SIMULTANEOUS QUANTIFICATION OF AN ENANTIOMER AND THE RACEMIC COMPOUNDOF IBUPROFEN BY X-RAY-POWDER DIFFRACTOMETRY

Purpose. An X-ray powder diffractometric method was developed for the simultaneous quantification of the relative amounts of the racemic com pound (+/-) of ibuprofen (I) and S(+)-ibuprofen (II), when they occur as a mixture. Method. The X-ray powder diffraction patterns of I and L I show pronounced differences. This formed the basis for the determina tion of the relative amounts of I and IT when they occur as a mixture. X-ray lines with d-spacings of 14.41 and 4.37 Angstrom were unique to I and II, respectively Mixtures containing different proportions of I and II were prepared which also contained lithium fluoride (III) as a n internal standard. Results. A linear relationship was obtained when the intensity ratio (intensity of the 4.37 Angstrom line of II/intensi ty of the 2.01 Angstrom line of III) was plotted as a function of the weight fraction of II in the mixture. Similar results were obtained in the case of I. Using these standard curves, the weight fractions of I and II in ''unknown'' mixtures were determined. The experimentally de termined analyte concentration ranged between 98 and 104% of the true value. The relative error in the analyses of individual samples was <1 0%. The minimum detectable weight fraction of I in II and II in I were 0.032 (3.2% w/w) and 0.034 (3.4% w/w), respectively. The minimum quan tifiable weight fractions were 0.136 for I and 0.112 for II. Since the X-ray diffraction patterns of S(+)-ibuprofen and R(-)-ibuprofen are i dentical, the conclusions drawn regarding mixtures of I and II will al so hold true in the quantitative analyses of mixtures of I and R(-)-ib uprofen.