Additives to biological substances. III. The moisture content and moisture uptake of commonly used carrier agents undergoing processing conditions similar to those used in the preparation of international biological standards.

Aqueous solutions of the carbohydrates alpha alpha'-trehalose, mannitol and lactose, human serum and human albumin were freeze-dried in ampoules and part of each batch was further desiccated over phosphorus pentoxide in a manner similar to that used to prepare international biological standards and related materials. The residual moisture present in the preparations and their uptake of moisture was then measured by Karl Fischer titration. In ampoules open to atmosphere [22 degrees C, 34% relative humidity (RH)] freeze-dried serum, albumin, lactose and alpha alpha'-trehalose all exhibited hygroscopic properties, their moisture contents rising over a period of 24 h, to 10%, 8%, 8% and 7%, respectively. Mannitol when dried to low moisture levels did not exhibit hygroscopic properties, but the residual moisture in different freeze-dried batches was very variable, possibly as a result of that solid's sponge-like and/or crystalline microstructure. When exposed to the same conditions, dried materials in ampoules fitted with polythene capillary leak plugs (used routinely at this Institute during the preparation of Biological Standards) exhibited a considerably reduced rate of moisture uptake. The effect of secondary vacuum drying over phosphorus pentoxide on the moisture content of these preparations is also reported.