Evaluation of risk and benefit in the application of near-infrared spectroscopy to monitor the granule coating process.

The purpose of this article is to study risk and benefit in the application of near-infrared (NIR) spectroscopy to the coating process of granules to monitor the process for determining the coating end point. Cylindrical granules or spherical granules were used as core granules and were coated using a fluidized bed coating apparatus by spraying coating suspension. During the coating run, samples of granules were pulled at regular intervals and amount of talc or lactose, which were the components of the film layer, were estimated by NIR spectroscopy. When the coating layer of granules was thin like the case of the spherical granules, it was possible to monitor and understand the coating process well by an application of NIR spectroscopy, because it was possible to estimate some components in the coating layer simultaneously. However, it was found that as the coating layer became thick like the case of the cylindrical granules, NIR light was scattered by titanium dioxide in the coating layer, and that the increase of the coating layer estimated from NIR spectroscopy showed the misunderstanding saturation. NIR spectroscopy could not be used for the estimation of the granule coating process even if the formulation and amount applied for the coating was same as the spherical granules. When NIR spectroscopy is intended to be used to control granule coating process, it is necessary to check the impacts of the formulation applied for coating, the amount of the coating layer, and the thickness of the coating layer on the estimations.