The Spectrophotometric Multicomponent Analysis of a Ternary Mixture of Paracetamol, Aspirin, and Caffeine by the Double Divisor-Ratio Spectra Derivative Method

Double divisor-ratio spectra derivative method based on the spectrophotometric data was developed for the simultaneous analysis of a ternary mixture containing paracetamol, aspirin, and caffeine, without prior separation. This method is based on the use of the derivative of the ratio spectrum obtained by dividing the absorption spectrum of the ternary mixture by a standard spectrum of a mixture of two of the three compounds in the title mixture. The concentrations of three compounds in their mixture are determined by using their respective calibration graphs which are obtained by measuring the amplitude at either the maximum or minimum wavelengths selected. The selected wavelengths for determination of aspirin, caffeine, and paracetamol are 241.5, 256, and 258.5？nm, respectively. All of the solutions adjusted to pH 11 before recording the spectra in the range of 220 to 320？nm. Also, the mathematical explanation of the procedure is illustrated. The method was applied for the assay of Excedrin containing paracetamol, aspirin, and caffeine. 1. Introduction For the simultaneous determination of two or more active compounds in the same mixtures without a separation step, several spectrophotometric methods, such as classical derivative spectrophotometry [1–4], Vierordt’s method [5] and its modified version [6], orthogonal function method [7], dual wavelength spectrophotometry [8–10], pH-induced differential spectrophotometry [11], the least square method [12], the multicomponent analysis program [13, 14] and a method, and multiwavelength linear regression analysis (MLRA) which was referred to by Blanco and co-workers [15] have been utilized. Salinas et al. [16] and Nevado et al. [17] developed two methods for the resolution of two or more compounds in mixtures by ratio spectra derivative spectrophotometry and the derivative ratio spectra-zero crossing method. Salinas’ method is based on the use of the derivative of the ratio spectra for a binary mixture. The absorption spectrum of the mixture is divided by the absorption spectrum of one of the compounds, and the first derivative of the ratio spectrum is obtained. The concentrations of active compounds are then determined from the calibration graphs obtained by measuring the amplitudes at points corresponding to the minimum or maximum wavelengths. In Berzas Nevado’s method, the simultaneous determinations of three compounds in ternary mixtures are based on the measurements of the amplitude at the zero crossing points in the derivative spectrum of the ratio spectra. In the present research, a sensitive,