Confocal raman microscopy as a tool to investigate concentration profiles of melt crystallized ibuprofen/carnauba wax

Haiyan Qu, Eric Römbach, Marjatta Louhi-Kultanen, Matthew J. Jones, Joachim Ulrich*

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

4 Citations (Scopus)


Coatings are of great significance for pharmaceutical solid dosage forms. They fulfil a number of functions and are often necessary to control drug delivery, to mask bitter taste, or to protect the active pharmaceutical ingredient from detrimental environmental factors. The process of self-coating by melt crystallization of a suitable binary mixture eliminates the need for an additional process step in the manufacture of a solid drug. Self-coating relies upon the physical and spatial separation of individual components in a melt during solidification. This paper focuses on the use of confocal Raman microscopy as a nondestructive technique for quantifying the spatial distribution of the components in self-coated pastilles manufactured from the binary system ibuprofen/carnauba wax. Pastilles are produced from the melt. Raman spectroscopy allows the direct analysis of concentration profiles across the surface of the pastille. Here, the samples are cleaved and the cleaved surface is investigated in order to establish the distribution of the components in the interior of the solid. A univariate calibration model was developed and statistically validated with standard mixtures of ibuprofen and carnauba wax. Different regression models (linear or polynomial, using different significant peaks for the respective compounds) were assessed and a linear model was found to be adequate to determine the concentration gradient in the pastilles.

Original languageEnglish
Pages (from-to)1113-1119
Number of pages7
JournalChemical Engineering and Technology
Issue number7
Publication statusPublished - Jul 2009
MoE publication typeA1 Journal article-refereed


  • Melt crystallization
  • Pastillation
  • Raman spectroscopy
  • Self-coating


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