Thin layer chromatography of some statins in aqueous organic mobile phases modified with buffer solutions

The influence of a number of factors on the chromatographic properties of statins (atorvastatin, rosuvastatin, simvastatin) in normal-phase and reverse-phase chromatography modes has been studied by the method of the thin-layer chromatography (TLC) in order to select the most effective analytical systems for the total and separate determination of statins in pharmaceuticals. The study has been performed by ascending TLC on commercial plates with polar, weakly polar, and nonpolar phases. Efficiency and selectivity of chromatographic separation of statins have been established: the nature of the stationary phase (SF), the nature of the mobile phase (MF), the nature and concentration of the organic solvent of the mobile phase, the ionic strength of the solution. It has been revealed that the most effective SF are the reverse-phase plates RP-18, on which statins are separated with a high value of the number of theoretical plates (N) and the lowest value of the height of the equivalent theoretical plate (H). From organic solvents, the aprotic solvent acetonitrile turned out to be effective, which in the MF of the acetonitrile –water composition (70:30) gives the best results of chromatographic separation of statins. It has been found that with an increase in the ionic strength of the solution in the range of 0.1–1.5 mol (KCl), the mobility of statins changes slightly, which is accompanied by a significant blurring of chromatographic zones and deterioration of statin separation, and therefore no strong electrolyte was introduced in further studies. Binary mixtures of atorvastatin and simvastatin have been separated under selected optimal conditions. It has been found that the greatest selectivity of separation is observed in the MF acetonitrile – phosphate buffer (70:30) at pH 3. Quantitative determination of atorvastatin in «Atorvastatin-OBL», «Liprimar» and «Tulip» drugs has been carried out to optimize the chromatography conditions. The correctness and reliability of the determination has been established using the standard drug atorvastatin, Sr did not exceed 0.01–0.02.