[Show abstract][Hide abstract] ABSTRACT: The MEEKC separation and on-line preconcentration of nonsteroidal anti- inflammatory drugs (NSAIDs) were investigated. In this work, two microemulsion (ME) systems were employed. Complete separation could be achieved at a pH of 5.5 with octane as the oil phase (ME I). The LODs for the determination of flurbiprofen, fenoprofen, naproxen, ketoprofen, suprofen and indoprofen were 0.45, 0.32, 0.10, 0.48, 0.77 and 0.29 mg/mg, respectively. To enhance the sensitivity, anion selective exhaustive injection-sweeping (ASEI-sweeping) and stacking with reverse migrating pseudostationary phase (SRMP) were compared. For having a simple process without polarity switching and shorter analysis time, a suppressed EOF and di-n-butyl-L-tartrate as the oil phase (ME II) were used for the simultaneous determination of NSAIDs. The sensitivity for ASEI-sweeping was enhanced approximately 280-fold. However, there was much background noise, and some of the analytes were co-eluted. When SRMP was used, all of the analytes could be detected simultaneously, and baseline separation could be achieved. The sensitivities of all of the analytes, except for indoprofen, were enhanced approximately 170-fold compared with the normal MEEKC, and the LODs were 2-45 μg/L. Herein, we propose a simple method for the direct determination of NSAIDs at therapeutic and toxic levels in urine throughout a wide concentration range. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: A monolith molecularly imprinted polymer (MIP) column was prepared from template (-)-norepinephrine, functional monomer (itaconic acid), and a cross-linker (either ethylene glycol dimethacrylate or divinylbenzene) in porogen N,N-dimethylformamide. Understanding the molecular recognition of a template using an MIP seems feasible. However, it is hard to explain the recognition properties of their analogues on an MIP. The separation mechanism was investigated with the addition of charged surfactants, native and derivatised β-cyclodextrin (β-CD), achiral crown ether, etc. to determine the retention behaviour of the template analogues. The addition of organic modifiers and the adjustment of separation conditions were used to manipulate the selectivity. No chiral recognition was observed under most of the test conditions except the experiment with the charged β-CD on the divinylbenzene-MIP column. The different experimental conditions led to differences in the mobilities of the analytes and resulted in remarkable enantiomeric separation of the template. We confirmed the presence of mixed-mode selectivity of the stationary phase based on hydrogen bonding, hydroelectric and hydrophobic interactions, and the electrophoretic mode.
No preview · Article · May 2011 · Journal of Separation Science
[Show abstract][Hide abstract] ABSTRACT: A ZrO(2) nanoparticles (ZrO(2)NPs)-coated column was prepared through a sol-gel process using zirconium(iv) oxychloride, which reacted with silanol groups of the fused-silica capillary. The condensation reaction was carried out at 350 °C for 8 h. Electroosmotic flow (EOF) measurements and scanning electron microscopy (SEM) images were used to characterize the ZrO(2)NPs fabricated on the inner wall of the capillary. Below the pI value (pH 5-6), cathodic EOF elucidated that the phosphate buffer adsorbs tightly on the zirconia surface, resulting in a negatively charged surface. In this work, iron-binding proteins, phosphorylated proteins and glycoproteins were selected as the model compounds. The effects of pH, concentration, buffer type and the organic modifier were studied to optimize the separation efficiency. Iron-binding proteins exhibited a retention time for myoglobin (Mb) < hemoglobin (Hb), which corresponded to the binding constants for ZrO(2)NPs. The α- and β-subunit of Hb could be separated in borate buffer (20 mM, pH 9.0) with MeOH (20%, v/v). Greater affinity of α-casein and bovine serum albumin (BSA) for the stationary phase as the pH decreased was found by comparison with that of conalbumin (ConA) and transferrin (Tf). Interestingly, 14 peaks for glycoisoforms of ovalbumin (OVA) were observed using borate buffer (40 mM, pH 9.0). The established method was also applied to the determination of analytes in the egg whites of chicken and duck eggs.
[Show abstract][Hide abstract] ABSTRACT: A monolithic molecularly imprinted polymer (MIP) column was prepared as the stationary phase for the capillary electrochromatographic (CEC) separation of a group of structurally related compounds including dopamine (DA), (±)-epinephrine (EP), (-)-isoproterenol (ISO), (±)-norepinephrine (NE), (±)-octopamine (OCT), and (±)-synephrine (SYN). Here, (-)-NE was used as the template. Either methacrylic acid (MAA) or itaconic acid (IA) together with a mixture of ethylene glycol dimethacrylate (EDMA) and α,α'-azobis(isobutyronitrile) (AIBN) in N,N-dimethylformamide (DMF) was introduced into a pre-treated, silanised, fused-silica capillary by a thermal non-covalent polymerisation procedure. Optimised conditions for the polymerisation reaction were assessed by the separation efficiency of the template. Both the template/monomer/cross linker molar ratio and the compositions of the functional monomer, cross-linker, and porogen affected polymerisation. The optimum in situ polymerisation reaction was performed at 65 °C for 17 min. By varying CEC parameters like eluent composition and pH, we observed that the addition of SDS to the eluent clearly improved the CEC separations. With a mobile phase of citrate buffer (10 mM, pH 3)/SDS (40 mM)/acetonitrile (2/2/1, v/v/v) solution and an applied voltage of 10 kV, the six related structures of the template and their enantiomeric mixtures were satisfactorily separated at 30 °C.
No preview · Article · Feb 2011 · Journal of Chromatography A