0000000000190762
AUTHOR
S. López-grío
Influence of the addition of modifiers on solute-micelle interaction in hybrid micellar liquid chromatography
In reversed-phase micellar liquid chromatography (MLC) organic modifiers are usually added to the mobile phase to modify the eluent strength and to increase the efficiency of the chromatographic peaks. The effect of the modifiers methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, acetonitrile and tetrahydrofuran on the critical micelle concentration (cmc) of the anionic surfactant sodium dodecylsulphate (SDS) has been studied to enable understanding of the interactions between solute, micelles and bulk liquid in such hybrid eluents. Methanol, acetonitrile and tetrahydrofuran increased thecmc, whereas the other alcohols reduced its value. For butanol and pentanol, which partition into the…
Resolution assessment and performance of several organic modifiers in hybrid micellar liquid chromatography
The performance of four criteria that measure the elementary resolution (modified selectivity, modified RS, peak purity, and orthogonal valley-to-peak ratio) was critically assessed using as global resolution function, the product of elementary measurements. The peak purities and valley-to-peak criteria yielded the best description of the overall separation according to the shape of the resolution surfaces compared to the peak arrangements in the chromatograms, the capability of defining unambiguously the composition regions of complete resolution, and the resolution achieved in the predicted optimums. Peak purities were used to compare the effect of five organic modifiers (1-propanol, 1-bu…
EVALUATION OF THE ELUTION STRENGTH OF THE SURFACTANT AND ORGANIC SOLVENT IN HYBRID MICELLAR MOBILE PHASES
The global ability of a mixed mobile phase (with two or more modifiers) to elute a solute is often measured without distinguishing between the elution strength of each modifier. An algorithm is proposed to evaluate the elution strength of the modifiers in hybrid micellar mobile phases containing a surfactant and an organic solvent. The algorithm is based on a mechanistic retention model that takes into account the competing equilibria of solutes among aqueous-organic phase, micelle, and stationary phase. The change in the elution strength of surfactant and organic solvent with respect to the concentration of both modifiers is also examined. The results are discussed according to the values …
Micellar liquid chromatographic separation of amino acids using pre- and post-column o -phthalaldehyde/ N -acetylcysteine derivatization
Abstract The isocratic analysis of primary proteic amino acids using a C18 column, micellar mobile phases of sodium dodecyl sulphate (SDS) and 1-propanol at varying pH, and pre- and post-column formation of the o-phthalaldehyde (OPA)/N-acetyl- l -cysteine (NAC) isoindoles, is examined. An interpretive optimization strategy was applied to find the best separation conditions. For this purpose, empirical polynomial models were used to describe the elution behavior of the isoindoles and free amino acids, using as separation factors the concentrations of surfactant and modifier (two-factor problem), or these two factors and the pH of the mobile phase (three-factor problem). The separation of the…
SINGLE-PEAK RESOLUTION CRITERIA FOR OPTIMIZATION OF MOBILE PHASE COMPOSITION IN LIQUID CHROMATOGRAPHY
Three criteria that evaluate the single peak resolution (peak purity) in chromatography, the free height fraction, free area fraction, and valley ratio, are examined. The main advantages of these criteria against other criteria based on peak pair separation, are that the measurements are not affected by the identity of neighboring peaks and are normalized, which make them very intuitive. The methodology is illustrated through the isocratic separation of mixtures of several sulphonamides (sulphacetamide, sulphadiazine, sulphadimethoxine, sulphaguanidine, sulphamerazine, sulphamethazine, sulphamethoxazole, sulphamethizole, sulphamonomethoxine, sulphanilamide, sulphapyridine, sulphaquinoxaline…