Search results for " Electrokinetic"
showing 10 items of 70 documents
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…
Analysis of pharmaceutical preparations containing local anesthetics by micellar liquid chromatography and spectrophotometric detection
1999
An HPLC procedure for the determination of six local anesthetics, bupivacaine, lidocaine, mepivacaine, procaine, propanocaine and tetracaine, in pharmaceutical silane ODS-2 C18 analytical column and spectrophotometric detection at 230 nm were used. The chromatographic tographic behaviour of local anesthetics with different micellar eluents of sodium dodecyl sulphate (SDS) is described. Selection of the adequate composition of the micellar mobile phase (SDS and 1-propanol concentrations) for the analysis of pharmaceuticals was studied. Adequate retention was achieved with an eluent containing 0.15 M SDS +10% 1-propanol at pH 3. Application of the proposed method to the analysis of eight phar…
Ionic liquids in separation techniques.
2007
The growing interest in ionic liquids (ILs) has resulted in an exponentially increasing production of analytical applications. The potential of ILs in chemistry is related to their unique properties as non-molecular solvents: a negligible vapor pressure associated to a high thermal stability. ILs found uses in different sub-disciplines of analytical chemistry. After drawing a rapid picture of the physicochemical properties of selected ILs, this review focuses on their use in separation techniques: gas chromatography (GC), liquid chromatography (LC) and electrophoretic methods (CE). In LC and CE, ILs are not used as pure solvents, but rather diluted in aqueous solutions. In this situation IL…
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…
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.…
Resolution assessment and performance of several organic modifiers in hybrid micellar liquid chromatography
2001
The performance of four criteria that measure the elementary resolution (modified selectivity, modified RS, peak purity, and orthogonal valley-to-peak ratio) was critically assessed using as global resolution function, the product of elementary measurements. The peak purities and valley-to-peak criteria yielded the best description of the overall separation according to the shape of the resolution surfaces compared to the peak arrangements in the chromatograms, the capability of defining unambiguously the composition regions of complete resolution, and the resolution achieved in the predicted optimums. Peak purities were used to compare the effect of five organic modifiers (1-propanol, 1-bu…
Determination of water-soluble vitamins in energy and sport drinks by micellar electrokinetic capillary chromatography
2016
Abstract A method for the determination of water-soluble vitamins in several energy and sport drinks by micellar electrokinetic chromatography (MEKC) has been developed in this work. The separation of vitamins was studied in terms of background electrolyte composition (borate content, pH, surfactant type and content) and in other MEKC parameters. A study of the possible compounds found in the vitamin-enriched drinks that could interfere in vitamin determination was also performed, and a modified procedure with enhanced resolution was developed. The proposed method was successfully applied to the analysis of water-soluble vitamins in a variety of energy and sport drinks and also in fruit nec…
Quantitation of hydrophobicity in micellar liquid chromatography
1999
Abstract Micellar liquid chromatography (MLC) is shown to be a promising technique for measuring the hydrophobicity of solutes. The presence of micelles has a profound effect on the chromatographic characteristics of reversed-phase columns. The linear relationships between the logarithm, log k , of the retention factor and such diverse properties as the number of carbon atoms in homologous series, octanol–water partition coefficients and solvatochromic parameters, which are observed in conventional reversed-phase liquid chromatography (RPLC), are not usually valid in MLC. For series of compounds exhibiting a wide range of hydrophobicity, k itself is linearly related to these properties. The…
Determination of procaine and tetracaine in plasma samples by micellar liquid chromatography and direct injection of sample
2001
A liquid chromatographic procedure is proposed for the determination of procaine and tetracaine in plasma samples with direct injection. The method uses a Spherisorb octadecylsilane ODS-2 C18 analytical column and a micellar mobile phase containing 0.15 M sodium dodecyl sulphate, 0.5% triethylamine at pH 2.5 and 10% propanol. The UV detection was carried out at 300 nm. Plasma sample preparation required only adequate dilution with the mobile phase before injection into the chromatographic system. The proposed method allows the determination of procaine and tetracaine in plasma at therapeutic levels.