User-Friendly HPLC Method Development and Validation for Determination of Enalapril Maleate and Its Impurities in Enalapril Tablets.

The official method for the determination of Enalapril Maleate and its related substances in European Pharmacopoeia (EP) is a gradient liquid chromatographic method. The method used styrene-divinylbenzene copolymer column, mobile phase buffer pH 6.8 and column oven temperature 70°C. In this method, the separation between main component Enalapril and Ph. Eur. Imp-A was not completed hence the achieving system suitability requirement is a tough task and it requires quite often adjustment in chromatographic parameters. Moreover, column oven temperature 70°C is not user friendly to HPLC instruments and users. In this study, several changes were introduced to the method in order to improve the separation, peak shapes and to overcome the column oven temperature. A new user-friendly stability-indicating RP-HPLC method was developed for Enalapril related substances analysis. The developed method uses a ZORBAX Eclipse XDB-C18 column with column oven temperature at 55°C and mobile phase containing acetonitrile and a phosphate buffer at pH 3.0. The method is capable of separating all the known impurities with resolution more than 3.5, which is much better than that obtained with the existing monograph methods. The optimized method was validated and demonstrated to have acceptable specificity, sensitivity, linearity, accuracy, precision, robustness, solution stability and equivalency to the EP method. The developed method proved to be applicable to a wide number of C18 reversed-phase columns. In addition, the Enalapril assay method also presented with 20 min run time.

Development and validation of a simple, sensitive, selective and stability-indicating RP-UPLC method for the quantitative determination of ritonavir and its related compounds.

A simple, sensitive, selective and reproducible stability-indicating ultra-performance liquid chromatographic method was developed for the quantitative determination of degradation products and process-related impurities of Ritonavir in a pharmaceutical dosage form. Chromatographic separation was achieved on a polar embedded Waters Acquity BEH Shield RP18 (100 × 2.1 mm, 1.7 µm) column thermostated at 50°C under gradient elution by using a binary mixture of potassium dihydrogen phosphate (0.01 M, pH 3.5) and acetonitrile at a flow rate of 0.5 mL/min. Chromatogram was monitored at 240 nm using a photodiode array detector. The drug and its related impurities are eluted within 20 min. To prove the stability-indicating power of the method, the drug was subjected to hydrolytic (acid, alkaline and water), oxidative, photolytic and thermal stress conditions. The unknown degradants were identified by the LC-MS-MS method, which revealed protonated molecular ion peaks [M + H](+) at m/z 551.40 for hydrolytic degradants, and m/z 737.60 and m/z 753.40 for photolytic degradants. A plausible mechanism for the formation of degradation and process impurities was proposed. The performance of the method was validated according to the International Conference on Harmonization guidelines.