* * * INSIGHT  * * *

Which Shelf Temperature During Lyophilization?

By

Thomas A. Jennings, Ph.D.

ABSTRACT: In the INSIGHT issue Vol. 1 No. 2, it was established that there was, principally during the primary drying process, an interrelationship between the product and shelf temperatures and the chamber pressure. Since the process controlling parameters are the chamber pressure and the shelf temperature, a change in either of theses parameters would lead to a change in the product temperature in the frozen matrix. The principle objective of this INSIGHT was to show how important it was to know the product temperature during the primary drying process. In essence, the product temperature serves to confirm that the shelf temperature and chamber pressure are within their defined limits as established during the validation of the process.

The need for selection of a proper pressure gauge was established in the INSIGHT issue Vol.1 No. 6. This latter issue considered the use of a Pirani gauge in determining the pressure in the chamber. It was shown that the Pirani gauge falls in general classification known as thermoconductivity gauges. These gauges are generally calibrated using dry nitrogen and, as a result of a higher thermal conductivity, the output of the gauge will read false high in the presence of a significant partial pressure of water vapor. These false high pressure readings will occur during most of the primary drying and a portion of the secondary drying when the principle gas component in the drying chamber will be water vapor.

In the case when there is no measure of the product temperature and a thermoconductivity gauge is used to determine the pressure in the chamber,  one must now rely heavily on knowledge of the shelf temperature to control the lyophilization process. But the question that must now be asked is which shelf temperature, i.e., surface or fluid. The following will be a brief discussion of the effect that controlling from shelf-surface or the shelf-fluid will have on a lyophilization process.

Volume 1 Number 7                                                                                   September 1998

2 Pages          0 References           No Figures

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