Development of a Remote Electrode System for Monitoring the Water Content of Materials Inside a Glass Vial

Purpose: This article explores the use of a remote electrode dielectric measurement system to monitor the water content of hydrated ovalbumin inside a glass vial. Methods: The intrinsic dielectric properties of hydrated ovalbumin were characterized first using conventional parallel plate electrodes. The second stage was to simulate a remote electrode measurement by placing nonconductive, nondispersive polyethylene films between the sample and electrodes. Finally, a study on the dielectric measurement of ovalbumin contained in a 10 ml glass vial was undertaken with the electrodes external to the glass vial. Results: The dielectric behavior of hydrated ovalbumin was characterized by charge transfer (i.e., protons) in the hydrogen bonded network of water molecules in the bulk sample. The mechanism was identified as an anomalous low-frequency dispersion and a dielectric loss peak (₃). The dielectric relaxation time, ₃, of the ₃ dispersion was especially sensitive to water content. Moreover, a good correlation (R² = 93%) was observed between relaxation times ₃ obtained from measurements using conventional parallel plate electrodes and the remote electrode system. Conclusions: Dielectric measurements using remote electrodes attached to a glass vial are therefore applicable for the in situ measurement of water content in materials. The application of this technology to the determination of the lyophilization end point is suggested.