Determination of the Relative Amounts of α-carbamazepine and β-carbamazepine in a Mixture by Powder X-Ray Diffractometry

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Abstract
A powder X-ray diffraction technique has been developed to quantify the relative amounts of α-carbamazepine (A) and β-carbamazepine (B) when they occur as a mixture. The theoretical basis of this technique was developed in 1948 by Alexander and Klug (Anal. Chem., 20:886-889). The powder X-ray diffraction patterns of A and B revealed that the line with d-spacing of 10.1 Å was unique to A. The ratio of the integrated intensity of the 10.1 Å line in a mixture of A and B, to the intensity of the 10.1 Å line in a sample consisting of only A, was calculated as a function of weight fraction of A in the mixture. These ratios were also experimentally determined, and there was a good agreement between the theoretical and experimental intensity ratios. The particle size of the samples, the sample preparation technique and the experimental conditions were controlled so as to eliminate the major sources of error in powder X-ray diffractometry. In order to minimize preferred orientation of the particles, a sample holder was specially fabricated.

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