APPLICABILITY OF BIVARIATE CALIBRATION ALGORITHM AND VIERORDT METHOD FOR SIMULTANEOUS DETERMINATION OF TIMOLOL MALEATE AND BRIMONIDINE TARTRATE IN THEIR BINARY MIXTURE AND PHARMACEUTICAL DOSAGE FORM

Three simple, rapid, sensitive, specific and economic spectrophotometric methods were developed and validated for simultaneous quantitation of timolol maleate (TM) and brimonidine tartarate (BT) in bulk powder and eye drops.  Vierordt’s and bivariate calibration algorithm spectrophotometric methods were developed for the simultaneous estimation of cited drugs in a binary mixture without previous separation.    In the simultaneous equation method (Vierordt’s), TM and BT were quantified using their absorptivity values at selected wavelengths 257 nm and 295 nm, respectively.  Also bivariate calibration procedure was successfully applied for simultaneous determination of both drugs.  Difference spectrophotometric method was also tried and showed high selectivity for BT determination without any interference from TM or eye drops additives.  The accuracy and reproducibility of the proposed methods were statistically validated by recovery studies.  The calibration curves were found to be rectilinear over the concentration ranges 5-85 μg/mL for TM in all methods. BT calibration curves were rectilinear over the concentration (2–35 μg/mL) in case of D₁ and Vierordt’s methods, while (5–35 μg/mL) in case of bivariate method at the previously mentioned wavelengths, in addition to (4-50 μg/mL) in case of difference spectrophotometry.  The proposed methods can determine different concentrations of bulk powder with satisfied mean percentage recoveries. The proposed methods are economic and rapid methods only a few minutes were required for the analysis. So, they can be used for routine analysis of both drugs in quality control laboratories.