Problems with freeze drying plants

Insensitive to impact, it decomposes, sometimes explosively, above its m.p. [1], particularly if heated rapidly [2], Although used in aqueous solutions as a preservative in pharmaceutical preparations, application of freeze-drying techniques to such solutions has led to problems arising from volatilisation of traces of hydrazoic acid from non-neutral solutions, condensation in metal lines, traps or filters, and formation of heavy metal azides in contact with lead, copper or zinc components in the drying plant [3,4],... 

Although the drying process progresses on the basis of the preprogrammed profile of shelf temperature and chamber pressure with time, there can be variation in terms of temperature within a shelf and across the chamber itself. The mapping of the variation in temperature across the freeze-dryer is an important part of the qualification of a new plant and should be repeated periodically, especially if problems are suspected in coolant flow path etc. 

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