Understanding dissolution phenomena of spray dried powders using a single particle approach

Abstract

History studies of particle dissolution have been focused on both “bulk approach” and “single approach”. The link between these two approaches can reveal inter-particle cohesive effect but it is rarely reported. The presented work addresses this scientific challenge by investigating individual particle dissolution kinetics, using Monte Carlo analysis to convert results to bulk particle dissolution profiles, and comparing them to experimental results of bulk particle dissolution kinetics. The impact of binder materials on inter-particle cohesive effect has been studied using spray-dried powders with a binary matrix formulation. Dissolution of individual particles across size range was observed under an optical microscope and analysed by Image Processing. The results were used to predict bulk particles dissolution profiles via a Monte Carlo analysis. Meanwhile, chemical measurement (conductivity) of bulk particle dissolution was carried out for the same sample. The comparison between Monte Carlo analysis and chemical measurements showed a good agreement for the samples without binder and with mix binder (Citric Acid + MgSO4 + Zeolite). For the samples with Silicate as binder material, the comparison did not correlate well, chemical measurement shows a generally faster dissolution for bulk particles than Monte Carlo analysis, and higher Silicate concentration in particles results in larger difference. This is mainly due to the polymerization of Silicate that forms a “shell” structure around the particle and slows down dissolution for individual particles. However, in bulk particle dissolution, high salt concentration in the local area around particles breaks polymerization of Silicate and reduces the effect on particle dissolution. Consequently, it is proposed that Monte Carlo analysis of individual particle dissolution can be used to compare to bulk particle dissolution in order to reveal inter-particle cohesive effect on particle dissolution kinetics.