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We investigated the dual retention mechanism in thin-layer chromatography taking place on three stationary phases of different polarity (C-18, plain silica gel and DIOL) and using binary mobile phases composed of acetonitrile as the main component and water, or methanol as a modifier. As the test analytes, we selected a set of 12 compounds of pharmaceutical importance and considerably different chemical structure, i.e. the imidazoline and serotonin receptor ligands, and their related compounds. Retention of each analyte in each investigated chromatographic system was determined in a wide enough range of the mobile phase composition, with volume fraction of the mobile phase modifier ranging from 0.10 to 0.90. Calculation of the exact turning point values as a proof of occurrence of the reversed-phase hydrophilic interaction chromatography (HILIC/RP) retention mechanism was based on the multimodal retention model. The dual retention mode was described with the use of the volume fraction of the mobile phase modifier, the total polarity and the total solubility models. For the DIOL, C-18 and silica gel stationary phase, the dual (HILIC/RP) retention mechanism was confirmed. In the case of the DIOL stationary phase and acetonitrile/methanol mobile phase, the observed retention mechanism was more complicated than the dual HILIC/RP one. [ABSTRACT FROM AUTHOR]

The aim of this study was to develop a novel reversed-phase high-performance liquid chromatography (RP-HPLC) method for efficient separation of ivabradine and its 11 impurities. Similar polarity of impurities in the sample mixture made method optimization challenging and accomplishable only when different chemometric tools, such as principal component analysis (PCA), Box–Behnken design (BBD), and desirability function as a multicriteria approach, were employed. The presence of 3 positional isomers (impurities III, V, and VI), keto–enol tautomerism of impurity VII, and diastereoisomers of impurity X made separation of this complex mixture even more challenging. Chromatographic retention parameters obtained with the mobile phase consisting of 30 mM phosphate buffer and acetonitrile (80:20, v/v) on four different RP-HPLC columns at varying pH values (3.0, 4.0, and 5.0) were subjected to the PCA analysis to select the column with the most appropriate selectivity. Then the column temperature, pH of the aqueous component of mobile phase, phosphate buffer molarity and the organic solvent content in the mobile phase were estimated employing BBD. Valid and reliable mathematical models towards resolution of twelve critical peak pairs were obtained. After determination of the desirability making criteria for all responses, desirability functions were established and used in optimization. The proposed optimal chromatographic conditions included the Zorbax Eclipse Plus C18 chromatographic column (100 × 4.6 mm, 3.5 μm), the column temperature of 34 °C, the mobile phase flow rate of 1.6 mL min−1 and the UV detection at 220 nm. The mobile phase consisted of the 28 mM phosphate buffer at pH 6.0 and acetonitrile (85:15, v/v). Separation of one pair of positional isomers was not achieved, so methanol was added to the organic part of mobile phase in small increments with the optimal ratio of methanol to acetonitrile 59:41, v/v. The overall organic component of the mobile phase also increased to 18%, accelerating the chromatographic analysis. [ABSTRACT FROM AUTHOR]

The retention behavior of ivabradine, its 11 related compounds, diltiazem and verapamil has been examined by thin-layer chromatography using non-polar stationary phase (RP-18) and the following mobile phases: methanol-6.25% aqueous ammonia, tetrahydrofuran - 6.25% aqueous ammonia, and also polar stationary phase (silica gel) with tetrahydrofuran – 6.25% methanolic ammonia as mobile phase. In the examined chromatographic systems, linear relationships were established between the retention coefficients, RM0 and m, and molecular properties of the investigated antiarrhythmic drugs. The Quantitative Structure Retention Relationship (QSRR) modeling was performed with use of the stepwise multiple linear regression, in order to select the most important molecular properties which influence the retention behavior. The developed models revealed that apart from lipophilicity also the molecular volume (V), and the hydrogen bond basicity (B) of the tested compounds are the most important for the retention behavior in the examined chromatographic systems. [ABSTRACT FROM AUTHOR]

The chromatographic behavior of 16 alpha adrenergic and imidazoline receptor ligands has been studied by reversed-phase thin-layer chromatography (RP-TLC) on RP-18 and CN stationary phases. Retention constantwas determined for all tested compounds in three different chromatographic systems: methanol–water/RP-18, tetrahydrofuran–ammonia-water/RP-18, and tetrahydrofuran–ammonia–water/CN. Good correlations between determined hydrophobic parametersand calculated log P values were obtained for the system tetrahydrofuran–ammonia–water on both RP-18 and CN stationary phases. Experimentally obtainedvalues and computed molecular parameters of the examined compounds were further used for the quantitative structure–retention relationship (QSRR) study, in order to determine the most important properties governing retention. The QSRR modeling was performed with use of the partial least squares regression, and predictive performances of the developed QSRR models were tested by use of the cross-validation and external test set prediction. The created models revealed that apart from lipophilicity, constitutional descriptors, the amount of van der Waals surface area having a property P (P_VSA-like descriptors), and hydrogen bonding properties of the tested compounds were important for the retention behavior in the RP-TLC systems. [ABSTRACT FROM AUTHOR]

A SPE-HPLC-UV method for determination of moclobemide and its major metabolites, Ro 12-5637 and Ro 12-8095, in human plasma had been developed previously and its selectivity was evaluated against the most frequently coadministered drugs. The objective of the present work was to develop a quantitative structure retention relationship (QSRR) model capable of providing good predictions of chromatographic behaviour of other related potentially interfering drugs, based on the previously generated data, in order to further improve the clinical applicability of the existing method. Moreover, the most critical factors affecting SPE and chromatographic separations of moclobemide and its metabolites were evaluated and discussed, taking into account molecular properties of the analyzed compounds. [ABSTRACT FROM AUTHOR]

In order to improve the chromatographic resolution (Rs) with a good analysis time, experimental designs were applied for multivariate optimization of the experimental conditions of an isocratic reversed phase high performance liquid chromatographic (RP-HPLC) method used for the simultaneous determination of seven 2-arylimidazoline derivatives, acting as vasoconstrictors and antihypertensives. Optimal conditions for the separation of the seven 2-arylimidazolines were obtained using a mixture of acetonitrile-triethylamine phosphate buffer (pH 4.0; 25 mM) (30:70, v/v) as mobile phase at 25°C. Here the 23 full factorial experimental design was employed to optimize RP-HPLC separation of the 2-arylimidazolines. The suggested RP-HPLC method is applicable for routine analysis of the 2-arylimidazoline derivatives under the same chromatographic conditions, which can shorten the time and the costs of the analysis as well. Detailed description of the method development and optimization given in this paper will enhance the reproducibility of the established experimental conditions and simplify the process of some future methods developments. [ABSTRACT FROM AUTHOR]