A direct on-line complexion combined with micelle to solvent stacking method was proposed for simultaneous determination of metal ions by capillary electrophoresis coupled diode array detector. During the experiment, a plug of complexing agent was first injected to the inlet of capillary, followed by introducing the micelle-bound metal ions. Then the metal ions produced a micelle-to-solvent stacking effect and interacted with the complexing agent under a positive voltage. Continued application of voltage, the analytes were effectively focused and separated in the capillary zone electrophoresis . Repeatability was ranged from 1.89% to 1.94% for the migration time. The detection limits were 2.66–27.9 ng mL -1 for Ni 2+ , Co 2+ , Cu 2+ , Hg 2+ and Cd 2+ . Furthermore, the developed method showed a great potential for the determination of metal ions in the crayfish, beebread and Dendrobium officinale samples.
Ya-Ling Yu,Si-Chen Zhu,Min-Zhen Shi,Fang-Ming Liu,Jun Cao
An effective and sensitive two-step stacking of arsenic species by electrokinetic injection and micelle-to-solvent stacking (MSS) using zwitterionic surfactant 3-(N,N-dimethylpalmitylammonio) propane sulfonate was successfully developed in a co-electro-osmotic flow (co-EOF) capillary zone electrophoresis (CZE). The fused silica capillaries were coated with 1% hexadimethrine bromide solution to satisfy the condition of the same EOF direction between the test anions and capillary. The background solution was 100 mM borax buffer (pH 9.2). The proposed method was performed by a CZE system equipped with a diode array detector, and the detection wavelength was monitored at 192 nm. The separation voltage was −20 kV. The group of micelles and target analytes was stacked by field-enhanced sample injection at −10 kV for 180 s. The second stacking step used 60% MeOH to serve as an organic solvent where the analytes were brought by the micelles to the MSS boundary. The enrichment factors of As(Ⅴ), As(Ⅲ), disodium methyl arsonate hexahydrate (MMA), and dimethylarsinic acid (DMA) were 1230, 840, 3820, and 1450, respectively, compared to typical injections in CZE. The limits of detection (S/N = 3) ranged from 0.382 to 0.911 ng mL −1 . The intracapillary repeatabilities (%RSD, n = 3) were 0.5–1.0% for migration time and 0.3–0.7% for peak areas. The technology of two-step stacking by MSS in co-EOF CZE together with a simple extraction procedure for As(Ⅴ), As(Ⅲ), MMA and DMA were demonstrated in kelp and rice samples.
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