Su Hsiu-Li, Feng Lan-Ing, Jen Hsiu-Ping, Hsieh You-Zung
Department of Applied Chemistry, National Chiao Tung University, Hsinchu, Taiwan, ROC.
Electrophoresis. 2008 Nov;29(20):4270-6. doi: 10.1002/elps.200800167.
We have employed a high-sensitivity on-line preconcentration method, cation-selective exhaustive injection (CSEI) and sweeping MEKC, for the analysis of cocaine, benzoylecgonine, norcocaine, and cocaethylene. We monitored the effects of several of the CSEI-sweeping-MEKC parameters - including the pH, the concentrations of SDS and organic modifier, the injection length of the high-conductivity buffer, and the injection time of the sample - to optimize the separation process. The optimal BGE was 100 mM phosphoric acid (pH 1.8) containing 75 mM SDS with 10% 2-propanol and 10% tetrahydrofuran as the organic modifier. In addition, electrokinetic injection of the sample at 15 kV for 900 s provided both high separation efficiency and enhanced sweeping sensitivity. The sensitivity enhancements for cocaine, norcocaine, and cocaethylene ranged from 2.06 x 10(4) to 3.96 x 10(4); for benzoylecgonine it was 1.75 x 10(3); the coefficients of determination exceeded 0.9958. The LODs, based on an S/N ratio of 3:1, of sweeping-MEKC ranged from 33.5 to 52.8 ng/mL; in contrast, when using CSEI-sweeping-MEKC the sensitivity increased to range from 29.7 to 236 pg/mL. Under the optimal conditions, we analyzed cocaine in a human urine sample prepared using off-line SPE to minimize the influence of the matrix. The recovery of the SPE efficiency was satisfactory (ca. 74.9-87.6%). Our experimental results suggest that, under the optimal conditions, the CSEI-sweeping-MEKC method can be used to determine cocaine and its metabolites with high sensitivity in human urine.
我们采用了一种高灵敏度的在线预富集方法——阳离子选择性完全进样（CSEI）和吹扫胶束电动色谱（MEKC），用于分析可卡因、苯甲酰爱康宁、去甲可卡因和可口卡因。我们监测了几个CSEI-吹扫-MEKC参数的影响，包括pH值、十二烷基硫酸钠（SDS）和有机改性剂的浓度、高电导率缓冲液的进样长度以及样品的进样时间，以优化分离过程。最佳背景电解质（BGE）是100 mM磷酸（pH 1.8），含有75 mM SDS，以及10%异丙醇和10%四氢呋喃作为有机改性剂。此外，在15 kV下对样品进行900 s的电动进样，可提供高分离效率和增强的吹扫灵敏度。可卡因、去甲可卡因和可口卡因的灵敏度增强范围为2.06×10⁴至3.96×10⁴；苯甲酰爱康宁为1.75×10³；测定系数超过0.9958。基于3:1的信噪比，吹扫-MEKC的检测限范围为33.5至52.8 ng/mL；相比之下，使用CSEI-吹扫-MEKC时，灵敏度提高到29.7至236 pg/mL。在最佳条件下，我们分析了使用离线固相萃取（SPE）制备的人尿样中的可卡因，以尽量减少基质的影响。SPE效率的回收率令人满意（约74.9 - 87.6%）。我们的实验结果表明，在最佳条件下，CSEI-吹扫-MEKC方法可用于高灵敏度地测定人尿中的可卡因及其代谢物。
