A comparative study of two novel validated spectrophotometric techniques for resolution of four-component mixtures with severely overlapping spectra.

Two new smart spectrophotometric methods are developed and validated for the determination of the quatertnary mixture of paracetamol (acetaminophen), diphenhydramine, p-aminophenol, and N-oxide degradate of diphenhydramine. Method A is the novel triple divisor ratio difference method, where the triple divisor ratio spectrum of the component of interest shows a significant amplitude difference at two selected wavelengths where the three interfering substances are used as triple divisor and give constant amplitude all over the spectrum. The triple divisors are normalized spectra of tertiary mixtures containing 40 μg/mL of each of the 3 interfering components. The selected wavelengths are 256-290 nm, 220-230 nm, 230-245 nm and 275-260 nm for the 4 components, respectively. Method B is double divisor - ratio difference-dual wavelength, where the double divisor ratio spectrum of the component of interest shows a significant amplitude difference at two selected wavelengths where two interfering substances are used as double divisor and give constant amplitude all over the spectrum, while the third one shows zero amplitude difference at these two selected wavelengths. The double divisors used are normalized spectra of diphenhydramine /N-oxide degradate of diphenhydramine binary mixture for both paracetamol and p-aminophenol and paracetamol/p-aminophenol binary mixture for both diphenhydramine hydrochloride and its N-oxide degradate. The double divisors binary mixtures contain 40 μg/mL of each component. The selected wavelengths are 243-233 nm, 223.8-270.2 nm, 237-250 nm and 265-234.6 nm for the 4 compounds, respectively. Both methods were successfully applied for the quantification of the four components in laboratory prepared quaternary mixtures and for the quantification of paracetamol and diphenhydramine hydrochloride in panadol night® tablets. The results obtained by the developed methods were compared with those obtained by the United State Pharmacopeial method for the analysis of paracetamol and diphenhydramine, where no significant differences were found.