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  • Title: Investigation on Raman spectral features of a coated tablet under variation of its orientation respective to laser illumination and measurement of nominal coating thickness of packed tablets.
    Author: Kim J, Hwang J, Woo YA, Chung H.
    Journal: J Pharm Biomed Anal; 2016 Nov 30; 131():281-286. PubMed ID: 27611100.
    Abstract:
    To investigate Raman spectral features of a coated biconvex tablet under variation of its orientation respective to laser illumination, spectra of the tablet were collected by illuminating laser on 12 different locations on the tablet with 3 different illumination angles of 45, 75 and 90°. The spectral variations were more substantial when the tablet faces with engraved letters and greater surface curvature were measured, since the sampled volume of coating relative to that of a core tablet changed significantly under these circumstances as the illumination angle varied. The preliminary examination confirmed that the acquisition of tablet-representative spectra was the requisite for reliable measurement of coating thickness. Then, to mimic real monitoring of coating process, Raman spectra were directly collected on a packing of 30 tablets with repetition of random tablet packing up to 15 times and univariate models utilizing the intensity of coating peak at 638cm-1 were developed using the cumulatively averaged spectra with an average weight of the 30 tablets as a reference. To acquire less tablet orientation-sensitive spectra, a wide area illumination (WAI) scheme providing a large sampling area (28.3mm2) on a tablet with a long focal length (∼25cm) was employed. The averaging of the first to seventh spectra, equivalently utilizing more packing-representative spectra for quantitative analysis, made the measurement of nominal coating thickness of packed tablets accurate.
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