Simultaneous determination of drugs with different physicochemical properties necessitates thorough research and careful selection of high‐performance liquid chromatography conditions. In the present study, various concepts of high‐performance liquid chromatography method development for this aim have been discussed. Moreover, the work was motivated by the advantages of utilizing different chaotropic anions as a new promising approach to overcome the limitations of ion‐pairing agents commonly used for this purpose. Based on log P values, atorvastatin (log P = 6.36) and lisinopril (log P = –1.22) were chosen as representative examples for lipophilic and hydrophilic drugs, respectively. Several simple, economic, fast, and reliable high‐performance liquid chromatography methods were developed for their simultaneous analysis and are presented in a comparative manner, highlighting their advantages and limitations. Peak elution profile showed satisfying retentions and resolution about 3. Photo‐diode array calculations were exploited for identifying the molecules by their ultra‐violet spectra and peak purity, calculated and presented as rectangular‐shaped ratio grams. The linearity check showed excellent results and satisfactory system suitability parameters of both peaks. This confirms the investigation results and conclusions for the influence of the chaotropic salts on N‐containing molecules, by increasing their retentivities, and improving peak shapes, even on different quality columns without end‐capping and base‐deactivating of separation matrixes.

A fast, simple, accurate and robust reversed phase HPLC method for the simultaneous determination of two flavonoids, hesperidin and diosmin, in combined tablets was developed and validated. This method uses a short C8 column with dimensions of 75 mm × 4 mm with 5 µm particles thermostated at 30 °C, and a mobile phase composed of formic acid (pH 4.1 and 0.05%, V/V) and methanol (58:42, V/V), delivered at a flow rate of 1.2 ml/min, with UV detector signal monitoring at 280 nm and an injection volume of 5 µl. These chromatographic conditions yielded chromatograms with symmetric peaks of hesperidin, eluting at a ~2 min retention time, and diosmin, at a ~4.5 min retention time, with a total run time cycle of 6 min. The method validation parameters confirmed excellent values for accuracy, linearity and reproducibility. This method is suitable for routine analysis in pharmaceutical and food quality control laboratories.

New, fast, simple and mild conditioned High Performance Liquid Chromatography (HPLC) method for determination of atorvastatin and its 7 main specified impurities, as well as unspecified impurities that might possibly appear, was developed. Chromatographic runs last between 25 and 40 minutes, with simple stepwise gradient elution. The main accent in our method development strategy was focused on mobile phase, composed of simple binary system composed of phosphate buffer and acetonitrile, at pH 4.1, without use of tetrahydrofuran, ion-pair reagents, trifluoroacetic acid and other modifiers with high Ultraviolet (UV) cut-off like absorptive acetate or formiate buffers or amines. With our concept of mobile phase, different columns from myriad were tested, with different efficiency, dimensions and properties, which resulted in different separation efficiency and run time. The best results, concerning essential critical peak resolution, run time length including column preparation and equilibration and column backpressure, were achieved with: YMC C18 Triart 150mm x 4.6mm, 3µm (YMC America, Inc.), afterwards with Nucleodur 100-3-C18ec 250mm x 4.6mm, 3µm (Macherey-Nagel GmbH & Co., Germany), Waters Symmetry C18 250mm x 4.6mm, 5µm (Waters, USA) and Superspher C18e 125mm x 4mm, 4µm (Merck, Darmstadt, Germany). All this columns achieve excellent results regarding obligated critical resolution between atorvastatin impurity B and atorvastatin (according to European Pharmacopoeia),1 or in some cases between atorvastatin impurity B and atorvastatin impurity C, to be minimum about 1.5, in both cases.