Search results for " SURFACTANT"
showing 10 items of 349 documents
Micellar liquid chromatography for prediction of drug transport.
2000
Abstract The vast majority of well absorbed drugs are transported passively across the cell membranes. Physicochemical descriptors of drug molecules that are believed to influence transcellular transport are routinely used to predict drug absorption by means of complex mathematical models. In this paper, a new in vitro method, based on the retention data in micellar liquid chromatography (MLC), is validated for the prediction of passive drug absorption. The retention of a heterogeneous drugs set in MLC using Brij 35 as surfactant in the mobile phase is compared with the retention data reported in literature obtained in red cell membrane lipid liposomes, human red cell membranes vesicles (ve…
Effect of short-chain alcohols on surfactant-mediated reversed-phase liquid chromatographic systems.
2010
The behaviour of β-blockers in a reversed-phase liquid chromatographic (RPLC) column with mobile phases containing a short-chain alcohol (methanol, ethanol or 1-propanol), with and without the surfactant sodium dodecyl sulphate (SDS), was explored. Two surfactant-mediated RPLC modes were studied, where the mobile phases contained either micelles or only surfactant monomers at high concentration. Acetonitrile was also considered for comparison purposes. A correlation was found between the effects of the organic solvent on micelle formation (monitored by the drop weight procedure) and on the nature of the chromatographic system (as revealed by the retention, elution strength and peak shape of…
Submicellar and micellar reversed-phase liquid chromatographic modes applied to the separation of beta-blockers.
2009
The behaviour of a reversed-phase liquid chromatographic (RPLC) system (i.e. elution order, resolution and analysis time), used in the analysis of β-blockers with acetonitrile-water mobile phases, changes drastically upon addition of an anionic surfactant (sodium dodecyl sulphate, SDS). Surfactant monomers cover the alkyl-bonded phase in different extent depending on the concentration of both modifiers, in the ranges 1 × 10-3-0.15 M SDS and 5-50% acetonitrile. Meanwhile, the surfactant is dissolved in the mobile phase as free monomers, associated in small clusters or forming micelles. Four characteristic RPLC modes are yielded, with transition regions between them: hydro-organic, micellar, …
Performance of different C18 columns in reversed-phase liquid chromatography with hydro-organic and micellar-organic mobile phases
2014
Column selection in reversed-phase liquid chromatography (RPLC) can become a challenge if the target compounds interact with the silica-based packing. One of such interactions is the attraction of cationic solutes to the free silanols in silica-based columns, which is a slow sorption-desorption interaction process that gives rise to tailed and broad peaks. The effect of silanols is minimised by the addition of a competing agent in the mobile phase, such as the anionic surfactant sodium dodecyl sulphate (SDS). In micellar-organic RPLC, the adsorption of an approximately fixed amount of SDS monomers gives rise to a stable modified stationary phase, with properties remarkably different from th…
Prediction of peak shape in hydro-organic and micellar-organic liquid chromatography as a function of mobile phase composition
2007
A simple model is proposed that relates the parameters describing the peak width with the retention time, which can be easily predicted as a function of mobile phase composition. This allows the further prediction of peak shape with global errors below 5%, using a modified Gaussian model with a parabolic variance. The model is useful in the optimisation of chromatographic resolution to assess an eventual overlapping of close peaks. The dependence of peak shape with mobile phase composition was studied for mobile phases containing acetonitrile in the presence and absence of micellised surfactant (micellar-organic and hydro-organic reversed-phase liquid chromatography, RPLC). In micellar RPLC…
Peak half-width plots to study the effect of organic solvents on the peak performance of basic drugs in micellar liquid chromatography.
2009
The addition of the anionic surfactant sodium dodecyl sulphate (SDS) to hydro-organic mixtures of methanol, ethanol, propanol or acetonitrile with water yielded enhanced peak shape (i.e. increased efficiencies and symmetrical peaks) for a group of basic drugs (β-blockers) chromatographed with a Kromasil C18 column. The effect can be explained by the thin layer of surfactant associated to the hydrocarbon chain on the stationary phase in the presence of the organic solvents, which covers the free silanols on the siliceous support avoiding their interaction with the cationic basic drugs. These instead interact with the anionic head of the surfactant increasing their retention and allowing a mo…
Polymerizable and polymeric zwitterionic surfactants: 2. Surface activity and aggregation behaviour in aqueous systems
1991
Abstract The surfactant properties of a series of permanently zwitterionic monomers and polymers were studied with respect to structural variations. A strong influence of the molecular geometry on solubility and aggregation behaviour was observed, in particular for the polymers. Whereas all monomers were water-soluble and true surfactants, the water solubility of the polymers was restricted to selected geometries. Water-soluble polymers showed the properties of classical polysoaps, i.e. low surface activity and solubilization power for hydrophobic solutes. In contrast, water-insoluble polymers formed stable monolayers at the air-water interface and could be deposited onto solid substrates b…
Thermodynamic properties and conductivities of some dodecylsurfactants in water
1988
Densities, heat capacities, enthalpies of dilution, osmotic coefficients and conductivities are reported for dodecylamine hydrochloride, dodecyldimethylammonium and dodecyltrimethylammonium chloride in water over a wide range of concentration. The last two properties were also measured for dodecyltrimethylammonium bromide. From the thermodynamic data partial molar volumes, heat capacities and relative enthalpies and nonideal free energies and entropies were derived as a function of the surfactant concentration. The cmc's and degree of counterion dissociation were also calculated from the transport properties. It is shown that the trends of volumes, enthalpies, free energies and entropies ar…
Interpretive search of optimal isocratic and gradient separations in micellar liquid chromatography in extended organic solvent domains
2020
Abstract Micellar liquid chromatography (MLC) is a reversed-phase mode with mobile phases containing an organic solvent and a micellised surfactant. Most procedures developed in MLC are implemented in the isocratic mode, since the general elution problem in chromatography is less troublesome. However, gradient elution may be still useful in MLC to analyse mixtures of compounds within a wide range of polarities, in shorter times. MLC using gradients is attractive to determine by direct injection moderate to low polar compounds in physiological samples. In these analyses, the use of initial micellar conditions (isocratic or gradient) with a fixed amount of surfactant above the critical micell…
Preparation and characterization of bio-organoclays using nonionic surfactant
2015
The present study was aimed at the preparation and characterization of tailor made hybrid materials, whose peculiar hosting capability could be exploited in biotechnological applications. With this purpose, the modification of K10 montmorillonite by intercalation of Tween 20 surfactant, was accomplished. The influence of two internal parameters, namely pH and surfactant/clay ratio, on the surfactant uptake ability by clay was investigated. The adsorption mechanism was elucidated on the basis of complementary kinetic and equilibrium studies and, then, corroborated by the useful information provided by the FT-IR, TGA and XRD characterization. The gathered results allow to draw the conclusion …