Detection of biogenic amines in C57BL/6 mice brain by capillary electrophoresis electrokinetic supercharging.

Ischemic stroke is caused when blood flow to the brain is stopped and is a major cause of death and long term disability across the globe. Excessive release of neurotransmitters is triggered in the brain by ischemia that mediates neuronal damage and causes ischemic injury. In this study, a simple, sensitive, and on-line preconcentration capillary electrophoresis method based on electrokinetic supercharging (EKS) was developed for the determination of the biogenic amines including dopamine (DA), epinephrine (E), and norepinephrine (NE) in C57BL/6 mice brain. Under the optimized conditions, the analytes were concentrated and detected within 10 min. The detection limits for the analytes ranged from 0.42 to 0.57 ng mL(-1) for a mice brain matrix. With the proposed method, the analyses of three neurochemical amines in C57BL/6 mice brain tissue during cerebral ischemic/reperfusion had been performed successfully.

Determination of enantiomers by FESI-sweeping with an acid-labile sweeper in nonaqueous capillary electrophoresis.

In this work, a facile and highly efficient on-line concentration strategy based on a coupling of field enhanced sample injection (FESI) and sweeping was developed for the determination of trace enantiomers (propranolol, PL) by nonaqueous capillary electrophoresis (NACE). In this FESI-sweeping method, the use of a sample of high acidity and low conductivity (pH* = 2.5, 4.0 µS cm(-1)) allowed for a large amount of analyte injection. Then, the concentration of the analytes was carried out by sweeping based on the interaction of an acid-labile anionic selector, di-n-butyl L-tartrate-boric acid complex acid, and cationic analytes. Simultaneously, the concentrated analytes were released and focused at the boundary of the acid sample solution and separation buffer due to the decomposition of the selector in the acid sample solution. Under the optimum conditions, a 21,000-fold sensitivity enhancement upon normal capillary zone electrophoresis (CZE) was achieved for PL enantiomers. The detection limits of R-propranolol and S-propranolol were 0.26 ng mL(-1) and 0.31 ng mL(-1), respectively. Eventually, the FESI-sweeping method was applied to detect PL enantiomers in plasma, saliva, and urine.

Preparation and characterization of open-tubular capillary column modified with graphene oxide nanosheets for the separation of small organic molecules.

A novel coated capillary was prepared by immobilizing graphene oxide (GO) on the fused-silica capillary (75 µm i.d.) which was derivatized by 3-aminopropyl-trimethoxysilane (APTMS). The bare capillary, APTMS modified capillary (NH2-capillary) and GO coated capillary (GO-capillary) were characterized by streaming potentials (SPs), fluorescence microscope and scanning electron microscope (SEM). The results indicated that the capillary was successfully modified with GO sheets via covalent bonding and electrostatic effect. Compared with bare capillary, greater separation efficiency was achieved by GO-capillary column as a result of the increasing interactions between the small organic molecules and the inner wall of the GO-capillary column originated from the π-π electrostatic stacking. For three consecutive runs, the intra-day relative standard deviations (RSDs) of migration time and peak areas were 0.6-4.3% and 2.8-9.3%, respectively. The inter-day relative standard deviations of migration time and peak areas were 0.2-8.3% and 4.5-9.6%. Additionally, one GO-capillary column could be used for more than 100 runs with no observable changes on the separation efficiency.

A new on-line concentration method of cationic molecules in capillary electrophoresis by a hyphenated micelle to solvent stacking coupling with large amount sample electrokinetic stacking injection.

In this paper, we established a new on-line method using micelle to solvent stacking (MSS) technique combining with large amount sample electrokinetic stacking injection (LASEKSI) for the analysis of cationic molecules. In this MSS-LASEKSI, by modulating the integral EOF across the capillary, a equilibrium state was formed and can be maintained for a long time, leading to the continuous stacking of the analytes on the basis of MSS. Thereby, an extremely large amount sample was permitted to be injected into the capillary and then an improved enrichment fold can be achieved comparing with the each case. The variables affecting the performance of MSS-LASEKSI were investigated and discussed. Under the optimized conditions, 6.3 × 10(3)- and 6.4 × 10(2)-fold enrichment in peak heights upon normal CZE method (injected at 0.5 psi for 3 s) and number of plates of 2.9 × 10(6) and 6.5 × 10(5) were attained for berberine and theophylline, respectively. The developed method described here may provide prospects for exploiting a new concentration technique to achieve higher enrichment factor.

Graphene oxide-Fe3O4 magnetic nanocomposites with peroxidase-like activity for colorimetric detection of glucose.

In this report, graphene oxide-Fe(3)O(4) magnetic nanocomposites were demonstrated to possess intrinsic peroxidase-like activity and enhanced affinity toward H(2)O(2). The nanocomposites retain their magnetic properties and can be effectively separated by a magnet. Significantly, they were proved to be novel peroxidase mimetics which could quickly catalyze oxidation of the peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H(2)O(2), producing a blue-colored solution. Kinetic analysis indicates that the catalytic behavior is in accord with typical Michaelis-Menten kinetics and follows a ping-pong mechanism. On the basis of the high activity, the reaction provides a simple, sensitive and selective method for colorimetric detection of glucose in diabetic urine.

Extremely large volume electrokinetic stacking of cationic molecules in MEKC by EOF modulation with strong acids in sample solutions.

In this report, a novel facile way of online preconcentration of trace levels of analytes in capillary electrophoresis is presented. The proposed strategy is based on the combination of strong acidic phosphate as sample buffers with borate separation buffer containing sodium dodecyl sulfate. When injection voltage is applied, the continuous introduction of low pH sample causes the apparent bulk flow inside the capillary gradually slows down. Finally at a certain point, it reaches the same magnitude as that of the oppositely migrating anionic micelles, thus the frontier of the micelle zone becomes stagnant. This steady state can be maintained for a very long time so that essentially extremely large volume of sample solutions can be injected into the capillary, and the cationic analytes may be efficiently stacked at the neutralized micelle zone. A theoretical model was proposed and preconcentration conditions of two model analytes, matrine and oxymatrine, were optimized with the aid of the model. Under optimized conditions, more than 1000-fold increase in sensitivity was obtained as compared with the normal hydrodynamic injection without sample stacking. The limits of detection for oxymatrine and matrine were 0.81 and 0.18 ng/mL, respectively, using photodiode array UV detection at wavelength 211 nm.