Quantitative measurement of active pharmaceutical ingredients using the diffuse reflectance Cary 630 FTIR

Significance of the Topic

The quantitative analysis of active pharmaceutical ingredients in solid formulations is critical for quality control and regulatory compliance. Diffuse reflectance FTIR offers a rapid, non-destructive alternative to conventional pellet techniques, reducing sample preparation complexity and enhancing throughput in pharmaceutical laboratories.

Objectives and Study Overview

This application note investigates the use of diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) with the Agilent Cary 630 FTIR to measure acetaminophen concentration in a corn starch matrix. Two sample preparation approaches are compared: direct measurement of neat powders and dilution in potassium bromide (KBr). Calibration models are developed and evaluated for linearity and precision.

Methodology and Instrumentation

Samples of acetaminophen mixed with corn starch at 0 to 10 wt% were divided into two sets. One set was blended with dry KBr at a 1:10 ratio prior to measurement; the other was analyzed neat. All spectra were acquired on the Agilent Cary 630 FTIR equipped with a diffuse reflectance adapter using 74 scans over 30 seconds at 4 cm-1 resolution. Data collection employed MicroLab PC software, and quantitative calibrations were processed in Agilent Resolutions Pro.

• Agilent Cary 630 FTIR spectrometer
• Diffuse reflectance sampling interface
• MicroLab PC software
• Agilent Resolutions Pro software

Results and Discussion

Diluted samples produced absorbances of 0.6–0.8 AU at the 1559 cm-1 acetaminophen band, ratioed to the 1379 cm-1 corn starch reference. This calibration yielded an R2 of 0.999. Neat samples were calibrated using the 1559 cm-1 band area against a corn starch overtone near 2100 cm-1, achieving an R2 of 1.000. Both approaches demonstrated excellent linearity, with neat analysis avoiding pellet preparation and dilution providing optimized signal levels for high-concentration samples.

Benefits and Practical Applications

Diffuse reflectance FTIR eliminates the need for time-consuming KBr pellet preparation while maintaining quantitative accuracy. The Cary 630 FTIR platform supports quick switching between DRIFT for solids and ATR or DialPath for liquids, making it versatile for pharmaceutical R&D, QA/QC, and method development.

Future Trends and Opportunities

Advancements in detector technology and multivariate data analysis will further enhance sensitivity and robustness of DRIFT methods. Integration with automated sampling and machine learning algorithms could enable real-time monitoring of solid formulations during manufacturing processes.

Conclusion

The Agilent Cary 630 FTIR with diffuse reflectance sampling provides a reliable, efficient solution for quantitative analysis of pharmaceutical solids. Both diluted and neat measurement modes deliver high linearity and precision, streamlining workflow in pharmaceutical laboratories.

Reference

Higgins F and Seelenbinder J. Quantitative measurement of active pharmaceutical ingredients using the diffuse reflectance Cary 630 FTIR. Agilent Technologies Application Note 5990-9414EN, 2011.