Application of micellar electrokinetic capillary chromatography for the determination of benzoic acid and its esters in liquid formula medicines as preservatives

Vertical Liquid Crystal Alignment of Comb-Like Alkyl Hydroxybenzoate-Substituted Polystyrene

We investigated the liquid crystal (LC) alignment behaviors of butyl hydroxybenzoate-substituted polystyrene (PBHB#; # = 20, 40, 60, 80, and 100, where # indicates the molar fraction of butyl hydroxybenzoate in the side chain), methyl hydroxybenzoate-substituted polystyrene (PMHB100), and ethyl hydroxybenzoate-substituted polystyrene (PEHB100). Generally, LC cells made employing polymer films having longer alkyl groups in the side chain show vertical LC alignment. For instance, a LC cell fabricated with the PMHB100 film showed random planar LC alignment, while the LC cells made from the PEHB100 and PBHB100 films exhibited vertical LC alignment. Moreover, LC cells prepared from a polymer film having a higher molar content of butyl hydroxybenzoate in the side chain exhibited vertical LC alignment. The observed vertical LC alignment behaviors are closely related to the surface energy of these polymer films. For instance, vertical LC alignment was observed when the surface energy of the polymer film was less than ~43.86 mJ/m2, which could result from the nonpolar alkyl groups of the alkyl hydroxybenzoate moiety. The LC cell prepared from PBHB100 as the LC alignment layer showed good electro-optical characteristics such as voltage holding ratio, residual DC voltage, and alignment stability at 200 °C.

MEKC as a powerful growing analytical technique

This review summarizes the principle and the developments in MEKC in terms of separation power, sensitivity, and detection approaches more than 25 years after its appearance. Newly used surfactants are mentioned. Classical and new sample concentration techniques in MEKC are described. The different detection approaches in MEKC with advantages, limitations, and future prospects are also discussed. This review highlights the wider application of MEKC in different analytical fields. Various recent selected applications of this technique in different analytical fields are reported.

Simultaneous analysis of antioxidants and preservatives in cosmetics by supercritical fluid extraction combined with liquid chromatography-mass spectrometry

This study evaluated supercritical fluid extraction (SFE) combined with liquid chromatography-mass spectrometry (LC-MS) to determine trace preservatives and antioxidants including methylparaben (MP), ethylparaben (EP), propylparaben (PP), butylparaben (BP), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), alpha-tocopherol (alpha-t) and alpha-tocopherol acetate (alpha-ta) in cosmetic products. A supercritical fluid extraction procedure was used to isolate four paraben preservatives and four antioxidants from the cosmetic matrix before quantitative analysis. The optimum extraction condition was performed with static extraction for 5 min, then dynamic extraction for 20 min by using carbon dioxide supercritical fluid at 14,000 kPa and 65 degrees C. Methanol was used as collection solvent and the sea sand was chosen as a filling material. The analytes were separated on a C18 reversed-phase column using methanol-water as mobile phase and quantified by measuring its mass spectrometry. The linearity range is from 10 to 20,000 ng/g with RSD values below 18%. Detection limits are achieved at the level of 4.7-142 ng/g. It was successfully applied to the determination of paraben preservatives and antioxidants in cosmetics without tedious pretreatment.

Application of a capillary electrophoresis method for simultaneous determination of preservatives in pharmaceutical formulations

Preservatives are used to protect pharmaceutical formulations from microbial attack during the period of administration to the patient. Because of their biological activity, preservatives have to be identified and assayed according to the same rules as apply to active components. A number of methods for separation of preservatives are reported, to account for the heterogeneity of their chemical structures. A capillary electrophoretic method was devised for simple and simultaneous qualification and quantification of the preservatives most often included in pharmaceuticals, such as benzyl alcohol, parabens, phenol, m-cresol, chlorobutanol, thimerosal. After systematic method development, the electrophoretic conditions were defined as: 50 mM borate buffer pH 9.0 containing 20 mM SDS. Separations were performed at a temperature of 20 degrees C and with detection at 214 nm. Preservatives under examination can be analyzed within a 10 min run. The method was successfully validated and applied to the determination of preservatives in a number of pharmaceuticals. Results from the CE method were compared with those from reference methods.

Micellar electrokinetic capillary chromatography determination of +S and -R arotinolol in serum using UV detection and solid phase extraction

A method for the simultaneous determination of +S and -R arotinolol in serum by micellar electrokinetic capillary chromatography is described. Stereoselective resolution of the arotinolol enantiomers was achieved using 5 mM sodium taurocholate in 10 mM sodium dihydrogen phosphate buffer of pH 2.5. A 72-cm uncoated fused-silica capillary at a constant voltage of 15 kV was used for the analysis. The analytes of interest were extracted from serum using solid phase extraction. An octadecyl cartridge gave good recoveries in excess of 87% for both +S and -R arotinolol without any interference. The calibration curves were linear over the range of 50-500 ng ml(-1) with +S propranolol as the internal standard and the coefficient of determination was greater than 0.999 (n = 3). The limit of quantitation was 50 ng ml(-1) for each enantiomer and the detection limit using 1 ml serum and a UV detection set et 220 nm was 25 ng ml(-1) (S/N = 2). Precision and accuracy of the method were in the range 0.8-2.7% and 1.2-6.4%, respectively, for +S arotinolol and 1.1-3.9% and 2.2-6.5%, respectively, for -R arotinolol.

Analysis of agrochemicals by capillary electrophoresis

An increasing amount of articles using capillary electrophoresis as an investigation tool for pesticides and environmental pollutants were found over the last few years in analytical chemistry oriented journals. This review covers a wide literature range of the 1990s and concentrates on the analysis of organic agrochemicals (herbicides, fungicides, insecticides, acaricides, etc.) with capillary electrophoresis (capillary zone electrophoresis, micellar electrokinetic chromatography with CE-UV-visible or laser-induced fluorescence detection) as well as with the on-coming hyphenated techniques like capillary electrophoresis-electrospray ionization mass spectrometry. The principal preconcentration methods that allowed real sample analysis with CE are also briefly discussed. The pesticides, the separation methods, the used electrolytes, the detection types, the detection limits and the preconcentration methods were classified and presented in tabulated form as a rapid information tool.