Application of the First Derivative Absorption Spectrum-Shift-Length Method to the Simultaneous Determination of Binary Mixture.

The FDAS-SL method, which is a means of measuring the shift-length (SL, nm) of the maximum absorption wavelength of a drug by utilizing the first derivative absorption spectrum (FDAS), was used in the simultaneous spectrophotometric determination of binary mixtures. This method utilized the shift of the absorption spectrum of a drug at surfactant concentration above the critical micelle concentration. The mixed molar ratio is obtained from the shift-length, and each concentration of drug is calculated by Beer's law. The technique is applicable to binary mixed systems such as the methylparaben-propylparaben mixture which show similar absorption spectra, and gave accurate results.