Abstract-Detection of porosity of pharmaceutical compacts by terahertz radiation transmission and light reflection measurement techniques.

Bawuah P1, Mendia AP2, Silfsten P2, Pääkkönen P2, Ervasti T3, Ketolainen J3, Zeitler JA4, Peiponen KE2.

Author Information

• 1Institute of Photonics, University of Eastern Finland, P. O. Box 111, FI-80101 Joensuu, Finland. Electronic address: prince.bawuah@uef.fi.
• 2Institute of Photonics, University of Eastern Finland, P. O. Box 111, FI-80101 Joensuu, Finland.
• 3School of Pharmacy, Promis Centre, University of Eastern Finland, P. O. Box 1617, FI-70211, Joensuu, Finland.
• 4Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB2 3RA, United Kingdom.

http://www.ncbi.nlm.nih.gov/pubmed/24530384

We report on the non-destructive quantification of the porosity of pharmaceutical compacts (microcrystalline cellulose tablets) by using both optical and terahertz techniques. For the full analysis of the porosity of pharmaceutical tablets, the results obtained in both cases have shown that optical and terahertz techniques are complementary. The intrinsic refractive index of microcrystalline cellulose was estimated using the effective refractive index obtained from the time delay of the THz pulse together with the Bruggeman model for effective media. Once this intrinsic refractive index is known, the unknown porosity of the tablet can be estimated with the aid of the measured effective refractive index as well as the thickness of the pharmaceutical tablet. The method was tested using a set of thirteen tablets having different porosities. It is shown that the error in the estimation of the unknown tablet's porosity is less than 1%. In addition, surface roughness was measured by using an optical interferometer and gloss by using a diffractive-optical-element based glossmeter. The measurement was achieved by scanning the tablets with a probe beam and detecting the reflected light. The surface roughness and gloss data show relatively good correlation with the porosities of the tablets.

Copyright © 2014. Published by Elsevier B.V.