M.L. Marina

Correlation between the logarithm of capacity factors for aromatic compounds in micellar electrokinetic chromatography and their octanol-water partition coefficients

The correlation between the logarithm of the capacity factors (log k′) and the logarithm of the octanol-water partition coefficients (log Pow) for a group of 20 organic compounds (ten benzene derivatives and ten polycyclic aromatic hydrocarbons) was studied in micellar electrokinetic chromatography. Sodium dodecyl sulphate micelles in different aqueous and hydro-organic (n-propanol and n-butanol) buffers were used as electrolyte solutions. A linear relationship between log k′ and log Pow was found. This correlation improved when the percentage of alcohol in the buffer system was increased and when the polarity of the alcohol was decreased.

Separation of chiral polychlorinated biphenyls by micellar electrokinetic chromatography using β- and γ-cyclodextrin mixtures in the separation buffer

Chiral polychlorinated biphenyls (PCBs) 45, 84, 88, 91, 95, 132, 136, 139, 149, 171, 183 and 196 were separated each in its two enantiomers by cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC). Mixtures of β- and γ-cyclodextrins were used as chiral modifiers in a 2-(N-cyclohexylamino)ethanesulphonic acid (CHES) buffer containing urea and sodium dodecyl sulphate (SDS) micelles. Separations of multicomponent mixtures of PCBs into their enantiomers were also performed. A mixture of PCBs 45, 88, 91, 95, 136, 139, 149 and 196 was separated into all sixteen enantiomers in an analysis time of approx. 35 min.

Determination of solute-micelle association constants for a group of benzene derivatives and polycyclic aromatic hydrocarbons with sodium dodecyl sulphate by micellar electrokinetic chromatography

Abstract Micellar electrokinetic chromatography was applied to determine solute-micelle association constants for a group of benzene derivatives and polycyclic aromatic hydrocarbons using sodium dodecyl sulphate as surfactant. Among the different buffers studied, only those of pH⩾9 [2-(N-cyclohexylamino)ethanesulphonic acid and ammonium acetate] gave an electroosmotic flow high enough to allow the elution of all compounds studied. Determination of association constants was achieved under different experimental conditions and the resulting errors were evaluated. The effect of the nature and concentration of the buffer and the alcohol (n-propanol and n-butanol) on the values obtained by this technique for solute-micelle association constants was studied. It was observed that these factors do not affect the association constants under the experimental conditions used. The values of the solute-micelle association constants and the errors in their determination were also compared with those obtained previously by micellar liquid chromatography.

Rapid separation of soybean globulins by reversed-phase high-performance liquid chromatography

A rapid separation of the main soybean proteins (7S and 11S globulins) was carried out by reversed-phase high-performance liquid chromatography. For this purpose, a linear binary gradient acetonitrile--water--0.1% trifluoroacetic acid, at a flow-rate of 1 ml/min and 50 degrees C temperature was designed. Under the experimental conditions of this work, it was possible to separate five peaks corresponding to the globulins from a soybean protein isolate in 9 min. The characterization of soybean proteins was accomplished by analyzing the 7S and 11S purified fractions obtained from a soybean protein isolate. The method was applied to the separation of soybean proteins from commercial foodstuffs: soybean flour, textured soybean and soybean milks.

Enantiomeric separation of bupropion enantiomers by electrokinetic chromatography: quantitative analysis in pharmaceutical formulations.

The first CE method enabling the quantitation of the two enantiomers of bupropion was developed in this work. Electrokinetic chromatography (EKC) mode using cyclodextrins as chiral selectors was employed. A study on the enantiomeric separation ability of different neutral and anionic CDs was carried out. Sulfated-beta-CD was shown to provide the highest values for the enantiomeric resolution. The influence of some experimental conditions, such as pH, chiral selector concentration, temperature, and separation voltage on the enantiomeric separation of bupropion was also studied. The use of 10 mM sulfated-beta-CD in 50 mM borate buffer (pH 9.0) with an applied voltage of 30 kV and a temperature of 30 degrees C enabled the separation of the enantiomers of bupropion with high resolution (Rs > 7) and short analysis time (approximately 3.5 min). Finally, the method was successfully applied to the quantitation of bupropion in two pharmaceutical formulations.

Retention modeling in micellar liquid chromatography

The aim of this review is to present the most relevant work on retention modeling in micellar liquid chromatography. First, physico-chemical models explaining the variation of capacity factors with one or more experimental variables (such as micellar concentration, organic modifier concentration, and pH) will be shown. Secondly, studies carried out to model the solute retention in micellar liquid chromatography by means of empirical equations will be presented, and finally new trends in this area will be introduced.

Chiral separation of polychlorinated biphenyls by micellar electrokinetic chromatography with γ-cyclodextrin as modifier in the separation buffer

SummaryCyclodextrin-modified micellar electrokinetic chromatography has enabled the chiral separation of polychlorinated biphenyls (PCBs). Twelve PCBs (45, 84, 88, 91, 95, 132, 136, 139, 149, 171, 183 and 196) were individually separated into their two enantiomers by using γ-cyclodextrin as modifier in a separation buffer containing 2-(N-cyclohexylamino)ethanesulphonic acid (CHES) and sodium dodecyl sulphate (SDS) micelles. Multicomponent separations were also performed. The separation of the eighteen enantiomers of a mixture of nine chiral PCBs has been performed in a short analysis time (ca. 35 min).

Ultrarapid detection of bovine whey proteins in powdered soybean milk by perfusion reversed-phase high-performance liquid chromatography

A perfusion reversed-phase high-performance liquid chromatographic method has been developed to simultaneously separate soybean and bovine whey proteins (alpha-lactalbumin and beta-lactoglobulins (A + B)) in a very short analysis time (approximately 5 min). The method consisted of a linear binary gradient water-acetonitrile-0.10% trifluoroacetic acid at a flow-rate of 3 ml/min, with the column thermostated at 60 degrees C, and ultraviolet detection at 254 nm. This method enables the rapid detection of adulterations of powdered soybean milks by addition of bovine whey proteins. When bovine whey proteins were too low to be detected by direct injection of the sample, a previous acidic precipitation step was required in order to concentrate these proteins. Quantitatve analysis of bovine whey proteins was also successfully performed. In fact, it was possible to detect about 1% and 1.3% of alpha-lactalbumin and beta-lactoglobulins, respectively, in a commercial powdered soybean milk in which these proteins were included in its formulation. Results were compared with those obtained by conventional reversed-phase high-performance liquid chromatography.

Evaluation of distribution coefficients in micellar liquid chromatography

The possibilities of micellar liquid chromatography for evaluating distribution coefficients are discussed. Determination of solute-micelle association constants and distribution coefficients of solutes between stationary-aqueous, stationary-micellar and aqueous-micellar phases is described. Application of the calculation of distribution coefficients to the study of the retention mechanism of solutes in the chromatographic system and prediction of separation selectivity is also presented.

Capillary Electrophoresis: A Good Alternative for the Separation of Chiral Compounds of Environmental Interest

Capillary electrophoresis potential for the separation of the enantiomers of chiral compounds of environmental interest is described. Applicability of capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) to achieve these separations is discussed.