Colorimetric assay of quinine and quinidine in raw materials, formulations, and biological fluids.

The two characteristic erythroquinine and thalleioquin tests for quinine and quinidine were studied to optimize the experimental conditions for quantitative analysis. Both methods were quantitatively sensitive for either quinine or quinidine in a concentration range of 0.1--10 microgram/ml with the erythroquinine method and of 3--50 microgram/ml with the thalleioquin method. A TLC--colorimetric method also is described for the assay of quinine and quinidine in the presence of cinchonine, cinchonidine, and other cinchona alkaloids. The results were compared with those obtained with a spectrophotometric method.