Mann S E, Ringo M C, Shea-McCarthy G, Penner-Hahn J, Evans C E
Department of Chemistry, University of Michigan, Ann Arbor 48109-1055, USA.
Anal Chem. 2000 Apr 15;72(8):1754-8. doi: 10.1021/ac9909608.
X-ray fluorescence spectroscopy is demonstrated here as a novel, element-specific detector for capillary electrophoresis. Monochromatic 10 keV X-rays from a synchrotron light source are used to excite core electrons, causing emission of characteristic Kalpha X-ray fluorescence (XRF) lines. Using this technique, XRF energies provide elemental identification, while XRF intensities can be used to quantitate the metal composition of each eluent. An X-ray transparent polymer coupling is used to create a window for the on-line, X-ray detection. This coupling contributes no measurable extra-column variance, and electrophoretic mobilities for the metal complexes used as model solutes are highly reproducible. The combination of XRF detection with capillary electrophoresis (CE-XRF) creates the first on-line detection system that is element-specific, nondestructive, and directly applicable to a broad range of applications including nonelectroactive species. CE-XRF is successfully demonstrated here for high binding-constant complexes of Fe(III), Co(II), Cu(II), and Zn(II). Within a single injection, electropherograms are obtained for each element of interest, with the element identity obtained directly from the emission energy. In contrast with ICPMS, this detection technique is directly on-line and does not require volatilization of the eluent. As a result, element-specific detection is not limited by the sample or the buffer volatility or atomization efficiency. Simultaneous XRF and UV absorbance detection can be used to provide an on-line determination of metal/chelate ratios. Although XRF detection limits are presently only in the 0.1 mM (0.5 ng) range, both collection geometry and incident intensity have yet to be optimized. Further optimization is expected to enhance this detection limit by another 2-3 orders of magnitude. As a result, the advent of XRF detection combined with the separating power of CE presents new possibilities for on-line, element-specific analysis.
本文展示了X射线荧光光谱法作为一种用于毛细管电泳的新型元素特异性检测器。来自同步加速器光源的单色10 keV X射线用于激发内层电子，从而产生特征性的Kα X射线荧光（XRF）谱线。利用该技术，XRF能量可用于元素识别，而XRF强度可用于定量每种洗脱液的金属成分。使用X射线透明聚合物连接件创建一个用于在线X射线检测的窗口。该连接件不会产生可测量的柱外方差，并且用作模型溶质的金属配合物的电泳迁移率具有高度可重复性。XRF检测与毛细管电泳（CE-XRF）相结合，创建了首个元素特异性、无损且直接适用于包括非电活性物质在内的广泛应用的在线检测系统。本文成功展示了CE-XRF用于Fe(III)、Co(II)、Cu(II)和Zn(II)的高结合常数配合物。在单次进样内，可获得每种感兴趣元素的电泳图，元素身份直接从发射能量获得。与电感耦合等离子体质谱法（ICPMS）相比，这种检测技术是直接在线的，不需要洗脱液挥发。因此，元素特异性检测不受样品或缓冲液挥发性或雾化效率的限制。同时进行XRF和紫外吸光度检测可用于在线测定金属/螯合物比率。尽管目前XRF检测限仅在0.1 mM（0.5 ng）范围内，但收集几何结构和入射强度均有待优化。进一步优化有望将该检测限再提高2 - 3个数量级。因此，XRF检测的出现与CE的分离能力相结合，为在线元素特异性分析带来了新的可能性。
