Surfactant Gradient Methods Using Mixed Systems of Cethyltrimethylammonium Chloride and Nonionic Surfactants Possessing Polyoxyethylene Chains for Electrokinetic Separation of Benzoate Anions as Model
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- 作者：Yukihiro Esaka ; Mika Sawamura ; Hiroya Murakami ; Bunji Uno
- 刊名：Analytical Chemistry
- 出版年：2006
- 出版时间：December 1, 2006
- 年：2006
- 卷：78
- 期：23
- 页码：8142 - 8149
- 全文大小：173K
- 年卷期：v.78,no.23(December 1, 2006)
- ISSN：1520-6882
文摘
Surfactant gradient methods for electrokinetic separationof 10 benzoates as model organic anions were investigatedusing mixed micellar solutions of cetyltrimethylammonium chloride (CTAC) and nonionic surfactants possessing polyoxyethylene chains, polyoxyethylene sorbitan monolaurate (Tween 20) or polyoxyethylene lauryl ether (Brij35). Electroosmotic flow (EOF) was eliminated virtuallyby a coating of the inner wall of the capillaries, and thenthe benzoates were detected fundamentally in the orderof their hydrophobicity. In a pure CTAC system, thesynergistic influences of attractive electrostatic and hydrophobic interactions gave rise to quite large retentionfactors of many of the benzoate anions, resulting in theircoelution. Addition of an adequate amount of Tween 20to the pure CTAC system decreased the electrostaticinteraction significantly to give remarkably improvedseparation of the analytes, but long analysis time wasrequired. A surfactant gradient method would be usefulto decrease analysis time and to improve separationsimultaneously. Under slight EOF, the micelles in the inletreservoir can pass through and, thus, interact with all ofthe analytes before they were detected. In the presentsystem, surfactant gradient separations could be performed simply by changing compositions of the surfactantsolutions in the inlet reservoir during a single run.Additionally, we carried out continuous gradient separation using a simple device. Brij 35 gave an effect parallelto that by Tween 20 in migration behavior of the analytes.A practically negligible change in the level of the baselinewas observed in a stepwise gradient elution with theCTAC/Brij 35 system because of the small absorbance atthe detection wavelength, while that with the CTAC/Tween20 was considerable. All the benzoates were separatedcompletely within reasonable analysis times using bothstepwise and continuous gradient programs for the concentrations of Tween 20 or Brij 35 in the presence of 100mM CTAC.