Electrical Impedance Methods for Developing a Lyophilization Cycle. Podium presentation at ISL-FD 9th International Conference 2-6th September, 2019, Ghent, Belgium
The talk will describe the application of through-vial impedance spectroscopy in the determination of in-vial phase behaviour during freezing and annealing.
• Through-Vial Impedance Spectroscopy – An Introduction
• Dielectric loss mechanisms in frozen solutions
• Measurement frequency selection for different facets of the freezing process (ice nucleation to solidification end point)
• Determination of in-vial glass transitions
TVIS dielectric storage parameter C' at low frequency (e.g. 10 or 100 Hz) allows for the registration of ice nucleation (ice growth onset) partly due to its dependence on temperature whereas C' at high frequency (e.g. 200 kHz) shows less sensitivity to temperature and so is an ideal measurement frequency for assessing the end point of ice solidification.
Post solidification, the TVIS parameter log Fpeak is used determine the point at which all excess latent heat has left the sample and the product temperature then equilibrates with the shelf.
This work paves the way for the non-invasive determination of the ice nucleation temperature, the average ice growth rate and the time interval between ice solidification end point and thermal equilibration.