title: Detection of porosity of pharmaceutical compacts by terahertz radiation transmission and light reflection measurement techniques.
abstract: 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.
authors: Institute of Photonics, University of Eastern Finland, P. O. Box 111, FI-80101 Joensuu, Finland. Electronic address: prince.bawuah@uef.fi.
authors: Prince
authors: P
authors: Bawuah
authors: Institute of Photonics, University of Eastern Finland, P. O. Box 111, FI-80101 Joensuu, Finland.
authors: Alessandra
authors: A
authors: Pierotic Mendia
authors: Institute of Photonics, University of Eastern Finland, P. O. Box 111, FI-80101 Joensuu, Finland.
authors: Pertti
authors: P
authors: Silfsten
authors: Institute of Photonics, University of Eastern Finland, P. O. Box 111, FI-80101 Joensuu, Finland.
authors: Pertti
authors: P
authors: Pääkkönen
authors: School of Pharmacy, Promis Centre, University of Eastern Finland, P. O. Box 1617, FI-70211, Joensuu, Finland.
authors: Tuomas
authors: T
authors: Ervasti
authors: School of Pharmacy, Promis Centre, University of Eastern Finland, P. O. Box 1617, FI-70211, Joensuu, Finland.
authors: Jarkko
authors: J
authors: Ketolainen
authors: Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB2 3RA, United Kingdom.
authors: J Axel
authors: JA
authors: Zeitler
authors: Institute of Photonics, University of Eastern Finland, P. O. Box 111, FI-80101 Joensuu, Finland.
authors: Kai-Erik
authors: KE
authors: Peiponen
mesh_terms: D002482:Cellulose / Q000737:chemistry*; D016062:Porosity; D013499:Surface Properties; D013607:Tablets; D013678:Technology, Pharmaceutical / Q000379:methods*; D055053:Terahertz Radiation; D055068:Terahertz Spectroscopy
chemical_list: D013607:Tablets; D002482:Cellulose; C109691:microcrystalline cellulose
keywords: Intrinsic refractive index; Pharmaceutical tablets; Porosity; Specular gloss; Surface roughness; Terahertz