Application of derivative-differential UV spectrophotometry and ratio derivative spectrophotometric determination of mephenoxalone and acetaminophen in combined tablet preparation.

A method is presented for the direct determination of mephenoxalone and acetaminophen in combined pharmaceutical dosage forms without prior separation. The first method, derivative-differential spectrophotometry, comprised of measurement of the difference absorptivities derivatized in the first order (deltaD1) of a tablet extract in 0.1 N NaOH relative to that of an equimolar solution in methanol at wavelengths of 289.6 and 252.6 nm respectively. The second method is based on ratio derivative spectrophotometry. The amplitudes in the first derivative of the ratio spectra at 233.5 and 288.9 nm were selected to determine mephenoxalone and acetaminophen in the mixture. The proposed methods, which give thoroughly comparable data, are simple and rapid, and allow one to obtain precise and accurate results.