An Introduction to Through‐Vial Impedance Spectroscopy (TVIS)

Résumé fourni par la source

This chapter describes the instrumentation and operating principles of through-vial impedance spectroscopy (TVIS) for monitoring pharmaceutical freeze-drying. It begins with the design of the TVIS vial and the determination of fill height and volume, followed by noninvasive temperature calibration using nearest-neighbor thermocouple-containing vials. The construction and function of the cabling, junction box, feedthrough plate, and vacuum-flange adapters are then detailed, explaining how the measurement system integrates within different freeze dryers. The chapter outlines the measurement sequence and data capture using the LyoView® software, before introducing the electrical model of the TVIS vial and the role of equivalent-circuit representations. Applications to freeze-drying are presented in terms of the dielectric relaxation of ice, the Maxwell–Wagner effect, and glass-wall artefacts. The chapter then concludes with the development history of the TVIS system with an annex providing some fundamentals of impedance spectroscopy.

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