Novel spectrophotometric methods for simultaneous determination of timolol and dorzolamide in their binary mixture

•Two novel methods namely; absorbance subtraction (AS) and amplitude modulation (AM) methods were developed.•Six recently well established spectrophotometric methods (SRS, RD, RS, EXRS, CM and MCR) were applied.•The proposed methods are very simple, accurate, precise.•They do not require any sophisticated apparatus or computer programs.

Two smart and novel spectrophotometric methods namely; absorbance subtraction (AS) and amplitude modulation (AM) were developed and validated for the determination of a binary mixture of timolol maleate (TIM) and dorzolamide hydrochloride (DOR) in presence of benzalkonium chloride without prior separation, using unified regression equation. Additionally, simple, specific, accurate and precise spectrophotometric methods manipulating ratio spectra were developed and validated for simultaneous determination of the binary mixture namely; simultaneous ratio subtraction (SRS), ratio difference (RD), ratio subtraction (RS) coupled with extended ratio subtraction (EXRS), constant multiplication method (CM) and mean centering of ratio spectra (MCR). The proposed spectrophotometric procedures do not require any separation steps. Accuracy, precision and linearity ranges of the proposed methods were determined and the specificity was assessed by analyzing synthetic mixtures of both drugs. They were applied to their pharmaceutical formulation and the results obtained were statistically compared to that of a reported spectrophotometric method. The statistical comparison showed that there is no significant difference between the proposed methods and the reported one regarding both accuracy and precision.

Graphical abstractZero-order spectra of 40 μg/mL of DOR (—) and TIM (…), separately in methanol, and binary of a mixture of DOR and TIM, 20 μg/mL of each (- - -) and their ratio spectra using the spectrum of TIM (1 μg/mL) as a divisor.Figure optionsDownload full-size imageDownload as PowerPoint slide