DialPath Sampling Accessory

Significance of the Topic

Accurate transmission FTIR measurements of liquids are essential in analytical chemistry for both qualitative and quantitative analyses across industries from pharmaceuticals to petrochemicals. Traditional demountable or flow cells often suffer from inconsistent pathlengths, sample loss, and time-intensive cleaning, creating a need for a robust, reproducible sampling approach.

Objectives and Study Overview

This document introduces the DialPath sampling accessory for Agilent FTIR systems, aiming to simplify transmission measurements of liquid and thin film samples. It outlines the accessory’s design to provide fixed pathlengths, accommodate varying sample viscosities, and eliminate the drawbacks of conventional cells.

Methodology and Instrumentation

The DialPath operates by placing a small droplet of liquid or a polymer film on a window, then rotating the accessory to select one of three preset pathlengths (30, 50, 100 µm or 50, 100, 200 µm) with ±0.25 µm repeatability. Sample windows are easily cleaned between analyses and a validation step ensures no residue remains. The FTIR measurements cover the spectral range 5100 to 600 cm-1.

Used Instrumentation

• Agilent Cary 630 FTIR with interchangeable DialPath module
• Agilent 4500 and 5500 Series Compact FTIR with fixed DialPath accessory
• Optional TumblIR accessory for single fixed pathlength between 100 and 1000 µm
• ZnSe windows optimized for high throughput in humid environments

Main Results and Discussion

The DialPath accessory demonstrated highly reproducible, contamination-free transmission measurements without sample dilution or cell assembly variability. Case studies include:

• Comparison with ATR and cell-based methods for food, drug, and cosmetic additives showing comparable qualitative and quantitative performance.
• Analysis of volatile liquids, confirming minimal evaporation loss during measurement.
• On-site screening of bovine milk adulterants with detection limits down to 3 % v/v.
• Determination of biodiesel (FAME) in marine diesel fuel and phenolic antioxidants (DBPC and DBP) in insulating oils according to ASTM and IEC standards.
• Quantification of simethicone in pharmaceuticals, matching or exceeding traditional cell results while reducing cost and analysis time.

Benefits and Practical Applications

The DialPath enhances analytical workflows by offering fixed, repeatable pathlengths that handle multiple peak intensities in a single run. It reduces sample handling time, avoids bubble formation, and requires minimal cleaning. Applications span polymer film analysis, quality control in food and dairy, environmental monitoring, fuel testing, and pharmaceutical assays.

Future Trends and Potential Applications

Future developments may include:

• Expanded custom pathlength options up to 1000 µm for diverse sample matrices.
• Integration with portable FTIR instruments for field-based environmental and industrial monitoring.
• Coupling with advanced chemometric software for real-time data analysis.
• Micro-volume and automated sampling adaptations for high-throughput laboratories.

Conclusion

The DialPath accessory provides a streamlined, reliable solution for transmission FTIR measurements of liquids and thin films. Its fixed pathlength design, ease of cleaning, and compatibility with multiple Agilent FTIR platforms make it an attractive tool for analytical chemists requiring reproducible and efficient workflows.

Reference

• Agilent Technologies, Inc. DialPath Sampling Accessory Technical Overview, 2021.