Search results for "Micellar"
showing 10 items of 185 documents
Evaluation of enantioselective binding of propanocaine to human serum albumin by ultrafiltration and electrokinetic chromatography under intermediate…
2011
Abstract Stereoselectivity in protein binding can have a significant effect on the pharmacokinetic and pharmacodynamic properties of chiral drugs. In this paper, the enantioselective binding of propanocaine (PRO) enantiomers to human serum albumin (HSA), the most relevant plasmatic protein in view of stereoselectivity, has been evaluated by incubation and ultrafiltration of racemic PRO–HSA mixtures and chiral analysis of the bound and unbound fractions by electrokinetic chromatography using HSA as chiral selector. Experimental conditions for the separation of PRO enantiomers using HSA as chiral selector and electrokinetic chromatography have been optimised. Affinity constants and protein bi…
Surfactant Association: Recent Theoretical and Experimental Developments
1991
A theoretical model describing the association of ionic surfactants into rod-shaped micelles is combined with an approximate formula for the viscosity increase induced by rod-shaped aggregates. It is shown that most of the thermodynamic parameters of the association model can be obtained from viscosity measurements. The approach is applied to micellar solutions of hexadecylpyridinium salts. The pronounced effect of counter-ion concentration on the growth of rod-shaped micelles can be attributed to a slightly higher degree of counter-ion association in the cylindrical part than in the end portions. An attempt is made to explain the finding that the degree of counter-ion association is virtua…
Enthalpy of Solution of Nonionic Solutes in Organized Systems
1989
The standard enthalpies of solution of alcohols in micellar solutions of dodecyltrimethylammonium bromide were obtained by direct measurements and by enthalpies of mixing. The observed trends were analyzed with a previously reported model. From the resulting equations, the distribution constant, standard enthalpy of transfer from aqueous to the micellar phase and the standard enthalpy of solution in micellar phase can be calculated at the same time using a linear least-squares analysis. The model seems to hold well also in the case of short chain surfactants and microheterogeneities in spite of the fact that the micellization equilibrium is treated as a pseudo-phase transition.
α, ω-Dipolar amphiphiles: Influence of rigid and flexible units on aggregation behavior
1993
Mono- and α,ω-dipolar amphiphiles with hydrophilic pyridinium head groups, and flexible and rigid hydrophobic parts have been synthesized. Surface tension and conductivity measurements proved that micellar aggregates for amphiphiles 1–4 are formed. The incorporation of rigid units leads to a decrease in the critical micellar concentration (CMC): the rigid monopolar amphiphile 2 aggregates at lower concentration than the flexible monopolar amphiphile 1. A similar decrease was observed when chain ends were connected: the flexible α,ω-dipolar amphiphile 3 has a lower CMC than the flexible monopolar amphiphile 1. The more flexible amphiphiles 1–3 allow the formation of micelles of different sha…
Micellar electrokinetic chromatography with bile salts for predicting ecotoxicity of aromatic compounds.
2004
The retention factors of several aromatic compounds were obtained by micellar electrokinetic chromatography (MEKC) using cholate, taurocholate, deoxycholate and deoxytaurocholate as micellar systems. The possibility of using these retention factors to describe and predict several ecotoxicological activities of different aromatic compounds was evaluated. Adequate correlations retention–ecotoxicity (log LC50 in fish and daphnia, log EC50 in green algae and daphnia, chronic values in fish and green algae, bioconcentration factor, and soil sorption coefficient) were obtained for the micellar systems studied. The predictive ability of the models obtained for these micellar systems was compared. …
Detection of banned drugs in sport by micellar liquid chromatography
1992
Abstract A rapid method for the determination of banned drugs in sport (including stimulants, anabolic steroids and diuretics) based on micellar liquid chromatography is proposed. The mobile phase is an aqueous solution of a surfactant (sodium dodecyl sulphate in this instance) and the stationary phase is octadecylsilica. The retention parameters of the drugs were established and the effect of a mobile phase organic modifier on the chromatographic behaviour of the compounds was studied. Improvements in efficiency were achieved by control of the temperature of the mobile phase. This method allows the direct injection of urine samples for the determination of drugs excreted free in urine: ami…
Determination of phenolic antioxidants in vegetal and animal fats without previous extraction by dilution with n-propanol and micellar liquid chromat…
1999
Abstract A simple and rapid HPLC method for the determination of phenolic antioxidants (propyl and octyl gallates, tert -butylhydroquinone and 3- tert -butyl-4-hydroxyanisole) in sunflower, corn and olive oils, margarine, lard and butter oil is described. The samples are diluted with n -propanol, filtered and injected; solutions containing 30% (w/w) sample can be injected. The analytes are separated with a C18 column and a micellar mobile phase containing 0.1 M SDS, 2.5% n -propanol and 10 mM phosphate of pH 3, and detected at 290 nm. Calibration curves are linear ( r > 0.9999) and the limits of detection range from 0.2 to 1.3 ng, which correspond to antioxidant concentrations well below t…
Determination of thyreostatics in animal feed by micellar electrokinetic chromatography
1999
The determination of the thyreostatics 2-thiouracil, its derivatives (4-methyl-2-thiouracil, 4-propyl-2-thiouracil and 4-phenyl-2-thiouracil) and methimazole in manufactured dried animal feed by micellar electrokinetic chromatography (MEKC) is described. A 99 +/- 5% extraction yield at the 20 micrograms g-1 level (n = 8) was achieved by shaking the milled fodder with methanol-1 M NaOH (80 + 20). Aliquots of the supernatant were injected in a 75 microns x 33.5 cm uncoated silica capillary using pressure; separation was performed at 23 degrees C with 15 kV (positive polarity) in a background electrolyte (BGE) containing 40 mM sodium dihydrogenphosphate, 50 mM sodium dodecyl sulfate and 15 mM …
Determination of Parabens in Cosmetics without Previous Extraction by Micellar Liquid Chromatography
1999
A simple and rapid micellar liquid chromatography method for the determination of p-hydroxybenzoic acid esters (methyl-, ethyl-, n-propyl-, and n-butylparaben) in cosmetics (bath foam, milk lotion, hand cream, cream base, and shampoo) is described. The samples are solved with n-propanol, further diluted with more n-propanol or with an aqueous sodium dodecyl sulphate (SDS) micellar solution, and injected. Separations are performed with a micellar mobile phase containing 0.1M SDS, 2.5% n-propanol, 10mM phosphate (pH 3), and with an octadecyl silica column (C 18 ). Calibrations are linear (correlation coefficient r > 0.999) and the limits of detection range from 0.03 to 0.3 ng paraben. The det…
Analysis of post-harvest fungicides by micellar electrokinetic chromatography.
2001
A method based on solid-phase extraction (SPE) and micellar electrokinetic chromatography (MEKC) was developed for the simultaneous determination of carbendazim, imazalil, methylthiophanate, O-phenylphenol, prochloraz, procimidone, thiabendazole and triadimefon residues in grape, lettuce, orange and tomato. Selectivity and resolution were studied changing the pH and the concentration of the buffer, the type and concentration of surfactant and the methanol content in the mobile phase. A buffer consisting of 4 mM borate with 75 mM sodium cholate (pH 9.2) gave the best results. The recoveries of the fungicides in spiked fruit and vegetable samples ranged from 30 to 105%, and the limits of dete…