Time filter

Source Type

Wang L.-J.,Lanzhou University | Wang L.-J.,Hebei University | Liu X.-F.,Hebei University | Lu Q.-N.,Hebei University | And 3 more authors.
Journal of Chromatography A

A chiral recognition mechanism of ion-pair principle has been proposed in this study. It rationalized the enantioseparations of some basic analytes using the complex of di- n-butyl l-tartrate and boric acid as the chiral selector in methanolic background electrolytes (BGEs) by nonaqueous capillary electrophoresis (NACE). An approach of mass spectrometer (MS) directly confirmed that triethylamine promoted the formation of negatively charged di-n-butyl l-tartrate-boric acid complex chiral counter ion with a complex ratio of 2:1. And the negatively charged counter ion was the real chiral selector in the ion-pair principle enantioseparations. It was assumed that triethylamine should play its role by adjusting the apparent acidity (pH*) of the running buffer to a higher value. Consequently, the effects of various basic electrolytes including inorganic and organic ones on the enantioseparations in NACE were investigated. The results showed that most of the basic electrolytes tested were favorable for the enantioseparations of basic analytes using di-n-butyl l-tartrate-boric acid complex as the chiral ion-pair selector. © 2013 Elsevier B.V. Source

Dong Y.-L.,Lanzhou University | Zhang H.-G.,Lanzhou University | Rahman Z.U.,Lanzhou University | Su L.,Lanzhou University | And 4 more authors.

In this report, graphene oxide-Fe 3O 4 magnetic nanocomposites were demonstrated to possess intrinsic peroxidase-like activity and enhanced affinity toward H 2O 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 2O 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. © 2012 The Royal Society of Chemistry. Source

Xu Y.-Y.,Lanzhou University | Niu X.-Y.,Lanzhou University | Dong Y.-L.,Lanzhou University | Zhang H.-G.,Lanzhou University | And 4 more authors.
Journal of Chromatography A

A novel coated capillary was prepared by immobilizing graphene oxide (GO) on the fused-silica capillary (75μm 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. © 2013 Elsevier B.V. Source

Zhu H.-D.,Lanzhou University | Ren C.-L.,Lanzhou University | Hu S.-Q.,Lanzhou University | Zhou X.-M.,Lanzhou University | And 3 more authors.
Journal of Chromatography A

In this paper, the co-solvent of methanol-water was used to facilitate the sodium dodecyl sulfate (SDS) micelles collapse, thereby inducing the on-line sample focusing technique of micelle to solvent stacking (MSS). To demonstrate this stacking method, the mechanism of micelles collapse in co-solvent was discussed. The details of the required conditions were investigated and the optimized conditions were: running buffer, 20mM H3BO3 and 20mM NaH2PO4 solution (pH 4.0); micellar sample matrix, 20mM SDS, 20mM H3BO3 and 20mM NaH2PO4 solution (pH 4.0); co-solvent buffer, 20mM H3BO3 and 20mM NaH2PO4 in methanol/water (90:10, v/v). The validity of the developed method was tested using cationic alkaloid compounds (ephedrine and berberine) as model analytes. Under the optimized conditions, this proposed method afforded limits of detection (LODs) of 0.5 and 1.1ng/mL with 300 and 1036-fold improvements in sensitivity for ephedrine and berberine, respectively, within 15min. © 2010 Elsevier B.V. Source

Li X.,Lanzhou University | Ju Y.,Lanzhou University | Xu Y.,Lanzhou University | Wang W.,Lanzhou University | And 4 more authors.
Analytica Chimica Acta

In this paper, four organic acids constituents of Plateau alfalfa roots have been identified and detected by a novel capillary electrophoresis (CE) strategy which combined chitosan (CS) trapping and cetyltrimethyl ammonium bromide (CTAB) assisted sample stacking. Under the optimized condition, organic acids, i.e., aconitic acid, gallic acid, citric acid and l-malic acid were concentrated and separated within 3min. Validation parameters of this method (such as detection limits, linearity and precision) were also investigated and the limit of detection (LOD) was 2.41-53.9ngmL-1. Linearity was obtained over the magnitude range of 5-4000ngmL-1 approximately for different organic acids and 3×102-1.5×104 folds enrichment was achieved. The method has been applied to the determination of organic acids in roots of normal grown Plateau alfalfa and stressing affected Plateau alfalfa. Satisfactory results and recoveries were obtained in the analysis without costly and complicated sample pretreatment. © 2013 Elsevier B.V. Source

Discover hidden collaborations