Determination of binary mixtures of analgesic and spasmolytic drugs in pure and dosage forms by derivative spectrophotometry

Abstract

Binary mixtures of dipyrone and pitophenone hydrochloride are assayed by zero-crossing second- and third-derivative spectrophotometry and by ratio-spectra first- and second-derivative spectrophotometry. In the first method, calibration plots are linear at 266.5 and 302.5 nm (dipyrone, second derivative), and 257 and 286 nm (pitophenone second derivative) and 242 and 278.3 nm (dipyrone third derivative), and 228.5 and 300 nm (pitophenone, third-derivative). By the second method, lines of regression are linear at 235 and 262 nm (dipyrone, first derivative), and 229.5 and 288.5 nm (pitophenone, first-derivative), and 249.7 and 268 nm (dipyrone, second derivative), and 280.5 and 300 nm (pitophenone, second-derivative). In all methods calibration curves follow the Beer's law up to 40 μg/ml of each drug. LOD and LOQ values were calculated. The developed derivative spectrophotometric methods were applied to laboratory mixtures and to vials for these drugs. The procedures are simple, rapid, and did not require any preliminary separation or treatment of the samples.