Applied Chemistry, Department of Chemistry and Chemical Engineering, Graduate School of Engineering, Hiroshima University, Japan.
Electrophoresis. 2009 Oct;30(20):3534-9. doi: 10.1002/elps.200900198.
Electrokinetic supercharging (EKS) is defined as a technique that combines electrokinetic sample injection with transient ITP. Quantitative repeatability of EKS-CZE and the other CE methods using electrokinetic sample injection process is usually inferior in comparison with the CE methods using hydrodynamic or hydrostatic injection. This is due to some effects, such as the temperature change and the convection of the sample solution in the reservoir, as well as the change of the distance between an electrode and a capillary end (D(ec)). In particular, we have found that the D(ec) change might most seriously affect the repeatability, especially when the electrode is a thin Pt wire that could be unintentionally bent during sampling. By using a Teflon spacer to fix D(ec) to 1.1 mm, the RSD of peak area (n=5) was decreased from 20 to 3.4% in EKS-CZE for several metal cations. This D(ec) dependence of the sample amount injected was supported by computer simulation using CFD-ACE+ software. The improved repeatability (down to 5.1% at n=5, averaged RSD for Co(2+), Li(+), Ni(2+), Zn(2+) and Pb(2+)) was also experimentally attained by increasing the D(ec) to ca. 20 mm, which was also effective to obtain high sensitivity. Since the temperature and the convection effects on the repeatability are comparatively small in a proper laboratory environment, these effects were estimated from the EKS-CZE experiments using conditions such as warming and agitating the sample solution during EKS process. Finally, EKS-CZE was applied to the detection of ions from atmospheric electrolytes in high-purity water exposed to ambient air for 2 h. The microgram per liter levels of anions (chloride, sulfate, nitrate, formate, acetate and lactate) and cations (ammonium, calcium, sodium and magnesium) could be detected using conventional UV detector.
电动强化（EKS）被定义为一种将电动样品注入与瞬态 ITP 相结合的技术。与使用电动进样过程的 CE 方法相比，EKS-CZE 和其他使用电动进样过程的 CE 方法的定量重复性通常较差。这是由于一些影响，例如储液器中样品溶液的温度变化和对流，以及电极和毛细管末端之间的距离（D(ec)）的变化。特别是，我们发现 D(ec)的变化可能会严重影响重复性，尤其是当电极是一根薄的 Pt 丝时，在采样过程中可能会意外弯曲。通过使用聚四氟乙烯间隔物将 D(ec)固定在 1.1mm，可以将几种金属阳离子的 EKS-CZE 中峰面积的 RSD（n=5）从 20%降低到 3.4%。使用 CFD-ACE+软件进行的计算机模拟支持这种对注入样品量的 D(ec)依赖性。通过将 D(ec)增加到约 20mm，还可以获得更高的灵敏度，同时也可以提高重复性（n=5 时降至 5.1%，Co(2+)、Li(+)、Ni(2+)、Zn(2+)和 Pb(2+)的平均 RSD）。在适当的实验室环境中，由于温度和对流对重复性的影响相对较小，因此可以从 EKS-CZE 实验中使用的条件（例如在 EKS 过程中加热和搅拌样品溶液）中估算这些影响。最后，将 EKS-CZE 应用于检测在大气中暴露 2 小时的高纯水的大气电解质中的离子。可以使用常规的 UV 检测器检测微克/升水平的阴离子（氯离子、硫酸盐、硝酸盐、甲酸盐、乙酸盐和乳酸盐）和阳离子（铵、钙、钠和镁）。
