Determination of Water Content of Crystalline Pharmaceutical Solids under Different Percentages of Relative Humidity

It is reported that the change in the number of water molecules in the crystalline mineral salts which is used as pharmaceutical ingredients, can cause variations in their physicochemical and pharmaceutical properties. The number of water molecules of these pharmaceutical ingredients is subordinate to Relative Humidity (RH) and temperature of the maintenance environments of the medicines. The aim of the present study was to investigate variation in water content of pharmaceutical solids including ferrous sulfate, barium sulfate and magnesium chloride in different percentage of RH and temperature. For this purpose, the pharmaceutical solids (both inside and outside the packaging) were subjected to various relative humidity at constant temperature for a given period of time, then change in their water content was determined with Thermo Gravimetry Analysis (TGA). To create a variety environments with different RH in constant temperature, the saturated salt solutions were put in a desiccator and the RH above mixtures of solids was determined with a Hygroscope at 25°C. According to the results obtained from TGA, the water content of pharmaceutical solids studied in this research (ferrous sulfate, barium sulfate and magnesium chloride) changed in different RH and temperatures. It is necessary to determine water uptake of Active Pharmaceutical Ingredients (APIs) and excipients in each stage of pharmaceutical development process. Furthermore, these results could be used to select an appropriate packaging to avoid adverse effects caused by water absorption by pharmaceutical solids. In cases where this is not possible, the allowable range of relative humidity for each pharmaceutical solid should be noted on its package.