Simultaneous determination of phenazopyridine HCl and trimethoprim in presence of phenazopyridine HCl impurity by univariate and multivariate spectrophotometric methods - Quantification of phenazopyridine HCl impurity by univariate methods.

Three univariate and two multivariate spectrophotometric methods were developed and subsequently validated to determine phenazopyridine HCl (PHZ) and trimethoprim (TMP) in the presence of 2,6-Diaminopyridine (2,6-DAP). The first univariate method depends on direct determination of phenazopyridine by measuring its absorbance at 412 nm and performed in concentration range of 1.00-10.00 μg/mL. Then the contribution of phenazopyridine is removed by dividing the mixture spectrum with PHZ divisor (5 μg/mL) after that the constant is mathematically subtracted and finally the generated spectrum is multiplied with the PHZ divisor. These steps eliminate PHZ contribution and the recovered spectrum is that of TMP and 2,6-DAP only where different methods can be applied to determine TMP and 2,6-DAP through this binary mixture spectrum. The first method to determine both components depends on measuring both TMP and 2,6-DAP through their first derivative (DD) spectra at 244.70 and 259.60 nm for TMP and 2,6-DAP, respectively with concentration ranges of 4.00-24.00 μg/mL TMP and 4.00-26.00 μg/mL 2,6-DAP. The second method depends on application of the isoabsorptive method which was used for TMP determination at its isoabsorptive point with 2,6-DAP at 242.64 nm with concentration range 1.00-20.00 μg/mL for TMP. The developed univariate methods were successfully applied to determine PHZ, TMP and PHZ impurity (2,6-DAP). Two multivariate methods were applied for determination of PHZ and TMP in presence of 2,6-DAP namely, Principle Component Regression (PCR) and Partial Least Squares (PLS). The results of the two models show that simultaneous determination of PHZ and TMP in presence of PHZ impurity can be performed in the concentration ranges of 6.00-14.00 μg/mL PHZ and 24.00-56.00 μg/mL TMP. All the proposed methods were successfully applied to analyze PHZ and TMP in pharmaceutical formulations without interference from the dosage form additives and the results were statistically compared with the reported method.