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

Abstract

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.

Two‐step stacking by sweeping and micelle to solvent stacking using a long‐chain cationic ionic liquid surfactant

“…Then, for further development, two-step online preconcentration methods were established. Coupling of sweeping and MSS for organic cations and anions was reported [22,23]. Compared with MSS, the difference is that there is no micelle in the sample solution.…”

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

“…To overcome this problem, some on-line preconcentration strategies have been developed to increase the sensitivity of CE, such as field amplification [20], dynamic pH junction [21], transient isotachophoresis (tITP) [22], isotachophoresis by acetonitrile stacking [23,24] and sweeping [25] or sweeping in couple with other techniques [26][27][28][29]. The more recent CE on-line preconcentration techniques include electrokinetic supercharging [30], analyte focusing by micelle collapse (AFMC) [31][32][33] and micelle to solvent stacking (MSS) [34][35][36][37][38][39][40][41][42]. The main advantage of the on-line preconcentration strategies is the ease of experimental manipulations without the need of modifications of the commercial CE instrumentation.…”

High‐sensitivity capillary and microchip electrophoresis using electrokinetic supercharging

“…This boundary could be created by change in conductivity (as in field-amplified, and isotachophoretic stacking), change in pH (as in dynamic pH-junction), and inclusion of a pseudostationary phase (as in sweeping, analyte focusing by micelle collapse, and micelle to solvent stacking) [6][7][8][9][10][11][12][13][14][15]. In these stacking techniques, sample is usually introduced into the electrophoretic system by pressurized injection.…”