Search results for "Micellar"

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: suitable technique for screening analysis.

2002

The screening capability of micellar liquid chromatography (MLC) is discussed using the reported chromatographic data of several sets of compounds (amino acids, beta-blockers, diuretics, phenethylamines, phenols, polynuclear aromatic hydrocarbons, steroids and sulfonamides) and new results (sulfonamides and steroids). The chromatographic data are treated with an interpretive optimisation resolution procedure to obtain the best separation conditions. Usually, the pH and the concentration of surfactant (sodium dodecyl sulfate, SDS, or cetyltrimethylammonium bromide) for the optimal mobile phase were 2.5-3 and0.12 M, respectively. The nature and concentration of organic solvent depended on the…

Volumes and compressibilities of pentanol in aqueous alkyltrimethylammonium bromide solutions at different temperatures

1990

Speed of sound and density properties of ternary water-tetradecyltrimethylammonium bromide-pentanol system at 15, 25 and 35°C and of water-hexadecyltrimethylammonium bromide-pentanol system at 25, 35 and 45°C were measured at fixed alcohol concentration as a function of surfactant concentration. The apparent molar volumes Vϕ,R and isentropic compressibilities Kϕ,RS of pentanol in micellar solutions as a function of the surfactant concentration show irregular behavior which depends on the alkyl chain length of the surfactant and tends to disappear with increasing temperature. These anomalies are ascribed to micellar transitions. For both surfactants at high concentrations, Vϕ,R decrease and …

Modelling of retention behaviour of solutes in micellar liquid chromatography

1997

In micellar liquid chromatography (MLC), the resolution for a given multi-component mixture can be optimized by changing several variables, such as the concentrations of surfactant and organic modifier, the pH and temperature. However, this advantage can only be fully exploited with the development of mathematical models that describe the retention and the separation mechanisms. Several reports have appeared recently on the possibilities of accurately predicting the solute retention in MLC. Although the retention and selectivity may strongly change with varying concentrations of surfactant, organic modifier and/or pH, the observed changes are very regular, and are well described by simple m…

Reliability of the retention factor estimations in liquid chromatography.

2004

The retention factor is one of the most universally used parameters in chromatography. However, large differences in the experimental retention factor values are observed when the same compound is injected in a given stationary/mobile phase system under intermediate precision conditions. Conventional protocols for estimating retention factors have problems that mainly arise from difficulties in the hold-up time measurements and the omission of the existence of extra-column times by practicing chromatographers. In the present paper, three different approaches for estimating retention factors are tested: (i) classical retention factor estimations based on the gross hold-up time, (ii) based on…

Micellar Liquid Chromatography: Method Development and Applications

2015

Capillary electrophoresis for analyzing pesticides in fruits and vegetables using solid-phase extraction and stir-bar sorptive extraction.

2005

Two procedures based on solid-phase extraction (SPE) and stir-bar sorptive extraction (SBSE) in combination with micellar electrokinetic chromatography (MEKC)--diode array detection (DAD) were compared for the simultaneous extraction of acrinathrin, bitertanol, cyproconazole, fludioxonil, flutriafol, myclobutanil, pyriproxyfen, and tebuconazole in lettuce, tomato, grape, and strawberry. Selectivity and resolution of the MEKC procedure were studied changing the pH and the molarity of the buffer, the type and the concentration of surfactant, and the methanol content in the mobile phase. A buffer consisting of 6 mM sodium tetraborate decahydrate with 75 mM of cholic acid sodium solution (pH 9.…

Quantitative retention–structure and retention–activity relationships of barbiturates by micellar liquid chromatography

1998

Abstract Studies on the structural requirements of chromatographic surfaces to emulate in vitro the partitioning process in biomembranes are of great interest. The use of micellar mobile phases in RPLC modifies the hydrophobicity of the stationary phase and provides hydrophobic and electrostatic sites of interaction as a consequence of the adsorption of surfactant monomers to the chromatographic surface. Modified stationary phases in MLC could be structurally similar to biomembranes, but thorough studies are necessary to confirm this. In this paper we focus our attention on barbiturates. The influence of the nature and concentration of the surfactant (Brij 35, SDS and CTAB) and the mobile p…

Development of predictive retention-activity relationship models of non-steroidal anti-inflammatory drugs by micellar liquid chromatography: comparis…

2000

The predictive and interpretative capability of quantitative chromatographic retention-biological activity models is supported by the fact that under adequate experimental conditions the solute partitioning into chromatographic system can emulate the solute partitioning into lipid bilayers of biological membranes, which is the basis for drug and metabolite uptake, passive transport across membranes and bioaccumulation. The use of micellar solutions of Brij35 as mobile phases in reversed-phase liquid chromatography has proven to be valid to predict some biological activities of different kinds of drugs. In this study, quantitative retention-activity relationship (QRAR) models to describe som…