Detection of porosity of pharmaceutical compacts by terahertz radiation transmission and light reflection measurement techniques
Abstract
We report on the non-destructive quantification of the porosity of pharmaceutical compacts (microcrystalline cellulose tablets) by using both optical and terahertz techniques. For the full analysis of the porosity of pharmaceutical tablets, the results obtained in both cases have shown that optical and terahertz techniques are complementary. The intrinsic refractive index of microcrystalline cellulose was estimated using the effective refractive index obtained from the time delay of the THz pulse together with the Bruggeman model for effective media. Once this intrinsic refractive index is known, the unknown porosity of the tablet can be estimated with the aid of the measured effective refractive index as well as the thickness of the pharmaceutical tablet. The method was tested using a set of thirteen tablets having different porosities. It is shown that the error in the estimation of the unknown tablet's porosity is less than 1%. In addition, surface roughness was measured by using an optical interferometer and gloss by using a diffractive-optical-element based glossmeter. The measurement was achieved by scanning the tablets with a probe beam and detecting the reflected light. The surface roughness and gloss data show relatively good correlation with the porosities of the tablets.
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THz-TDS in conjunction with the Bruggeman effective medium approximation can be used to nondestructively and non-invasively measure the porosity of pharmaceutical tablets.
“Around the mid 2010s, Bawuah et al. [40] successfully demonstrated that THz-TDS in conjunction with the Bruggeman effective medium approximation can be used to nondestructively and non-invasively measure the porosity of pharmaceutical tablets.”
From Terahertz-Based Porosity Measurement of Pharmaceutical Tablets: a Tutorial (2020) · cites this paper as [40]
The Bruggeman model could be used to accurately measure the porosity of flat-faced compacts containing only microcrystalline cellulose (MCC) and air, despite its basic assumption that the inclusions are of spherical shape.
“Despite its basic assumption that the inclusions are of spherical shape, the Bruggeman model could be used to accurately measure the porosity of flat-faced compacts containing only microcrystalline cellulose (MCC) and air [40].”
From Terahertz-Based Porosity Measurement of Pharmaceutical Tablets: a Tutorial (2020) · cites this paper as [40]
The Bruggeman model is valid for tablets with a wide range of porosity.
“In that preliminary study, the authors adopted the Bruggeman model due to its validity for tablets with a wide range of porosity.”
From Terahertz-Based Porosity Measurement of Pharmaceutical Tablets: a Tutorial (2020) · cites this paper as [40]
Total porosity can be calculated from a THz-TDS measurement by using effective medium theory and knowing the intrinsic refractive index of the solid matrix.
“The total porosity can thus be calculated from a THz-TDS measurement by utilizing effective medium theory and knowing the intrinsic refractive index of the solid matrix.”
From Measuring Open Porosity of Porous Materials Using THz-TDS and an Index-Matching Medium (2020) · cites this paper as [21]
THz-TDS has been demonstrated to measure porosity of rocks and pharmaceutical tablets and to analyze anisotropy of pore structures.
“This method has been demonstrated to measure the porosity of rocks [20] and pharmaceutical tablets [21,22,23] as well as to analyze the anisotropy of pore structures [18,24].”
From Measuring Open Porosity of Porous Materials Using THz-TDS and an Index-Matching Medium (2020) · cites this paper as [21]
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- Authors
- Bawuah, P., Pierotic Mendia, A., Silfsten, P., Pääkkönen, P., Ervasti, T., Ketolainen, J., Zeitler, J. A., & Peiponen, K.-E.
- Affiliations
- University of Eastern Finland (FI)
- University of Cambridge (GB)
- Corresponding author
- Bawuah, Prince
- Venue
- International Journal of Pharmaceutics
- Publisher
- Elsevier BV
- Published
- 2014-04
- Volume
- 465
- Issue
- 1-2
- Pages
- 70-76
- ISSN
- 0378-5173 (ISSN-L)
- OpenAlex
- W2016076718
- Cited by
- 70
- References
- 32
- Citations by year
- 2026: 2 · 2025: 7 · 2024: 3 · 2023: 4 · 2022: 2 · 2021: 6 · 2020: 11 · 2019: 4 · 2018: 5 · 2017: 10 · 2016: 9 · 2015: 6 · 2014: 1
- FWCI
- 4.61
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- International Journal of Pharmaceutics (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Physical Sciences › Engineering › Electrical and Electronic Engineering › Terahertz technology and applications
- Health Sciences › Medicine › Public Health, Environmental and Occupational Health › Pharmaceutical Quality and Counterfeiting
- Physical Sciences › Chemistry › Analytical Chemistry › Analytical Methods in Pharmaceuticals
- Keywords
- tablet porosity, microcrystalline cellulose, refractive index, surface roughness, glosses
- MeSH terms
- Cellulose, Surface Properties, Tablets, Technology, Pharmaceutical, Porosity, Terahertz Radiation, Terahertz Spectroscopy
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