Analysis of moisture sorption hysteresis in hard gelatin capsules, maize starch, and maize starch: drug powder mixtures

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Abstract
Moisture sorption and desorption isotherms at 25°C for hard gelatin capsules, maize starch and 50:50 mixes of maize starch: barbitone and maize starch: sodium barbitone have been measured. The sorption hysteresis observed in all four systems studied has been analysed according to the hypothesis of Young & Nelson (1967a) which distinguishes three locations for moisture—monolayer adsorbed moisture, normally condensed moisture and absorbed moisture. Hysteresis is explained by a separation of absorption and desorption isotherms for absorbed moisture and different patterns of moisture distribution are demonstrated in the four systems examined.