Methods for determining favorable conditions for freeze-drying biological reference materials

By predetermining favorable conditions for freeze-drying samples through pilot runs, one can gain more assurance that relatively large batches of lyophilized biological reference materials produced have the desired characteristics. Included in the pilot studies are the determination of the characteristics of the lyophilizer with a specific freeze-drying cycle, simulation of the water load expected for the production run, residual moisture analyses of the lyophilized samples, and biological activity of the samples before lyophilization and after exposure to elevated temperatures. Various reference materials have been lyophilized by these procedures. Among them are clinical chemistry reference samples, bacterial suspensions, and candidate serum-protein reference immunological standards. A batch of 6,300 vials of the latter was successfully freeze-dried and showed less than 0.1% residual moisture; different proteins (including complement) were both functionally (enzymatically) and antigenically active.