title: Design, development and method validation of a novel multi-resonance microwave sensor for moisture measurement.
abstract: Microwave sensor systems using resonance technology at a single resonance in the range of 2-3 GHz have been shown to be a rapid and reliable tool for moisture determination in solid materials including pharmaceutical granules. So far, their application is limited to lower moisture ranges or limitations above certain moisture contents had to be accepted. Aim of the present study was to develop a novel multi-resonance sensor system in order to expand the measurement range. Therefore, a novel sensor using additional resonances over a wide frequency band was designed and used to investigate inherent limitations of first generation sensor systems and material-related limits. Using granule samples with different moisture contents, an experimental protocol for calibration and validation of the method was established. Pursuant to this protocol, a multiple linear regression (MLR) prediction model built by correlating microwave moisture values to the moisture determined by Karl Fischer titration was chosen and rated using conventional criteria such as coefficient of determination (R2) and root mean square error of calibration (RMSEC). Using different operators, different analysis dates and different ambient conditions the method was fully validated following the guidance of ICH Q2(R1). The study clearly showed explanations for measurement uncertainties of first generation sensor systems which confirmed the approach to overcome these by using additional resonances. The established prediction model could be validated in the range of 7.6-19.6%, demonstrating its fit for its future purpose, the moisture content determination during wet granulations.
authors.affiliation: Heinrich-Heine-University Düsseldorf, Institute of Pharmaceutics and Biopharmaceutics, Düsseldorf, Germany; NextPharma Waltrop, Pharbil Waltrop GmbH, Waltrop, Germany. Electronic address: johanna.peters@hhu.de.
authors.forename: Johanna
authors.initials: J
authors.lastname: Peters
authors.affiliation: Christian-Albrechts-University Kiel, Institute of Electrical Engineering and Information Technology, Kiel, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Taute
authors.affiliation: NextPharma Waltrop, Pharbil Waltrop GmbH, Waltrop, Germany.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Bartscher
authors.affiliation: Döscher Microwave Systems GmbH, Hamburg, Germany.
authors.forename: Claas
authors.initials: C
authors.lastname: Döscher
authors.affiliation: Christian-Albrechts-University Kiel, Institute of Electrical Engineering and Information Technology, Kiel, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Höft
authors.affiliation: Christian-Albrechts-University Kiel, Institute of Electrical Engineering and Information Technology, Kiel, Germany.
authors.forename: Reinhard
authors.initials: R
authors.lastname: Knöchel
authors.affiliation: Heinrich-Heine-University Düsseldorf, Institute of Pharmaceutics and Biopharmaceutics, Düsseldorf, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Breitkreutz
keywords: Granule moisture; ICH Q2 method validation; Microwave resonance technology; Moisture measurement; Multiple linear regression; Process analytical technology (PAT)