Esaka Yukihiro, Sawamura Mika, Murakami Hiroya, Uno Bunji
Gifu Pharmaceutical University, 5-6-1 Mitahora-higashi, Gifu 502-8585, Japan.
Anal Chem. 2006 Dec 1;78(23):8142-9. doi: 10.1021/ac061557l.
Surfactant gradient methods for electrokinetic separation of 10 benzoates as model organic anions were investigated using mixed micellar solutions of cetyltrimethylammonium chloride (CTAC) and nonionic surfactants possessing polyoxyethylene chains, polyoxyethylene sorbitan monolaurate (Tween 20) or polyoxyethylene lauryl ether (Brij 35). Electroosmotic flow (EOF) was eliminated virtually by a coating of the inner wall of the capillaries, and then the benzoates were detected fundamentally in the order of their hydrophobicity. In a pure CTAC system, the synergistic influences of attractive electrostatic and hydrophobic interactions gave rise to quite large retention factors of many of the benzoate anions, resulting in their coelution. Addition of an adequate amount of Tween 20 to the pure CTAC system decreased the electrostatic interaction significantly to give remarkably improved separation of the analytes, but long analysis time was required. A surfactant gradient method would be useful to decrease analysis time and to improve separation simultaneously. Under slight EOF, the micelles in the inlet reservoir can pass through and, thus, interact with all of the analytes before they were detected. In the present system, surfactant gradient separations could be performed simply by changing compositions of the surfactant solutions in the inlet reservoir during a single run. Additionally, we carried out continuous gradient separation using a simple device. Brij 35 gave an effect parallel to that by Tween 20 in migration behavior of the analytes. A practically negligible change in the level of the baseline was observed in a stepwise gradient elution with the CTAC/Brij 35 system because of the small absorbance at the detection wavelength, while that with the CTAC/Tween 20 was considerable. All the benzoates were separated completely within reasonable analysis times using both stepwise and continuous gradient programs for the concentrations of Tween 20 or Brij 35 in the presence of 100 mM CTAC.
以十六烷基三甲基氯化铵（CTAC）与含有聚氧乙烯链的非离子表面活性剂（聚氧乙烯山梨醇酐单月桂酸酯（吐温20）或聚氧乙烯月桂醚（Brij 35））的混合胶束溶液为研究对象，考察了用于电动分离10种作为模型有机阴离子的苯甲酸盐的表面活性剂梯度方法。通过对毛细管内壁进行涂层，基本消除了电渗流（EOF），然后根据苯甲酸盐的疏水性顺序对其进行了基本检测。在纯CTAC体系中，有吸引力的静电相互作用和疏水相互作用的协同影响导致许多苯甲酸盐阴离子具有相当大的保留因子，从而导致它们共洗脱。向纯CTAC体系中加入适量的吐温20可显著降低静电相互作用，从而显著改善分析物的分离效果，但需要较长的分析时间。表面活性剂梯度方法有助于同时减少分析时间和改善分离效果。在轻微的电渗流条件下，进样池中胶束可以通过，从而在检测之前与所有分析物相互作用。在本体系中，只需在一次运行过程中改变进样池中表面活性剂溶液的组成，即可简单地进行表面活性剂梯度分离。此外，我们使用简单装置进行了连续梯度分离。Brij 35在分析物迁移行为方面产生了与吐温20类似的效果。在CTAC/Brij 35体系的梯度洗脱中，由于检测波长处吸光度较小基线水平的变化几乎可以忽略不计，而CTAC/吐温20体系的变化则较为明显。在100 mM CTAC存在下，使用吐温20或Brij 35浓度的逐步梯度和连续梯度程序，所有苯甲酸盐均在合理的分析时间内完全分离。
