A comprehensive method for meldonium analysis, based on a combination of magnetic solid-phase concentration of the analyte on magnetite nanoparticles modified with cetylammonium bromide (CTAB) cations and its subsequent analysis by thin-layer chromatography (TLC) were developed in the process of study. The influence of a number of factors on meldonium sorption was studied, namely: pH, sorbent mass, sorption and mixing times; optimal extraction conditions were determined. It was found that quantitative sorption proceeded in 20 min with a meldonium extraction degree of 88%. Ethanol was found to be an eluent to desorb the analyte by 95%. The calibration dependences plotted with and without concentration of meldonium were compared. It was established that the use of concentration on two mg of CTAB-modified nanomagnetite reduces the lower limit of the analyzed contents of meldonium in 25 ml of solution by 5 times.
The chromatographic behavior of atorvastatin, rosuvastatin and simvastatin in the presence of the main modifiers of the mobile phase: elution strength and buffer solution, has been studied by means of the reverse-phase high-performance liquid chromatography (HPLC) method. Optimal modification conditions have been found and their application for the determination of statins under study in the pharmaceutical preparations Atorvastatin-OBL, Liprimar and Tulip has been shown. The Sr value is 0.03. The relative determination error does not exceed 7%.
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.
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