Quantitative analysis of the active tablet ingredient by powder X-ray diffractometry.

A powder X-ray diffraction technique has been developed for the quantitative analysis of the active ingredient in intact tablets. Two model drugs were used: lithium carbonate (LC) and carbamazepine (CBZ). Mixtures containing various weight fractions of each drug and microcrystalline cellulose were compressed into tablets and the integrated intensities of several diffraction lines of each were used for quantitative purposes. The ratio of the integrated intensity of these lines in tablets, made from mixtures of drug and microcrystalline cellulose, to the intensity of the same lines in tablets made from only drug was calculated as a function of the weight fraction of the drug in the mixture. These ratios were also experimentally determined and the relative error in the determination of LC was less than 12%. CBZ tablets containing starch were also prepared. In the CBZ tablets containing microcrystalline cellulose or starch, the relative error in the determination of CBZ was less than 10% only when the weight fraction of CBZ in the tablets was greater than or equal to 0.4.