Development and Validation of a New LC Method for Analysis of Brimonidine Tartrate and Related Compounds

A novel liquid chromatographic method for analysis three potential impurities in brimonidine tartrate drug substance has been developed and validated. Efficient chromatographic separation was achieved on a C(8) column (250 mm x 4.6 mm, 5-mu m particles) with a simple mobile-phase gradient at a flow rate of 1.0 mL min(-1). Quantification was achieved by use of ultraviolet detection at 248 rim. Resolution between brimonidine tartrate and its three potential impurities was greater than 3.0. Regression analysis showed the r value (correlation coefficient) was > 0.999 for brimonidine and its three impurities. The method was capable of detecting all three impurities of brimonidine tartrate at levels below 0.07 mu g in a test concentration of brimonidine tartrate of 1.0 mg mL(-1) and for an injection volume of 10 mu L. A solution of brimonidine tartrate in acetonitrile-water 2:8 (v/v) was stable for 48 h. The drug was subjected to stress conditions as prescribed by the ICH. Degradation was found to occur slightly under oxidative stress conditions but the drug was stable to aqueous, acidic, and basic hydrolysis, and photolytic and thermal stress. The assay of the stressed samples was calculated relative to a qualified reference standard and the mass balance was found close to 99.8%. The method was validated for linearity, accuracy, precision, and robustness.