Hybrid micellar liquid chromatography separation of brimonidine tartrate and brinzolamide. Retention study and quantification in fixed dose ophthalmic suspensions

• Brimonidine and brinzolamide have been determined in ophthalmic suspensions. • We used micellar liquid chromatography and low volumes of organic solvents were employed. • A chemometric strategy has been used to study the retention mechanism. • The method was validated by the guidelines of the ICH. • It was green, cost-effective, safe, easy-to-conduct, with high sample throughput and reliable. Brinzolamide/brimonidine 1%/0.2% fixed-dose combination medication is an ophthalmic suspension widely used to treat eye disorders related to elevated intraocular pressure. An analytical procedure based on hybrid micellar liquid chromatography has been developed to quantify the active components in pharmaceutical preparations. Samples were diluted, up to a target concentration of 50 mg/L brinzolamide and 10 mg/L brimonidine tartrate, in a mixture of methanol and mobile phase by stirring and ultrasonication, filtered and directly injected without an extraction step. The drugs were resolved from the matrix using a mobile phase of 0.10 mol/L sodium dodecyl sulfate − 4 % 1-butanol – 0.01 M sodium dihydrogen phosphate, with a pH adjusted to 3 by adding drops of hydrochloric acid solutions. running at 1 mL/min under isocratic mode through a C18 column. Detection UV absorbance wavelength was set to 250 nm. A theoretical study on the retention mechanism was calculated and the constants of the partition equilibria occurring in the column were calculated. The method was successfully validated by the guidelines of the International Conference on Harmonization in terms of: calibration range (from 0.1 to 2 times the target concentration), linearity (r 2 > 0.995), trueness (98.3–102.6 %), precision (<2.2 %), limit of detection, limit of quantification (under the lowest level of calibration) and robustness. The procedure was applied to commercial formulations. The method was found cost-effective, easy-to-conduct, safe, ecofriendly (low quantity of hazardous reagents were used) and with a high sample throughput, which makes it suitable for routine analysis in pharmaceutical quality control. On the other hand, we deduced this was mainly driven by electrostatics, and the surfactant had more influence in elution strength than the organic modifier.