On-line sample concentration of organic anions in capillary zone electrophoresis by micelle to solvent stacking.

Micelle to solvent stacking (MSS) is a new on-line sample concentration technique for charged analytes in capillary zone electrophoresis (CZE). Sample concentration in MSS mainly relies on the reversal in the effective electrophoretic mobility of the analyte at the boundary zone between the sample solution (S) and CZE background solution (BGS) inside the capillary. The basic condition for MSS is that the S is prepared in a matrix that contains an additive (i.e., micelles) which interacts with and has an opposite charge compared to the analytes. In addition, the BGS must contain a sufficient percentage of organic solvent. MSS was first reported for organic cations using anionic dodecyl sulfate micelles as additive in the S and methanol or acetonitrile as organic solvent in the BGS. Here, theoretical and experimental studies on MSS are described for organic anions using cationic cetyltrimethyl ammonium micelles as additive in the S and methanol as organic solvent in the BGS. Up to an order of magnitude improvement in concentration sensitivity was obtained for the test hypolipidaemic drugs using MSS in CZE with UV detection. The optimized method was also evaluated to the analysis of a spiked wastewater sample that was subjected to a simple extraction step.

Guidote AM Jr ，Quirino JP 《-》

Two-step stacking in capillary zone electrophoresis featuring sweeping and micelle to solvent stacking: II. Organic anions.

Two-step stacking of organic anions by sweeping and micelle to solvent stacking (MSS) using cationic cetyltrimethylammonium micelles in co-electroosmotic flow (co-EOF) capillary zone electrophoresis (CZE) is described. The co-EOF condition where the direction of the EOF is the same as the test anions was satisfied by positive dynamic coating of a fused silica capillary with hexadimethrine bromide. The strategy was as follows. After conditioning the capillary with the background solution (BGS), a micellar solution (MS) was injected before the sample solution (S). The BGS, MS and S have similar conductivities. Voltage was applied at negative polarity. The analytes in the micelle-free S zone were swept by micelles from the MS. The swept analytes were brought by the micelles to the MSS boundary where the second stacking step was induced by the presence of organic solvent in the BGS. Finally was the separation of concentrated analytes by CZE. The effect of electrolyte concentration in the S, injection time of the MS and the S and surfactant concentration in the MS were studied. A 20-29, 17-33 and 18-21 times increase in peak height sensitivity was obtained for the test hypolipidaemic drugs (gemfibrozil, fluvastatin and atorvastatin), non-steroidal anti-inflammatory drugs (diflunisal, naproxen, ketoprofen, indoprofen and indomethacin), and herbicides (mecoprop and fenoprop), respectively. The LODs (S/N=3) were from 0.05 to 0.55 μg/mL. The intraday and interday repeatabilities (%RSD, n=12) in terms of retention time, corrected peak area, and peak heights was less than 3.6, 8.9, and 10.8%, respectively. The application of sweeping and MSS in co-EOF CZE together with a simple extraction procedure to a waste water sample spiked with the test herbicides was also demonstrated.

Quirino JP ，Guidote AM Jr 《-》

Micelle to solvent stacking of organic cations in capillary zone electrophoresis with electrospray ionization mass spectrometry.

Quirino JP 《JOURNAL OF CHROMATOGRAPHY A》

Two-step stacking in capillary zone electrophoresis featuring sweeping and micelle to solvent stacking: I. Organic cations.

Two-step stacking of organic cations by sweeping and micelle to solvent stacking (MSS) in capillary zone electrophoresis (CZE) is presented. The simple procedure involves hydrodynamic injection of a micellar sodium dodecyl sulfate solution before the sample that is prepared without the micelles. The micelles sweep and transport the cations to the boundary zone between the sample and CZE buffer. The presence of organic solvent in the CZE buffer induces the second stacking step of MSS. The LODs obtained for the four beta blocker and two tricyclic antidepressant test drugs were 20-50 times better compared to typical injection.

Quirino JP 《-》

On-line sample concentration and determination of cationic alkaloids in human plasma by micelle to solvent stacking in capillary zone electrophoresis.

A sensitive method for the determination of three cationic alkaloids (berberine, palmatine and jatrorrhizine) from human plasma samples was developed by micelle to solvent stacking (MSS) in capillary zone electrophoresis (CZE). In MSS, the sample preconcentration mainly relies on the reversal in the effective electrophoretic mobility of the analytes at the boundary zone between the sample and CZE background solution (BGS). Under the optimized conditions, the sensitivity enhancement factors achieved in terms of corrected peak area were in the range from 47 to 53 for the alkaloids. The limits of detection (LODs) (S/N=3) for berberine, palmatine and jatrorrhizine were 0.01, 0.01 and 0.02μg/mL, respectively. The intraday (n=6) and interday repeatabilities (n=12) expressed as the relative standard deviations (RSDs) were less than 6.9% in terms of peak height and less than 7.3% in terms of corrected peak area, respectively. The recoveries of the method for the three alkaloids were in the range of 95.9-101.5% with peak height as the quantitative signal, and 92.6-103.6% with corrected peak area as the quantitative signal, respectively. The MSS-CZE method proved to be suitable for the analysis of the alkaloids in human plasma samples.

Zhang S ，Ma R ，Yang X ，Wang C ，Wang Z ... -  《-》