Critical micellar concentration determination

Photochemical processes in heterogeneous systems, and across micelle boundaries in particular, clearly has great potential. The photolysis of amphipathic alkylcobaloximes in mixed micelles shows a co-operative effect owing to structure.The photoreduction of anthraquinone in aqueous micellar solution has been compared with that in non-aqueous solution.The dimerization of 3-(n-butyl)cyclopentenone is solvent-dependent and the ratio of isomeric products depends on surfactant concentration. It is suggested that this can be used as a means of critical micellar concentration determination. 

For fluorescence PAH determination in tap water acid-induced cloud point extraction was used. This kind of extraction based on the phase separation into two isotropic liquid phases a concentrated phase containing most of the surfactant (surfactant-rich phase), where the solubilised solutes are exttacted, and an aqueous phase containing a surfactant concenttation closes to the critical micellar concentration. 

The aqueous micellai solutions of some surfactants exhibit the cloud point, or turbidity, phenomenon when the solution is heated or cooled above or below a certain temperature. Then the phase sepai ation into two isotropic liquid phases occurs a concentrated phase containing most of the surfactant and an aqueous phase containing a surfactant concentration close to the critical micellar concentration. The anionic surfactant solutions show this phenomenon in acid media without any temperature modifications. The aim of the present work is to explore the analytical possibilities of acid-induced cloud point extraction in the extraction and preconcentration of polycyclic ai omatic hydrocai bons (PAHs) from water solutions. The combination of extraction, preconcentration and luminescence detection of PAHs in one step under their trace determination in objects mentioned allows to exclude the use of lai ge volumes of expensive, high-purity and toxic organic solvents and replace the known time and solvent consuming procedures by more simple and convenient methods. 

AP has been used to probe micellar media (Saroja et al., 1998). The probe is located at the micellar interface and is well suited to monitoring micellar aggregation. In fact, the sharp change in the fluorescence intensity versus surfactant concentration allows the critical micellar concentration (CMC) to be determined. Excellent agreement with the literature values was found for anionic, cationic and nonionic surfactants. The electroneutrality of 4-AP and its small size are distinct advantages over ionic probes like ANS or TNS. 

Pyrene has been used to investigate the extent of water penetration into micelles and to accurately determine critical micellar concentrations (Kalyanasundaram, 1987). Polarity studies of silica or alumina surfaces have also been reported. In lipid vesicles, measurement of the ratio Ii/Iui provides a simple tool for determination of phase transition temperatures and also the effect of cholesterol addition. 

Newly used chiral surfactants often have a low critical micellar concentration, are highly soluble and can be synthesized both in L- and D-forms. This last feature makes it possible to easily change the migration order of the optical isomers, which is very interesting for the determination of the optical pnrity of drugs, where for quantification purposes it is favorable that the chiral impurity migrates before the main component. 

The volume of the micellar phase is crucial for the determination of partition coefficients. In most cases it is regarded as being proportional to the concentration exceeding the critical micellar concentration of the surfactant ... 

There are several possibilities for the determination of the critical micellar concentration. If the micelles are formed from charged surfactants, a plot of the electrophoretic current at constant high voltage against the surfactant concentration shows an inflection point at the ccmc. It should be noted that the critical micellar concentration changes with temperature, the kind and concentration of counterions, and other buffer ingredients. 

The initial concentration, C0, in square centimeters, was determined directly from the area under the curve of a synthetic boundary trace. Although usual practice is to place solvent in one cell and the solution in the other, the solvent used in this work was a solution of bile salt slightly above its critical micellar concentration, CMC (15), usually 0.5 gram per 100 ml. The solution, which was placed in the other cell, was a more concentrated solution (1.5 to 5.0 grams per 100 ml.). Therefore, since both the solvent and the solution were saturated with monomers, C0 represents an initial concentration difference of bile salts in the micellar phase. The pertinent data for each equilibrium ultracentrifugation experiment are presented in Table I. 

Critical micellar concentrations (CMCs) of sucrose fatty acid esters have been determined by various methods, for mixtures and for pure derivatives (Table III).95,126,390 395 Studies on the lyotropic properties of sucrose... 

In distinction to LPS, the critical micellar concentration of various lipoteichoic acids (LTA) has been measured and determined to be in the range of 2.8 10 M to 5 10 M [98,99], indicating a significantly lower hydrophobicity than for glycerophospholipids which is due to the... 

The bile acids are 24-carbon steroid derivatives. The two primary bile acids, cholic acid and chenodeoxycholic acid, are synthesized in the hepatocytes from cholesterol by hy-droxylation, reduction, and side chain oxidation. They are conjugated by amide linkage to glycine or taurine before they are secreted into the bile (see cholesterol metabolism. Chapter 19). The mechanism of secretion of bile acids across the canalicular membrane is poorly understood. Bile acids are present as anions at the pH of the bile, and above a certain concentration (critical micellar concentration) they form polyanionic molecular aggregates, or micelles (Chapter 11). The critical micellar concentration for each bile acid and the size of the aggregates are affected by the concentration of Na+ and other electrolytes and of cholesterol and lecithin. Thus, bile consists of mixed micelles of conjugated bile acids, cholesterol, and lecithin. While the excretion of osmotically active bile acids is a primary determinant of water and solute transport across the canalicular membrane, in the canaliculi they contribute relatively little to osmotic activity because their anions aggregate to form micelles. 

Gao, Z., Wasylishen, R.E., and Kwak, J.C.T., An NMR paramagnetic relaxation method to determine distribution coefficients of solubilization in micellar systems, J. Phys. Chem., 93, 2190, 1989. Treiner, C., The partitioning of neutral solutes between micelles and water as deduced from critical micelle concentration determinations, in Solubilization in Surfactant Aggregates, Christian, S.D. and Scamehorn, J.R, Eds., Marcel Dekker, New York, 1995, chap. 12. 

The surface tension measurements demonstrated that all compounds with a lipophilic alkyl chain of more than 12 carbon atoms display surfactant behavior and self-aggregate into micelles above the critical micellar concentration (cmc). The cmc values decrease from 1 x 10 to 2.5 x 10 while the hydrocarbon chain length increases and the usual linear variation of log cmc versus number of carbon atoms was observed. Moreover the variation of the counter-anion X shows the cmc values in the HEA-Ci series decrease from Cl>Br>BF4>Ms>I and finally the determination of the cmc value of the surfactant affords the possibility to optimize the efficiency of the colloidal catalyst in biphasic liquid-liquid systems (vide infra). The... 

These micellar systems were characterised before polymerisation by their Critical Micellar Concentration (CMC) and their aggregation number Na- This was done using classic methods like conductivity and spectrofluorometry. Such determinations are essential. CMC measurements serve as a guide in choosing and interpreting polymerisation conditions. Measurements of Na help us to understand polymerisation mechanisms. Values are compared with degrees of polymerisation of amphiphile polymers obtained from these surfactants. 

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