Investigating the moisture-induced crystallization kinetics of spray-dried lactose.

Gravimetric water sorption experiments were performed to study the crystallization behavior of amorphous spray-dried lactose over a wide range of temperature and humidity conditions. Experiments performed at 25 degrees C between 48 and 60% relative humidity (RH) showed that the onset time to crystallization increased dramatically with decreasing humidity. At 55% RH and above, crystallization occurred in a single detectable step, while below a two-step process was observed.

Quantitative characterization of adsorption isotherms using isothermal microcalorimetry.

The integral heat of adsorption of water vapor on sodium benzoate samples was determined at various partial vapor pressures using a heat conduction microcalorimeter. An equation is presented to describe the calorimetric integral heat response (mJ/g of solid) as a function of relative humidity. This equation, although similar in principle to the well-known BET equation, relates the heat evolved (rather than volume or mass of gas adsorbed) upon adsorption to the partial pressure of the gas.

Calorimetric determination of the heat of precipitation of pseudoephedrine racemic compound--its agreement with the heat of solution.

The heat of precipitation of dl-pseudoephedrine was determined by direct calorimetry using a Tronac isoperibolic calorimeter. The precipitation of dl-pseudoephedrine was induced by mixing aqueous solutions of the two enantiomers, namely, d- and l-pseudoephedrine, directly in the calorimeter. The molar heat of precipitation of dl-pseudoephedrine was -2.

Dielectric analysis in the characterization of amorphous pharmaceutical solids. 1. Molecular mobility in poly(vinylpyrrolidone)-water systems in the glassy state.

The effect of water on the relaxation behavior below the glass transition temperature (beta-relaxation) of an amorphous powder, poly(vinylpyrrolidone) (PVP, MW 30,000), was studied by subjecting the sample to dielectric analysis in the frequency range from 20 Hz to 20 kHz. The material stored at 0% relative humidity (RH) (containing 0.05% w/w H2O) exhibited a frequency dependent second-order beta-relaxation (T beta = -56 degrees C at 500 Hz).

Studies on the in-vitro percutaneous penetration of indomethacin from gel systems in hairless mice.

The influence of co-solvents on the in-vitro percutaneous penetration of indomethacin from gel systems was studied using a simplex lattice experimental design. Gel formulations were prepared by gelling the vehicle mixture of water, either alcohol or isopropanol and either propylene glycol or PEG 400 with 1% w/w Carbomer 940. Hairless mouse skin was employed as the barrier in a Franz-type diffusion cell.