Freeze drying and residual moisture

Abstract

Several factors associated with operation of freeze-drying equipment and residual moisture determinations have been discussed in relation to their influence on the residual moisture content of the product or on the determination of the residual moisture. Factors which should be achieved in the freeze-drying process are a relatively open physical structure of the mass as it is being dried, the presence of additives which improve the physical structure of the mass or provide protection to otherwise labile components, good heat transfer from the shelves to the product, and removal of moisture from rubber stoppers. Important factors which can influence the results from residual moisture determinations are the sample size which preferably should be at least 200 mg, transfer of samples which should be in a low-humidity atmosphere, isolation of samples by handling only one at a time in a low-humidity box and by use of separate desiccators, and monitoring the procedure with highly hygroscopic material as a test of its ability to yield valid results.