Effect of type of container, storage temperature and humidity on the biological activity of freeze-dried alkaline phosphatase.

The suitability of butyl rubber-stoppered vials was compared with that of ampoules for the storage of freeze-dried biological materials under a variety of temperature and humidity conditions using alkaline phosphatase as a model. Immediately after freeze-drying, alkaline phosphatase activity in vials and ampoules was similar but decreased at temperatures of 37 degrees C, 45 degrees C and at cycling temperatures with high relative humidities over the 12-month test period, with the least activity in vials with untreated stoppers. By the end of the study at 12 months post-preparation, moisture levels were lowest (0.4%) in the vials where stoppers had been treated with industrial methylated spirit and air-dried, intermediate (1.0%) in DIN ampoules and highest and most variable (1-4%) in vials with untreated stoppers. There was no apparent exchange between the external atmosphere and that within the vials via the stoppers and the moisture in the vials with untreated stoppers appeared to have originated from the stoppers themselves. It was concluded that the use of vials with treated stoppers was almost as effective as the use of DIN ampoules for the freeze-drying and storage of alkaline phosphatase activity under a range of temperatures and humidities. Fluctuating temperatures were more detrimental to alkaline phosphatase activity than continuous storage at a single high temperature.