Exposure and Biomonitoring Division, Health Canada, Ottawa, Ontario, Canada.
J Chromatogr A. 2011 May 20;1218(20):3095-104. doi: 10.1016/j.chroma.2011.03.017. Epub 2011 Mar 17.
The mechanism underlying the enrichment power by pressure-assisted electrokinetic injection (PAEKI) in capillary electrophoresis (CE) was investigated for on-line pre-concentration of arsenic [As(III) and As(V)], selenium [Se(IV) and Se(VI)] and bromate (BrO(3)(-)). Analyte diffusion behaviour from PAEKI sample plugs were evaluated by monitoring peak broadening as a function of stagnant time and position in the capillary. During PAEKI, anionic analytes accumulate at the sample-separation buffer boundary. We proposed that a counter-ion layer formed in PAEKI, where a cation layer was formed at the separation buffer side of boundary. The cation layer served as a soft boundary which impeded zone broadening via electrostatic attraction between layers. This effect likely played an important role in maintaining focused analyte bands by suppressing diffusion. Comparison of analyte behaviour in PAEKI injected sample plugs to behaviour in hydrodynamically injected ones proved the existence of a counter-ion layer. The dependence of analyte diffusion in PAEKI plugs on electrochemical properties (viscosity, conductivity, electrophoretic mobility) further supported the hypothesis. Additionally, it was noted that analytes with low electrophoretic mobility were more efficiently pre-concentrated by PAEKI and were less subject to forces of dispersion than analytes with greater electrophoretic mobility. PAEKI-CE coupled to electrospray tandem mass spectroscopy (ESI-MS/MS) was then optimized and validated for detection of arsenic, selenium and bromate in water samples. On-line enrichment of the target analytes was achieved with 1-3 ng mL(-1) detection limits, which was below the maximum contaminant levels in drinking water for all five anions studied. Noteworthy, the potential of the method for unbiased detection of molecular species in untreated water was demonstrated. No contamination was detected in the water samples tested; however, recovery was 90-118% for spiked samples. The method was demonstrated be comparable to current methods for detection of inorganic contaminants in drinking water and is a good alternative method to ion chromatography/liquid chromatography-MS.
压力辅助电动进样（PAEKI）在毛细管电泳（CE）中富集能力的机制被用于砷[As(III)和 As(V)]、硒[Se(IV)和 Se(VI)]和溴酸盐（BrO(3)(-)]的在线预浓缩。通过监测峰展宽作为停滞时间和在毛细管中位置的函数，评估了从 PAEKI 样品塞中分析物的扩散行为。在 PAEKI 期间，阴离子分析物在样品-分离缓冲液边界处积累。我们提出，在 PAEKI 中形成了反离子层，在边界的分离缓冲液侧形成了阳离子层。阳离子层作为软边界，通过层之间的静电吸引阻碍了区域展宽。这种效应可能通过抑制扩散在维持聚焦分析物带方面发挥了重要作用。与在水力驱动注入的样品塞中分析物行为的比较证明了反离子层的存在。在 PAEKI 塞中分析物扩散对电化学性质（粘度、电导率、电泳迁移率）的依赖性进一步支持了这一假设。此外，还注意到，具有低电泳迁移率的分析物通过 PAEKI 更有效地进行预浓缩，并且比具有更大电泳迁移率的分析物受到的分散力更小。然后，优化并验证了 PAEKI-CE 与电喷雾串联质谱（ESI-MS/MS）联用，用于检测水样中的砷、硒和溴酸盐。通过 1-3 ng mL(-1)的检测限实现了目标分析物的在线富集，这低于所有五种研究阴离子的饮用水中最大污染物水平。值得注意的是，该方法具有在未处理水中对分子物种进行无偏检测的潜力。在测试的水样中未检测到污染；然而，加标样品的回收率为 90-118%。该方法与当前饮用水中无机污染物检测方法相当，是离子色谱/液相色谱-MS 的良好替代方法。
