A centrifuge technique for the evaluation of the extent of water movement in wet powder masses

A centrifuge method has been applied to the assessment of water retention i n pharmaceutical powders. Five drug models and microcrystalline cellulose ( MCC) were each mixed with different amounts of water and centrifuged at dif ferent speeds. The amount of water retained by the wet mass was evaluated b y drying the powders to constant weight. Binary mixtures of each of the fiv e model drugs, MCC and water were also processed in the same way. From the amount of water extracted the moisture retention capacity (MRC) was calcula ted. The MCC retained water more strongly than the different drug models ov er a wider range of initial water contents. The five drug models, although similar in their chemical structure, were divided into two groups, in terms of their MRC values. 4-HBA and propyl gallate recorded higher MRC values t han methyl, propyl and butyl paraben. For the drug models mixed with MCC, t he MRC values recorded were similar, though it was still possible to divide the drugs into the two subgroups. A correlation between the MRC value reco rded for the different systems and the hydrogen bonding solubility componen t was found. The application of different centrifuge speeds indicated that within the same material there were different mechanisms of water retention . (C) 1999 Published by Elsevier Science B.V. All rights reserved.