Effect of crystal size and shape on bulk density of pharmaceutical powders

Bulk density is one of the important pharmaceutical characteristics of pharmaceutical powders. Though not required by Pharmacopoeias, it is often declared in the certificate of analysis of different pharmaceutical raw materials. It directly influences the preparation of different pharmaceutical forms: suspensions, capsules, tablets, etc. The effect of the size and shape of crystals on the bulk density of pharmaceutical powders was studied. As the model substance, 5-aminosalicylic acid was used. The crystals of 5-aminosalicylic acid were obtained by precipitation of the crude product dissolved in a dilute acid, by a dilute base to the equivalence point. The different parameters influence the crystals size and shape. According to the precipitation conditions, two types of product were obtained: regular bulk density (loose) 0.10-0.35 g/ml (N-type) and high bulk density 0.35-0.60 g/ml (C-type).