Terahertz-based porosity measurement of pharmaceutical tablets: a tutorial

Prince Bawuah, Daniel Markl, Daniel Farrell, Mike Evans, Alessia Portieri, Andrew Anderson, Ralph Lucas, J. Axel Zeitler

Research output: Contribution to journalArticle

Abstract

Porosity, one of the important quality attributes of pharmaceutical tablets, directly affects the mechanical properties, the mass transport and hence tablet disintegration, dissolution and ultimately the bioavailability of an orally administered drug. The ability to accurately and quickly monitor the porosity of tablets during manufacture or during the manufacturing process will enable a greater assurance of product quality. This tutorial systematically outlines the steps involved in the terahertz-based measurement method that can be used to quantify the porosity of a tablet within seconds in a non-destructive and non-invasive manner. The terahertz-based porosity measurement can be performed using one of the three main methods, which are (i) the zero-porosity approximation (ZPA); (ii) the traditional Bruggeman effective medium approximation (TB-EMA); and (iii) the anisotropic Bruggeman effective medium approximation (AB-EMA). By using a set of batches of flat-faced and biconvex tablets as a case study, the three main methods are compared and contrasted. Overall, frequency-domain signal processing coupled with the AB-EMA method was found to be most suitable approach in terms of accuracy and robustness when predicting the porosity of tablets over a range of complexities and geometries. This tutorial aims to concisely outline all the necessary steps, precautions and unique advantages associated with the terahertz-based porosity measurement method.
Original languageEnglish
Pages (from-to)450-469
Number of pages20
JournalJournal of Infrared, Millimeter and Terahertz Waves
Volume41
Issue number4
Early online date11 Jan 2020
DOIs
Publication statusPublished - 30 Apr 2020

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Keywords

  • terahertz spectroscopy
  • pharmaceutical tablet
  • porosity
  • effective medium approximation
  • refractive index
  • optical path length

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