Separation and selectivity of benzophenones in micellar electrokinetic chromatography using sodium dodecyl sulfate micelles or sodium cholate modified mixed micelles

Physicochemical and chromatographic characteristics of random amphiphilic copolymer aggregation in electrokinetic chromatography

The random amphiphilic polymeric aggregation, self-assembled from poly (methyl methacrylate-co-methacrylic acid) (P(MMA-co-MAA)), was explored as a novel pseudostationary phase (PSP) in electrokinetic chromatography (EKC) in our previous report. This work focused on physicochemical characteristics and PSP performances of the polymeric aggregations. The physicochemical characteristics of polymeric aggregations, including critical aggregation concentration (CAC), zeta potential, hydrodynamic diameter, and micropolarity were determined. Experimental results showed that polymeric aggregations had much lower CAC, which decreased the usage of copolymer in EKC, weakened ionic strength and shortened analysis time. The monomer molar ratio of the copolymer was a key factor for physicochemical characteristics and PSP performances of the polymeric aggregations. With the increase of the hydrophobic monomer molar ratio, CAC, micropolarity and dimension of polymeric aggregation decreased significantly while zeta potentials were similar. Correspondingly, separation window enlarged and methylene selectivity evaluated with six kinds of n-alkylphenone homologous series enhanced. Linear solvation energy relationships (LSER) analysis found that hydrophobic interaction is the most important interaction between analytes and polymeric PSPs. Compared with SDS micelle, polymeric aggregations owned more types of interactions, such as stronger hydrogen bonding and relative larger dipole interaction, which provided a bigger adjustment room to improve PSP selectivity.

Separation of very hydrophobic analytes by micellar electrokinetic chromatography. III. Characterization and optimization of the composition of the separation electrolyte using carbon number equivalents

Four coefficients are suggested to characterize the separation properties of separation electrolytes in MEKC. These coefficients are the electrophoretic mobility of the pseudostationary phase (PSP), the electroosmotic mobility, and two parameters which can be obtained via the Martin equation using the retention data of the members of a suitable homologous series. These four coefficients are used for the characterization of separation electrolytes applicable to the separation of very hydrophobic analytes (log P(OW) = 3-4) with SDS as PSP and to quantitatively describe the influence of the buffer additives ACN and urea for the fine-tuning of retention factors and the additive calcium chloride for the fine-tuning of the width of the migration time window. Together with carbon number equivalents (N*(C)) as analyte descriptors the suggested coefficients provide a tool for the fast optimization of the composition of the separation electrolyte. The proposed method optimization scheme is applied to the separation of ingredients of essential oils. Predicted resolutions are compared to experimental results.

Analyses of benzophenones by capillary electrochromatography using methacrylate ester-based monolithic columns

In this study, eight benzophenones, which are commonly used as UV filters in various cosmetics and plastics, were analyzed by capillary electrochromatography with a methacrylate ester-based monolithic column. The effects of the composition and pH of mobile phase, porogenic solvent ratio, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) content on benzophenone separations were examined. For all benzophenones, separation performances were markedly improved in monolithic columns with larger 1-propanol ratio and higher AMPS content. Furthermore, a twofold increase in AMPS content almost reduced the separation time in half when a monolithic column had an adequately high surface area, i.e. monolithic column was produced in a higher ratio of 1-propanol. As well, the retention behaviors of these analytes in the monolithic column were strongly influenced by the level of acetonitrile in the mobile phase, and the pH of the mobile phase also had an apparent influence on separation resolution.

Separation of synthetic food colourants in the mixed micellar system

The paper presents a rapid method for the determination of commonly used synthetic food dyes by micellar electrokinetic capillary chromatography. Detection and separation conditions allowing complete resolution of 15 synthetic food colourants were investigated. The effect of different surfactants on the analytes mobility in relation to their structure was tested. After optimization procedure a dual micellar system was selected. All food dyes were separated in less then 20 min using a fused silica capillary in the borate/dodecylsulfate/deoxycholate buffer containing acetonitrile as organic modifier. The detection wavelength was set at 210nm. The method was successfully validated by determination of linearity ranges, detection limits, precision and repeatability for all colourants tested. In order to apply the method for pharmaceutical analysis a sample pretreatment procedures were found. Liquid pharmaceuticals were used as it or just after dilution with water. From tablets or capsules the colourants were isolated by adsorption on acidic aluminium oxide. The method was used for identification and if possible for quantification the synthetic food dyes in pharmaceuticals. The analytes are detectable at a concentration level 0.3-0.8 microg ml(-1).

Comparison of microemulsion electrokinetic chromatography and micellar electrokinetic chromatography as methods for the analysis of ten benzophenones

Microemulsion electrokinetic chromatography (MEEKC) and micellar electrokinetic chromatograpy (MEKC) were compared for their abilities to separate and detect ten similar benzophenones, which are commonly used as UV filters in various plastic and cosmetic products. Sodium dodecyl sulfate (SDS) concentration and column temperature rarely affected separation resolution for MEEKC, but separation of benzophenones could be improved by changing the SDS concentration and column temperature for MEKC. Buffer pH and ethanol (organic modifier) were found to markedly influence the separation selectivity for both MEEKC and MEKC systems. In addition, a higher electric voltage improved the separation efficiency without a noticeable reduction in separation resolution for MEEKC, whereas it caused a poor separation resolution for the MEKC system.

Determination of benzophenones in a cosmetic matrix by supercritical fluid extraction and capillary electrophoresis

Benzophenones are common additives in commercial sunscreen products. These UV absorbers were extracted by supercritical fluid extraction (SFE), and then analyzed by capillary zone electrophoresis (CZE) and high-performance liquid chromatography. This study was applied to identify the contents of benzophenones in cosmetic matrix, and simultaneously, to investigate the behavior of migration in CZE. Adding non-ionic surfactant (Tween 20) to optimize the separation in the CZE operation improves resolution. In SFE, we chose carbon dioxide with 2.5% modifier of 10% aqueous phosphoric acid-MeOH (1:1) as the supercritical fluid. Real recoveries of up to 92% with relative standard deviations of less than 4.0% were achieved. These analytical techniques were also applied to assay benzophenones for ten commercial sunscreen cosmetics. We found benzophenone 3 was the most commonly used sunscreen additive in Taiwan.

On-line sample preconcentration in micellar electrokinetic chromatography by sweeping with anionic-zwitterionic mixed micelles

On-line preconcentration by sweeping in micellar electrokinetic chromatography using mixed micelles of sodium dodecyl sulfate (SDS)-SB-12 is presented. Because of their large micelle radius, they permit increased partitioning of hydrophobic analytes into the core. In addition, they also possess lower negative surface charge relative to pure SDS micelles so anionic analytes can be retained better due to decreased electrostatic repulsion. As the efficiency of sweeping is predicated on the magnitude of retention factors, these advantages translated to better focusing. As much as a 370-fold improvement in detector response, in terms of peak height, was obtained for some neutral steroids, while about a 360-fold improvement was obtained for some phenol derivatives, which were previously not amenable to sweeping by pure SDS micelles.