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Quantification of active substance in drug by Rietveld analysis

Marta Łaszcz 


The X-ray powder diffraction has variety applications in the pharmaceutical industry. The most popular is a polymorphs diagnostic of an active substance (API - Active Pharmaceutical Ingredient). If API has more than one crystalline form there is a risk that during following steps like: synthesis, milling, formulation and storage an undesirable form appears. For this reason powder diffraction is a main tool for qualitative and quantitative analysis.

The aim of this work was to apply the quantitative Rietveld analysis for an evaluation of API in few commercial drugs. For example, VFEND (Pfizer) tablets contain voriconazole as API. The inactive ingredients include: lactose monohydrate, pregelatinized starch, croscarmellose sodium, povidone, magnesium stearate. Voriconazole1, lactose2 and magnesium stearate are crystalline. The others ingredients are amorphous or semi-crystalline. Qualitative analysis detected only voriconazole and lactose. Relative phase amounts, in weight percent, are following: voriconazole 35.63%, lactose 47.39% and amorphous 16.98% (figure below). The calculated voriconazole content is close to the real quantity which is equal 30%.
Measurement time 60min. GOF 5.86, Rexp 1.15, Rwp 6.74, Rp 5.31.

Fig. Quantitative Rietveld analysis of VFEND.

1) K. Ravikumar, B. Sridhar, K. D. Prasad, A. K. S. B. Rao (2007) Acta Crystallogr., Sect. E.: Struct. Rep. Online, 63, o565,
2) J. H. Noordik, P. T. Beurskens, P. Bennema, R. A. Visser, R. O. Gould (1984) Z. Kristallogr., 168, 59.

The X-ray measurements were undertaken in the Structural Research Laboratory at the Chemistry Department of the University of Warsaw.


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Presentation: Poster at 11th European Powder Diffraction Conference, Poster session, by Marta Łaszcz
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-06-19 09:33
Revised:   2009-06-07 00:48