Search results for "Electrokinetic chromatography"
showing 10 items of 47 documents
Fast enantiomeric separation of uniconazole and diniconazole by electrokinetic chromatography using an anionic cyclodextrin: application to the deter…
2000
The enantiomeric resolution of the fungicides uniconazole and diniconazole was performed using electrokinetic chromatography with cyclodextrins as pseudostationary phase (CD-EKC). A systematic evaluation of several chiral selectors was made. The anionic derivative carboxymethylated-gamma-cyclodextrin (CM-gamma-CD) was found to be the most appropriate for the enantioseparation of fungicides among all cyclodextrins tested. The influence of some experimental conditions such as nature and buffer pH, chiral selector concentration, and temperature on the enantiomeric separation of the compounds studied was also investigated. The use of a 50 mM phosphate buffer (pH 6.5) containing 5 mM CM-gamma-CD…
Micellar electrokinetic capillary chromatography for therapeutic drug monitoring of carbamazepine and its main metabolites.
1998
In carbamazepine (CBZ) therapy the concomitant monitoring of concentrations of CBZ and its metabolites is strictly recommended, primarily to avoid toxic side effects. Currently, clinical routine monitoring of CBZ is accomplished by high-performance liquid chromatography or immunological methods. In this study a micellar electrokinetic capillary chromatographic (MECC) method was developed for routine drug monitoring of CBZ and its main metabolites, carbamazepine 10,11-diol and carbamazepine 10,11-epoxide, in human serum or plasma samples. The MECC method enabled baseline separation of all analytes within 2.5 min. The assay revealed sufficient precision and sensitivity and the results of eith…
Retention-structure relationship studies for some steroidal hormones in micellar liquid chromatography
2000
The retention behavior in a C18 column of fourteen steroidal hormones (clostebol acetate, dehydrotestosterone, dydrogesterone, medroxyprogesterone, medroxyprogesterone acetate, methandienone, methyltestosterone, nandrolone, nandrolone decanoate, progesterone, testosterone, testosterone enanthate, testosterone propionate and, stanozolol) with pure micellar mobile phases prepared from sodium dodecyl sulfate (SDS), and hybrid mobile phases comprising SDS-acetonitrile and SDS-pentanol, was correlated with their octanol-water partition coefficients. Similar correlations were found with retention data obtained by other authors in gas chromatography, conventional reversed-phase liquid chromatograp…
Quantitation of hydrophobicity in micellar liquid chromatography
1999
Abstract Micellar liquid chromatography (MLC) is shown to be a promising technique for measuring the hydrophobicity of solutes. The presence of micelles has a profound effect on the chromatographic characteristics of reversed-phase columns. The linear relationships between the logarithm, log k , of the retention factor and such diverse properties as the number of carbon atoms in homologous series, octanol–water partition coefficients and solvatochromic parameters, which are observed in conventional reversed-phase liquid chromatography (RPLC), are not usually valid in MLC. For series of compounds exhibiting a wide range of hydrophobicity, k itself is linearly related to these properties. The…
Influence of the addition of modifiers on solute-micelle interaction in hybrid micellar liquid chromatography
1998
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
2001
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…
Analysis of Urine Samples Containing Cardiovascular Drugs by Micellar Liquid Chromatography with Fluorimetric Detection
1999
A simple direct injection chromatographic procedure with fluorimetric detection is successfully applied to the determination of mixtures of 4 diuretics (amiloride, bendroflumethiazide, piretanide, and triamterene) and 6 beta-blockers (acebutolol, atenolol, labetalol, metoprolol, nadolol, and propranolol), which are usually administered in combinations for the treatment of hypertension, in urine samples. The procedure makes use of C18 columns and micellar mobile phases of sodium dodecyl sulphate (SDS), propanol, and phosphate buffer at pH 3. The adequate resolution of most drugs is obtained with a chemometrics approach where the retention is modeled as a first step using the retention factor…
EVALUATION OF THE ELUTION STRENGTH OF THE SURFACTANT AND ORGANIC SOLVENT IN HYBRID MICELLAR MOBILE PHASES
2001
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 …
Description of the retention behaviour in micellar liquid chromatography as a function of pH, surfactant and modifier concentration
1997
Abstract Micellar liquid chromatography permits the elution of solutes of diverse polarity. One of the most outstanding advantages of the technique is its capability of predicting the retention with high accuracy, as a function of different experimental variables. The separation of a group of compounds is usually optimized by varying the concentrations of surfactant and modifier in the mobile phase. The pH is, however, for many solutes, a variable that should be considered in the description of their elution behaviour. A global model that takes into account, simultaneously, the concentrations of surfactant and modifier, and the pH as chromatographic variables, is proposed for ionizable solu…
Micellar Liquid Chromatography: Fundamentals
2015
The reversed phase liquid chromatography (RPLC) mode with surfactant above the critical micellar concentration (CMC) has been called micellar liquid chromatography (MLC). In pure micellar systems, the retention behavior is explained by considering three phases or environments: surfactant-modified stationary phase, bulk aqueous solvent, and micellar pseudo-phase. Surfactant adsorption on the porous RPLC packing affects chromatographic retention, owing to the change of diverse surface properties of the stationary phase. In pure micellar systems, the retention behavior is explained by considering three phases or environments: surfactant-modified stationary phase, bulk aqueous solvent, and mice…