A new simple spectrophotometric method was developed for the simultaneous determination of drugs with interfering spectra in binary mixtures without previous separation.The new method is based on a simple modification for the ratio subtraction method.This modification enabled wider range of application.The proposed ratio difference method was applied for the determination of brimonidine and timolol in laboratory prepared mixtures with mean percentage recoveries 100.40±2.29 and 101.23±1.30 respectively,and in their pharmaceutical formulation with mean percentage recoveries 101.08±0.44 and 100.66±0.52 respectively.The suggested ratio difference method was validated according to USP guidelines and can be applied for routine quality control testing.
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