Search results for "Surfactant"
showing 10 items of 397 documents
Quantitative Retention−Structure and Retention−Activity Relationship Studies of Local Anesthetics by Micellar Liquid Chromatography
2011
The retention of compounds in micellar liquid chromatography (MLC) is governed by hydrophobic and electrostatic forces. For ionic compounds, both interactions should be considered. The present report offers a novel retention model that includes the hydrophobicity of compounds and the molar fraction of the charged form of compounds and compares it with other previously reported models. High correlations between the logarithm of capacity factors and these structural parameters were obtained for local anesthetics with different degrees of ionization using a nonionic surfactant solution as mobile phase. Modeling the retention of compounds as a function of physicochemical parameters and experime…
Quantitative retention—structure and retention—activity relationship studies of ionic and non-ionic catecholamines by micellar liquid chromatography
1997
When ionic surfactants are used as mobile phases in micellar liquid chromatography, MLC, the retention of compounds is governed by hydrophobic and electrostatic forces. In the absence of electrostatic effects, the hydrophobicity of a compound is the predominant factor affecting its retention and its interaction with micelles. Because both interactions should be considered for ionic compounds, a novel retention model is proposed which includes the hydrophobicity of a compound and the molar fraction of its charged form. High correlations between the logarithm of the capacity factors and structural parameters were obtained for ionic compounds with different degrees of ionization. The effect of…
Effects of polysorbate 80 on amiodarone intestinal absorption in the rat
1995
Abstract Amiodarone is a widely used anti-arrhythmic agent which shows physico-chemical properties that are highly suitable for diffusion across lipophilic absorbing membranes, however,.its low aqueous solubility could represent the rate-limiting step for absorption, making it erratic and variable. In a previous paper, the influence of an anionic surfactant (sodium lauryl sulphate) at variable supramicellar concentrations was studied. The absorption rate constants of amiodarone decreased as the surfactant concentration increased, and absorption was unusually fast at lower surfactant concentrations. The previously proposed equations for interpreting the relationships between the amiodarone a…
Analysis of tricyclic antidepressants in pharmaceuticals by microemulsion liquid chromatography
2021
Abstract Basic compounds yield long retention times and broad and asymmetric peaks in reversed-phase liquid chromatography, due to interaction with residual silanols in the columns. The addition of the surfactant sodium dodecyl sulphate in the so called micellar liquid chromatography enhances the efficiency, but long retention is achieved, due to electrostatic interaction between the cationic species of basic compounds and the anionic sulphate group of the surfactant. This forces the addition of a strong organic solvent to get appropriate times. An alternative is the use of a microemulsion (ME), formed by mixing surfactant, oil and an alcohol as co-surfactant. Association of hydrophobic com…
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…
Clay-biosurfactant materials as functional drug delivery systems: Slowing down effect in the in vitro release of cinnamic acid
2017
Abstract The main objectives of the present paper were the preparation and characterization of new surfactant-modified clays and the evaluation of their potential applicability as drug delivery systems for the oral administration of the cinnamic acid (CA) drug. The organoclays (OC) were prepared by loading different amounts of the biocompatible nonionic polyoxyethylene sorbitan monolaurate surfactant (Tween20) onto K10 montmorillonite (Mt) clay and characterized through the construction of the adsorption isotherms by means of the spectrophotometric method. The performance of the prepared material was verified by gathering the adsorption isotherms of the cinnamic acid onto the Mt/Tween20 org…
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…
Improving the solid-phase extraction of “quat” pesticides from water samples
1998
A novel strategy, based on the addition of a cationic surfactant, for preventing the interferences associated with a diminution in the efficacy of solid-phase extraction (SPE) with silica cartridges of diquat, paraquat and difenzoquat in water is developed. Conditions for extraction are optimised with respect to pH, cationic surfactant and its concentration. Humic acids, anionic surfactants, inorganic salts and other organic contaminants like pesticides, phenols, polycyclic aromatic hydrocarbons and polychlorinated biphenyls produce the studied interferences. The best performance is shown in the improvement of the "quats" recovery from waters with high levels of humic acids and anionic surf…