agilent’s Cary 630 FTIR spectrometer equipped with DialPath technology for rapid transmission measurements of volatile solvents and analytes. Two model systems are studied:

• Dioctyl phthalate in tetrahydrofuran (nonvolatile solute in volatile solvent)
• Benzene in hexane (volatile solute in volatile solvent)

Key goals include assessing evaporation effects during measurement and demonstrating quantitative accuracy under typical lab conditions.

Methodology and Instrumentation

The Cary 630 FTIR instrument, fitted with the DialPath accessory, offers interchangeable fixed pathlengths (50, 100, 250 µm) selectable by a simple dial. Sample loading requires less than 250 µL of liquid, with only 3 µL in the infrared beam’s active region. Rapid scan speed (148 scans in ~60 s at 4 cm⁻¹ resolution) minimizes diffusion or evaporation artifacts. Quantitative models were built using partial least squares (PLS) regression on characteristic absorption bands.

Main Results and Discussion

For the dioctyl phthalate—THF system, volumetric standards (0–5 % DOP) scanned in triplicate (64 scans at 8 cm⁻¹) yielded a cross-validation error of 0.012 % DOP and R²=0.9999. Time-delay tests (0–120 s between loading and measurement) revealed deviations within ±2 % relative error, confirming negligible solvent loss even after two minutes.

In the benzene—hexane experiment, a PLS model achieved a validation error of 0.0076 % benzene with R²=0.9960. Repeat measurements on a 0.5 % benzene sample at delays up to 60 s remained accurate within ±2 % relative error. These data demonstrate that the small active region and fast acquirement preclude significant volatility effects during routine scans.

Practical Benefits and Applications

• Rapid, user-friendly analysis of volatile or viscous liquids without syringes or fragile cells.
• Elimination of sealing steps reduces training requirements and sample handling errors.
• High throughput screening in QA/QC labs for fuels, solvents, reaction monitoring or extraction processes.

Future Trends and Potential Applications

Emerging needs in inline process control and miniaturized analytics may leverage open-cell FTIR designs for real-time monitoring of chemical reactions and solvent purification. Integration with automated sample changers and cloud-based chemometric platforms could further enhance throughput and data accessibility in regulated environments.

Conclusion

The Cary 630 FTIR with DialPath accessory delivers robust, accurate transmission measurements of volatile liquid mixtures in under one minute, with minimal evaporation or diffusion artifacts. Its open-cell design and rapid scan capability simplify quantitative and qualitative analyses, offering a compelling solution for modern laboratory workflows.

Reference

Higgins F, Rein A. FTIR transmission measurement of volatile liquids using the Cary 630 FTIR equipped with DialPath technology. Agilent Technologies Application Note 5990-8540EN. 2011.