Critical factors in the measurement of tablet film coatings using terahertz pulsed imaging

Authors: Daniela Brock, J. Axel Zeitler, Adrian Funke, Klaus Knop, Peter Kleinebudde,
Article first published online: 5 APR 2013; Journal of Pharmaceutical Sciences; DOI: 10.1002/jps.23521
+Wiley Textbooks Periodicals, Inc.

More info at:
http://onlinelibrary.wiley.com/doi/10.1002/jps.23521/abstract

Abstract

The present work gives an insight into some key measurement and signal processing considerations in terahertz pulsed imaging (TPI). TPI is increasingly used for the measurement of the spatial variation of coating thickness on coated solid dosage forms. The potential of TPI for the assessment of coating thickness distributions and the use in process development is described in recent literature. However, some critical factors need to be taken into account when working with this technique. These are (1) the signal processing of the raw data, (2) the influence of the composition of the sample matrix on the TPI signals and subsequent coating analysis, (3) signal distortions that can occur at tablet edges or areas with defects, and (4) the refractive index as a key parameter in the quantification of layer thickness. In this paper, we will highlight to what extent these factors impact on the qualitative and quantitative analysis of TPI data and how artifacts and misinterpretation of data can be avoided to ensure fully quantitative and robust measurements.

More about terahertz pulsed imaging for the study of Pharmaceutical tablets:
http://www.teraview.com/applications/pharmaceutical/terahertz-pulsed-imaging.html

Terahertz pulsed imaging as an advanced characterisation tool for film coatings—A review

International Journal of Pharmaceutics
Available online 6 April 2013
http://dx.doi.org/10.1016/j.ijpharm.2013.03.053

Authors: Miriam Haaser^{a, b, c}, Keith C. Gordon^d, Clare J. Strachan^e, Thomas Rades^f
a School of Pharmacy, +University of Otago, P.O. Box 56, Dunedin, New Zealand
b Cavendish Laboratory, +Cambridge University Press Education , Cambridge CB3 0HE, UK
c +TeraView Ltd., St. John's Innovation Park, Cambridge CB4 0WS, UK
d Department of Chemistry, MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago, Dunedin, New Zealand
e Division of Pharmaceutical Technology, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland
f Department of Pharmacy, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark

Abstract

Solid dosage forms are the pharmaceutical drug delivery systems of choice for oral drug delivery. These solid dosage forms are often coated to modify the physico-chemical properties of the active pharmaceutical ingredients (APIs), in particular to alter release kinetics. Since the product performance of coated dosage forms is a function of their critical coating attributes, including coating thickness, uniformity, and density, more advanced quality control techniques than weight gain are required. A recently introduced non-destructive method to quantitatively characterise coating quality is terahertz pulsed imaging (TPI). The ability of terahertz radiation to penetrate many pharmaceutical materials enables structural features of coated solid dosage forms to be probed at depth, which is not readily achievable with other established imaging techniques, e.g. near-infrared (NIR) and Raman spectroscopy. In this review TPI is introduced and various applications of the technique in pharmaceutical coating analysis are discussed. These include evaluation of coating thickness, uniformity, surface morphology, density, defects and buried structures as well as correlation between TPI measurements and drug release performance, coating process monitoring and scale up. Furthermore, challenges and limitations of the technique are discussed.


... The imaging unit in TPI instruments such as the TPI imaga 2000 system (TeraView, Cambridge, UK), therefore comprises a six-axis robotic arm, the probe and a separate optical laser operating at 670 nm. ...

More info at :http://www.sciencedirect.com/science/article/pii/S0378517313002834