Macka M, Haddad P R, Gebauer P, Bocek P
Department of Chemistry, University of Tasmania, Hobart, Australia.
Electrophoresis. 1997 Oct;18(11):1998-2007. doi: 10.1002/elps.1150181120.
A theoretical and experimental study of the existence and evolution of system peaks in capillary zone electrophoresis (CZE) with indirect spectrophotometric detection is presented with respect to the effect of the number of coions present in the background electrolyte (BGE). It is shown that in BGEs having only one coion (i.e., the UV-absorbing probe anion), the sample produces only negative peaks due to each analyte anion and no system peaks, with the number of sample peaks corresponding to the number of analytes present in the sample injected. In BGEs containing two coions, a sample with one analyte anion produces one negative indirect detection peak and one system peak. The transition between BGEs having one coion and those with two coions has also been studied and it has been shown that an addition of ca. 5% of the second coion to a single coion BGE causes the resulting BGE to behave macroscopically as a regular two-coion BGE. A descriptive model is proposed, based on transient isotachophoresis (transient stacking) of the sample species and of the coion from the BGE which has the closest mobility to the sample ion. This model explains qualitatively the formation and evolution of the sample peak (containing the sample species and being detected by indirect detection due to displacement of the UV-absorbing probe in its zone) and the system peak (containing no sample species and being a vacancy in the continuum of coions of the BGE). It is shown that the system peak may be positive or negative as it corresponds to the situation where the vacancy of one component of the BGE results in an enhanced concentration of the other component. It has been demonstrated that the system peak is created by a vacancy of that component of the BGE which has the greatest difference in mobility relative to that of the sample species. On indirect detection in BGEs containing two coions the sample displaces predominantly the BGE coion which has a mobility closest to that of the analyte anion. In systems with BGEs containing two coions, a sample having n analytes produces n sample peaks and one system peak, the sign and magnitude of which are dependent on the sum of the UV absorbances of the analytes involved. The effect of bicarbonate from atmospheric CO2 has also been studied and it has been shown that weakly alkaline BGEs with a single anionic UV-absorbing coion, such as those currently used for anionic analyses with indirect detection, may suffer from the presence of system peaks due to bicarbonate.
针对背景电解质（BGE）中伴随离子数量的影响，开展了一项关于毛细管区带电泳（CZE）中系统峰的存在与演变的理论和实验研究，采用间接分光光度检测法。结果表明，在仅含有一种伴随离子（即紫外吸收探针阴离子）的BGE中，样品仅因每种分析物阴离子产生负峰，不存在系统峰，样品峰的数量与注入样品中分析物的数量相对应。在含有两种伴随离子的BGE中，含有一种分析物阴离子的样品会产生一个负的间接检测峰和一个系统峰。还研究了含有一种伴随离子的BGE与含有两种伴随离子的BGE之间的转变，结果表明，向单一伴随离子BGE中添加约5%的第二种伴随离子会使所得BGE在宏观上表现为常规的双伴随离子BGE。基于样品物种和来自BGE且迁移率与样品离子最接近的伴随离子的瞬态等速电泳（瞬态堆积），提出了一个描述性模型。该模型定性地解释了样品峰（包含样品物种并因紫外吸收探针在其区域内的位移而通过间接检测进行检测）和系统峰（不包含样品物种且是BGE伴随离子连续体中的一个空位）的形成和演变。结果表明，系统峰可能为正或负，因为它对应于BGE一种组分的空位导致另一种组分浓度增加的情况。已经证明，系统峰是由BGE中与样品物种迁移率差异最大的那个组分的空位产生的。在含有两种伴随离子的BGE中进行间接检测时，样品主要取代迁移率与分析物阴离子最接近的BGE伴随离子。在含有两种伴随离子的BGE系统中，含有n种分析物的样品会产生n个样品峰和一个系统峰，其符号和大小取决于所涉及分析物的紫外吸光度总和。还研究了大气CO₂中的碳酸氢盐的影响，结果表明，具有单一阴离子紫外吸收伴随离子的弱碱性BGE，如目前用于间接检测阴离子分析的那些BGE，可能会因碳酸氢盐的存在而出现系统峰。
