Sputtered thermocouple array for vial temperature mapping

Abstract

This paper describes the development and characterization of a thin film thermocouple array to be used as a non-invasive solution to map the temperature distribution inside small vials used for freeze-drying pharmaceutical chemicals. Pharmaceutical chemicals are often produced by means of freeze-dryers with very good results, even though the slowness of drying process may increase the product cost. Increasing the shelf temperature accelerates the drying process, but can increase the risk of melting and damaging the product. This risk could be minimized by following the product temperature evolution during the drying step, by means of a noninvasive measuring system able to perform an in situ continuous monitoring. Actual sensors are too invasive to permit a reliable measurement and in addition their dimension does not allow to employ many sensors in a small volume. This paper describes the development of a new multi-sensor structure based on an array of thermocouples having nanometric thickness. The thermocouple array can be embedded into the glass wall of a test vial having all the other characteristics equal to the remaining batch thus providing meaningful and reliable results. Prototypes of the proposed thermocouple array have already been realized and tested making it possible to map the temperature at intervals of few millimeters, following the ice edge during lyophilization.