Water-induced charge transport in tablets of microcrystalline cellulose of varying density: Dielectric spectroscopy and transient current measurements
2003 (English)In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 295, no 2, 159-165 p.Article in journal (Refereed) Published
Room temperature dielectric frequency response data taken over 13 decades in frequency on microcrystalline cellulose (MCC) tablets of varying density are presented. The frequency response shows on three different processes: the first one is a high-frequency relaxation process whose magnitude increases and reaches a plateau as the tablet density increases. This process is associated with orientational motions of local chain segments via glycosidic bonds. The second relaxation process, related to the presence of water in the MCC matrix, is insensitive to changes in tablet density. At lower frequencies, dc-like imperfect charge transport dominates the dielectric spectrum. The dc conductivity was found to decrease with increasing tablet density and increase exponentially with increasing humidity.
Transient current measurements indicated that two different ionic species, protons and OH− ions, lied behind the observed conductivity. At ambient humidity of 22%, only one in a billion of the water molecules present in the tablet matrix participated in long range dc conduction. The diffusion coefficient of the protons and OH− ions were found to be of the order of 10−9 cm2/s, which is the same as for small salt building ions in MCC. This shows that ionic drugs leaving a tablet matrix may diffuse in the same manner as the constituent ions of water and, thus, elucidates the necessity to understand the water transport properties of excipient materials to be able to tailor the drug release process from pharmaceutical tablets.
Place, publisher, year, edition, pages
2003. Vol. 295, no 2, 159-165 p.
Microcrystalline cellulose; Tablets; Dielectric spectroscopy; Transient currents; Water; Protons; Diffusion
IdentifiersURN: urn:nbn:se:uu:diva-94363DOI: 10.1016/j.chemphys.2003.09.001OAI: oai:DiVA.org:uu-94363DiVA: diva2:168189