School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, P R China.
Electrophoresis. 2010 Jan;31(4):672-8. doi: 10.1002/elps.200900342.
The influences of the composition of microemulsion on the microstructure including dimensions and zeta potentials of microdroplets were measured in details. The average dynamic dimension of microdroplets was measured by dynamic laser light scattering, and zeta potential was determined to characterize average surface charge density of microdroplets. The experiment results showed that increase of the amount of surfactant resulted in decrease of microdroplet size but almost invariant zeta potential, which would enlarge migration time of the microdroplet in MEEKC. With increment of cosurfactant concentration, the microdroplet size had an increasing trend, whereas the zeta potential decreased. Thus, observed migration velocity of microdroplets increased, which made the separation window in MEEKC shortened. Neither dimension nor zeta potential of microdroplets changed by varying both the type and the amount of the oil phase. Adding organic solvent as modifier to microemulsion did not change the microdroplet size, but lowered zeta potential. The migration time of microdroplet still became larger, since EOF slowed down owing to organic solvent in capillary. So, besides increment of surfactant concentration, organic additive could also enlarge the separation window. Increase of cosurfactant concentration was beneficial for separation efficiency thanks to the looser structure of swollen microdroplet, and the peak sharpening might compensate for the resolution and peak capacity owing to a narrow separation window. Except the oil phase, tuning the composition of microemulsion would change the microstructure, eventually could be exploited to optimize the resolution and save analysis time in MEEKC.
详细测量了微乳液组成对微滴的微观结构（包括尺寸和zeta 电位）的影响。通过动态激光光散射测量了微滴的平均动态尺寸，并且通过测定 zeta 电位来表征微滴的平均表面电荷密度。实验结果表明，表面活性剂的量增加会导致微滴尺寸减小，但 zeta 电位几乎不变，这会增加微滴在 MEEKC 中的迁移时间。随着助表面活性剂浓度的增加，微滴尺寸呈增大趋势，而 zeta 电位降低。因此，观察到的微滴迁移速度增加，使 MEEKC 的分离窗口缩短。改变油相的类型和数量都不会改变微滴的尺寸或 zeta 电位。向微乳液中添加有机溶剂作为改性剂不会改变微滴尺寸，但会降低 zeta 电位。由于毛细管中的有机溶剂，EOF 会减慢，因此微滴的迁移时间仍然会变大。因此，除了增加表面活性剂浓度外，有机溶剂添加剂还可以扩大分离窗口。由于溶胀微滴的结构更疏松，助表面活性剂浓度的增加有利于分离效率的提高，并且由于分离窗口较窄，峰展宽可能会弥补分辨率和峰容量的损失。除油相外，调节微乳液的组成会改变微结构，最终可以用于优化分辨率并在 MEEKC 中节省分析时间。
