Assessment of diffuse transmission and reflection modes in near-infrared quantification, part 2: DIFFuse reflection...

Area of Science:

• Pharmaceutical manufacturing
• Analytical chemistry
• Spectroscopy

Background:

• Near-infrared (NIR) spectroscopy is a rapid, nondestructive analytical technique.
• Key applications include content uniformity and process analytics in pharmaceutical manufacturing.
• Understanding diffuse reflection (DR) information depth is crucial for accurate analysis.

Purpose of the Study:

• To assess the information depth of diffuse reflection (DR) in near-infrared spectroscopy for pharmaceutical tablets.
• To evaluate the impact of sample thickness and coating on DR spectral analysis.
• To compare the utility of DR versus diffuse transmission for tablet analysis.

Main Methods:

• Experiments involved varying tablet thicknesses (MCC tablets), double-layered tablets (MCC/phenylbutazone), and incremental film coatings.
• Diffuse reflection (DR) information depth was analyzed using incremental thickness and cluster analysis.
• Signal drop analysis was performed on coated tablets to determine information content at different depths.

Main Results:

• DR information depth for pharmaceutical tablets was found to be less than 0.5 mm.
• A 50% signal drop occurred at 0.05–0.07 mm with incremental coating, and a 90% signal drop (10% information) was observed between 0.20–0.25 mm.
• NIR DR primarily analyzes surface information, with limited penetration through coatings.

Conclusions:

• Diffuse reflection (DR) mode in NIR spectroscopy is best suited for analyzing the very surface of pharmaceutical tablets.
• DR mode is less effective than diffuse transmission for analyzing the core content of thick-coated, multilayer, or inhomogeneous tablets.
• The limited information depth of DR restricts its use for quantitative analysis beyond thin surface layers.