Thursday, 23 May 2013

Non-destructive measurement of polymer coatings on pharmaceutical tablets using X-ray micro CT and terahertz pulsed imaging

Authors: Isabelle-Sophie Russe1,2, Daniela Brock1,2, Klaus Knop2, Peter Kleinebudde2, J. Axel Zeitler1=
1 Department of Chemical Engineering and Biotechnology, University of Cambridge,  Cambridge, UK
Institute of Pharmaceutics and Biopharmaceutics, University of Duesseldorf, Duesseldorf, Germany

Full text:


We conclude that TPI is a robust technique, and, that due to its very simple measurement  principle, it is an ideal measurement technique to quantify the coating thickness in process control and quality monitoring applications. The method introduced in this paper will be useful to explore whether there is an influence on  the refractive index of a given coating formulation with changes in process conditions during  coating or curing. It furthermore opens the possibility, in pharmaceutical applications and  beyond, to develop metrology standards for coatings that can be used to calibrate TPI  measurements for absolute thickness.
Beyond its use as a calibration technique for TPI the XµCT method has provided some  intriguing insight into the coating properties at extremes of the tablet geometry, at the edges  of tablets where high curvature was thought to typically prevent quantitative TPI  measurements due to strong scattering. The main limitations of the XµCT technique are the  measurement, and in particular, processing time together with the high demands in  computational power and data storage as well as the limited contrast that can be resolved  between coating and core. We therefore envisage that the main impact of this technique is likely to be in research and development and to support techniques such as TPI rather than  in routine quality control or process measurements.

...Samples were measured on a TPI imaga 2000 (Teraview Ltd., Cambridge, UK), using a point spacing grid of 200 x 200 µm and a penetration depth of 1 mm in air...