Combining the isoabsorptive point in the ratio spectrum and the smart ratio difference methods for a single step determination of compounds with overlapped spectra.

A new method significantly advantageous over the conventional spectrophotometric methods regarding simplicity, minimal data processing and applicability was developed. The new method is based on the fact that isoabsorptive points whenever present in an absorption spectrum will be retained even after division by a one component as a divisor in the ratio spectrum, in addition to a smart modification of the conventional ratio derivative and ratio subtraction methods. This modified method though simpler, enabled wider range of applications. The proposed method was applied for the analysis of brimonidine and timolol in laboratory prepared mixtures with mean percentage recoveries 100.64 ± 1.10 and 100.96 ± 1.16, respectively, and in their pharmaceutical formulation with mean percentage recoveries 100.88 ± 0.34 and 100.84 ± 0.72, respectively. The suggested method was validated according to USP guidelines and can be applied for routine analysis in quality control laboratories.