3RD-DERIVATIVE SPECTROPHOTOMETRIC SIMULTANEOUS DETERMINATION OF VITAMIN-A AND VITAMIN-E IN SOME PHARMACEUTICAL PREPARATIONS

A third-derivative spectrophotometric method was developed for the simultaneous determination of vitamins A and E in the presence of one another without prior separation. Third-derivative spectra of sample solutions in isopropyl alcohol were scanned between 270 and 360 nm. Because of the difference in the molar absorptivities of the two vitamins, different d3A/d-lambda-3 ordinate scales were used. For vitamin E, the peak amplitude in the derivative spectrum was measured at 290 from peak to base (zero crossing, 3D290). For vitamin A, the largest amplitude in the derivative spectrum was measured between the minimum at 308 nm and its maximum at 314 nm (3D308,314). The value of 3D for each compound was not affected by the presence of the other compound, and the calibration graph was linear in the ranges of 3-15-mu-g ml-1 vitamin A (r = 0.9999) and 7-35-mu-g ml-1 vitamin E (r = 0.9999). The method was designed to allow a single-unit assay for the normal dosage used. The method was successfully applied to commercial soft gelatin capsules and chewable tablets containing the two vitamins.