Yulia Polyakova

Application of ionic liquids as mobile phase modifier in HPLC

Ionic liquids are receiving an upsurge of interest as ‘green’ solvents; primarily as replacements for conventional media in chemical processes. Although ionic liquids are rather “young” modifier, their great potential in high-performance liquids chromatography (HPLC) has already been demonstrated. This review presents an overview of the applications of ionic liquids as mobile phase modifiers in HPLC.

Effect of Concentration of Ionic Liquid 1‐Butyl‐3‐Methylimidazolium, Tetrafuoroborate, for Retention and Separation of Some Amino and Nucleic Acids

Abstract In this paper, three nucleic acids such as cytosine, cytidine, and thymine and two amino acids, such as D‐tryptophan and N‐carbobenzyloxy‐D‐phenylalanine, were chromatographed using ionic liquid as an additive for the mobile phase in high performance liquid chromatography (HPLC). Ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafuloroborate ([BMIm]+ [BF4]−), was used. The nucleic acid eluent was 5 vol. % of the modifier (methanol:acetonitrile=95:5 (vol. %)), in 10 mM of sodium phosphate monobasic, with addition of 0.5, 2.0, and 4.0 mmol/L of ionic liquid. Separation of nucleic acids was obtained on a commercially available octadecyl silica column (4.6×150 mm i.d., and particle size 5 µm). In the case of D‐amino acids, the mobile phase was 65% methanol in water, with additions of 0.5, 1.0, 2.0, 8.0, 12.0, and 15.0 mmol/L of ionic liquid. The experiments were performed on a stainless steel column, 3.9×300 mm i.d., and particle size 15 µm, packed with octadecyl‐bonded silica at the laboratory. Effects of the concentration of ionic liquid for retention and separation of some nucleic and amino acids were discussed. The results showed the potential application of ionic liquid as a mobile phase additive in liquid chromatography.

Linear Regression Based QSPR Models for the Prediction of the Retention Mechanism of Some Nitrogen Containing Heterocycles

Abstract This study evaluates retention factors of 29 nitrogen containing heterocycles using QSPR models in liquid chromatography. Some structure properties, such as the molecular connectivity indices (0χ∼5χ), Wiener index (W), Kier flexibility index (φ), Harary index (H), Balaban indices (JX∼JY), and Zagreb indices (M 1∼M 2) were obtained by theoretical molecular descriptors derived from information of chemical structures of substances. The relationship between the chromatographic retention factors and the structure descriptors were predicted using a mathematical method, regression analysis. All substances were divided into five groups based on similar structures with functional groups. For each group, the simple linear regression between each structural index and the retention factor showed good regression coefficients. The linear regression between retention factor and various orders of connectivity indices showed good regression coefficient (r 2=0.8∼1) and, with multiple structural properties, showed ...

Retention factors and resolutions of amino benzoic acid isomers with some lonic liquids

Ionic liquids in the form of organic salts are being widely used as new solvent media. In this paper three positional isomers,o-amino benzoic acid,m-amino benzoic acid, andp-amino benzoic acids were separated with four different ionic liquids as mobile phase additives using high performance liquid chromatography (HPLC). The following ionic liquids were used: 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4]), 1-ethyl-3-methylimidazolium methylsulfate ([EMIm][MS]), and 1-octyl-3-methylimidazolium methylsulfate ([OMIm][MS]). The effects of the alkyl group length on the imidazolium ring and its counterion, and the concentrations of the ionic liquids on the retention factors and resolutions of amino benzoic acid isomers were tested. The results of the separations with ionic liquids as the eluents were better than those without ionic liquids. Excellent separations of the three isomers were achieved using 2.0≈8.0 mM/L [OMIm][MS] and 1.0≈8.0 mM/L [EMIm][MS] as the eluent modifiers.

Evaluation of Predictive Retention Factors for Phenolic Compounds with QSPR Equations

Abstract Evaluation of predictive retention factors of phenolic compounds from their physico‐chemical and structural properties can be made successfully in terms of quantitative structure–property relationships (QSPR) equations. The relationships of correlation between retention factors of sixteen phenolic compounds reported in the bibliography and various descriptors, including binding energy (E b), hydrophobicity (log P), hydrophilic–lipophilic balance (HLB), molecular refractivity (MR), polarizability (α), water solubility (log S), and wiener index (w) were established. The empirical equations were expressed in a linear and multiple‐linear form. The results of theoretical calculations are in agreement with the experimental data. The empirical equation can be applied for prediction of the various chromatographic properties, including identification of the substances with a similar structure.

HPLC of Some Polar Compounds on a Porous Graphitized Carbon HypercarbTM Column

Abstract The chromatographic performance of a Hypercarb™ stationary phase was studied by using benzene, indene, and some polar compounds as probes. The effect of the mobile phase composition on the retention of the substances was investigated. The influence of organic modifier acetonitrile on the retention was also studied and interpreted on the basis of intermolecular interactions. Significant retention of these molecules was observed in acetonitrile‐water eluents. The multitype nature of interaction of the solute on the reversed phase surface and its charge inducted interactions with polar molecules were responsible for significant retention of these substances. Separation on the Hypercarb™ column showed that the retention order of solutes generally does follow their polarity order. The dispersion and orientational interactions undoubtedly influence, but do not solely determine, the elution order of solutes. According to the chromatographic data, it can be concluded that the retention of the investigated substances is defined by the interaction of the polarized or polarizable functional groups in the samples with a graphite surface (charge‐inducted interactions), which is termed in the literature as the “polar retention” by Hypercarb™.

Retention‐Eluent Composition Relationships of Some Polar Compounds with Imidazolium Ionic Liquid Modifiers in RP‐HPLC

Abstract Four commonly known equations, two linear (Soczewinski and Langmuir‐type) and two quadratic, have been applied for investigation of the influence of imidazolium ionic liquids modifiers on the retention eluent composition relationships in reversed‐phase high performance liquid chromatography. In this study, three ionic liquids (1‐butyl‐3‐methylimidazolium tetrafluoroborate, 1‐ethyl‐3‐methylimidazolium methylsulfate, and 1‐octyl‐3‐methylimidazolium methylsulfate) were evaluated as mobile phase modifiers. In the experiment, nine solutes belonging to three chemical classes, and namely: nucleic compounds (uridine 5′‐monophosphate, inosine 5′‐monophosphate, guanosine 5′‐monophosphate, and hymidine 5′‐monophosphate disodium salts), nitrogen containing heterocycles (guanine and hypoxanthine), and amino benzoic acids (orthro‐, meta‐, and para‐isomers of amino benzoic acid) were tested. Evaluation of models of chromatographic retention was performed and discussed. The best correlations were achieved employing Langmuir‐type and Soczewinski equations.

Quantitative Structure-Retention Relationships Applied to Reversed-Phase High-Perfromance Liquid Chromatography

A quantitative structure-retention relationships (QSRR) approach, as one of the all-important areas in modern chemical science, gives knowledge that is practical and necessary for drug design, combinatorial, and medicinal chemistries. A QSRR derived by means of various statistical procedures are reviewed from the viewpoint of identifying retention affecting various factors and understanding the mechanism of chromatographic separations. A brief summary of the theoretical background of QSRR is followed by presentation of reversed-phase high performance liquid chromatographic (RP-HPLC) separation theories of applications to the reported QSRR. Structural and physicochemical descriptors derived by RP-HPLC are discussed in relation to retention factors with special accent on properties of reversed-phase materials. Reported QSRR models are critically reviewed, bearing in mind their statistical predictability physical meaning. Information on retention mechanisms is briefly analyzed also. It is concluded that QSRR employing molecular descriptors expected to model fundamental intermolecular interactions. A QSRR studies are already demonstrated their great potential in most essential areas of contemporary chemistry. A quantity of scientific publications steadily grows from year to year, this implyies that the QSRR enormous advantage and potential in chemistry, biology, and pharmacology.

Analysis of linear regressions applied to water-methanol eluents modified with ionic liquid

Abstract Five equations, two linear (Soczewinski and Langmuir‐type) and three multiple linear have been applied for investigation of the influence of 1‐butyl‐3‐methylimidazolium tetrafluoroborate ionic liquid modifier on the retention eluent composition relationships in reversed‐phase high performance liquid chromatography. In the experiment, five solutes belonging to amino acids, namely N‐carbobenzyloxy‐D‐phenylalanine, D‐tryptophan, and orthro‐, meta‐, and para‐isomers of amino benzoic acid were tested. Statistical evaluation of models of chromatographic retention was performed and discussed. This study shows that Soczewinski and Langmuir‐type equations are able to describe chromatographic retention of molecules which do not form stable ions in the aqueous, relatively precisely. At the same time, these models are not applicable for the description of N‐CBZ‐D‐phenylalanine retention, which exists in the water solution as anion and more complex models, considering that interactions between ionizable sample and eluent are required. Multiple linear regressions with two variables (methanol and ionic liquid modifier contents) improve significantly the description of N‐CBZ‐D‐phenylalanine retention.