Comparative study of non-destructive methods to quantify thickness of tablet coatings.

The Supercell coater is a newly introduced coater which utilizes air fluidization for tablet coating. The aim of this study was to define a suitable, fast and non-destructive method for the quantification of coat thickness for Supercell-coated tablets. Various coat thickness characterization methods were carried out on tablets coated at different process conditions. These include the use of optical microscopy, micrometer, X-ray fluorescence (XRF), Raman and near-infrared (NIR) spectroscopy. Coat thicknesses obtained from direct measurements were used to calibrate the spectral data from spectroscopic methods for model generation. The models were subsequently validated to evaluate their prediction capabilities, especially the ability to differentiate tablets coated at different conditions. XRF spectroscopy was viewed to be more suitable for the assessment of process yield and efficiency but both Raman and NIR spectroscopy were shown to be more appropriate methods for the rapid prediction and evaluation of coat thickness. However, only Raman spectroscopy was able to differentiate tablets coated under different conditions accurately. In conclusion, direct thickness measurements were more time-consuming but provided assured coat thickness data. On the other hand, XRF, Raman and NIR spectroscopy methods were viable alternatives to provide complementary information for the study of tablet coatings.