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Transmission Raman spectroscopy is a potent new tool for content uniformity testing in pharmaceutical manufacturing enabling rapid bulk sampling of a material by non-destructive means. In this proof-of-concept study, we present, for the first time, comprehensive quantification of all the constituents in a set of tablets consisting of 5 components (3 APIs and 2 excipients) by this method. The nominal concentration of individual components ranged from 1 to 85% (w/w). Two multivariate partial least-squares approaches have been used to calibrate concentration models consisting of 40 handmade tablets covering 20 sample points. These models successfully predicted all the components in a set of 10 validation tablets covering 5 different sample points. A single model for all components (PLS2) and 5 individual models each optimised for one component (PLS1) performed similarity and have been used to demonstrate that specificity of prediction has been achieved through using a multifactor orthogonal DoE for sample preparation. The ability to determine multiple analyte concentrations in one single measurement further establishes this procedure and its benefits for assay and content uniformity testing.

Original publication





Journal of pharmaceutical and biomedical analysis

Publication Date





277 - 282


Cobalt Light Systems Ltd, 174 Brook Drive, Milton Park, Abingdon, Oxfordshire, OX14 4SD, UK.


Phenylephrine, Acetaminophen, Caffeine, Tablets, Excipients, Calibration, Spectrum Analysis, Raman, Multivariate Analysis, Least-Squares Analysis, Reproducibility of Results, Models, Theoretical