Foley Joe P, Hong Mei, Polinko Michelle A, Pascoe Robert J, Ahuja Eric S
Department of Chemistry, Drexel University, Philadelphia, PA, USA.
Electrophoresis. 2008 Mar;29(5):1180-8. doi: 10.1002/elps.200700809.
The effect of the phase ratio on the electrophoretic and chromatographic properties of unilamellar vesicles comprised of cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) was investigated in EKC. The surfactant concentration of the vesicles was 0.9, 1.2, 1.5, and 1.8% w/v, with a mole ratio of 1:3.66 (CTAB/SOS). Results were compared to those obtained using SDS micelles at concentrations of 1.0% (w/v, 35 mM) and 1.5% (52 mM). The CTAB/SOS vesicles (0.9-1.8% w/v) provided a significantly larger elution range (5.7 < or = t(ves)/t(0) < or = 8.7) and greater hydrophobic (methylene) selectivity (2.8 < or = alpha(CH2) < or = 3.1) than SDS micelles (3.1 < or = t(mc)/t(0) < or = 3.3; alpha(CH2) = 2.2). Whereas the larger elution range can be attributed to the 25% reduction in EOF due to the interaction of unaggregated CTAB cations and the negatively charged capillary wall, the higher methylene selectivity is likely due to the lower concentration of water expected in the CTAB/SOS vesicle bilayer compared to the Palisades layer of SDS micelles. For a given phase ratio, CTAB/SOS vesicles are somewhat less retentive than SDS micelles, although retention factors comparable to those observed in 1.0-1.5% SDS can be obtained with 1.5-1.8% CTAB/SOS. A linear relationship was observed between phase ratio and retention factor, confirming the validity of the phase ratio model for these vesicles. Unique polar group selectivities and positional isomer shape selectivities were obtained with CTAB/SOS vesicles, with both types of selectivities being nearly independent of the phase ratio. For four sets of positional isomers, the elution order was always para < ortho < meta. Finally, the thermodynamics of solute retention was qualitatively similar to that reported for other surfactant aggregates (micelles and microemulsions); the enthalpic contribution to retention was consistently favorable for all compounds, whereas the entropic contribution was favorable only to hydrophobic solutes.
在毛细管电泳中，研究了相比率对由十六烷基三甲基溴化铵（CTAB）和辛基硫酸钠（SOS）组成的单层囊泡的电泳和色谱性质的影响。囊泡的表面活性剂浓度为0.9%、1.2%、1.5%和1.8%（w/v），摩尔比为1:3.66（CTAB/SOS）。将结果与使用浓度为1.0%（w/v，35 mM）和1.5%（52 mM）的SDS胶束所获得的结果进行比较。CTAB/SOS囊泡（0.9 - 1.8% w/v）提供了比SDS胶束（3.1≤t(mc)/t(0)≤3.3；α(CH2)=2.2）显著更大的洗脱范围（5.7≤t(ves)/t(0)≤8.7）和更高的疏水（亚甲基）选择性（2.8≤α(CH2)≤3.1）。虽然较大的洗脱范围可归因于未聚集的CTAB阳离子与带负电荷的毛细管壁相互作用导致电渗流降低25%，但较高的亚甲基选择性可能是由于与SDS胶束的栅栏层相比，CTAB/SOS囊泡双层中预期的水浓度较低。对于给定的相比率，CTAB/SOS囊泡的保留性略低于SDS胶束，尽管使用1.5 - 1.8%的CTAB/SOS可获得与在1.0 - 1.5% SDS中观察到的保留因子相当的保留因子。观察到相比率与保留因子之间存在线性关系，证实了这些囊泡的相比率模型的有效性。使用CTAB/SOS囊泡获得了独特的极性基团选择性和位置异构体形状选择性，这两种选择性几乎都与相比率无关。对于四组位置异构体，洗脱顺序始终是对位 < 邻位 < 间位。最后，溶质保留的热力学性质在定性上与其他表面活性剂聚集体（胶束和微乳液）所报道的相似；焓对保留的贡献对所有化合物始终是有利的，而熵的贡献仅对疏水性溶质是有利的。
