Enhancement of electroosmotic flow using zwitterionic additives

Zwitterionic additives provide a means of altering the EOF without increasing conductivity. The magnitude of the EOF in a bare silica capillary increased by as much as 69% upon addition of 500 mM of zwitterion to the running buffer. The EOF enhancement increases linearly with the zwitterion concentration. With zwitterionic additives of the form +NH3-(CH2)(n)-COO-, the magnitude of the EOF increase is directly related to the number of methylene groups, (n), which ranges from n = 1 to 7. The endgroups on the zwitterions also affect the EOF enhancement. The effect of Z1-methyl (N+(CH3)(3)CH2CH2CH2SO3-) on EOF was not a function of either the buffer cation or pH. The EOF enhancement is a function of the dielectric increment of the additive and the nature of the amine functionality.