omega-Iodoalkylammonium salts as permanent capillary silica wall modifiers- Comparative analysis of their structural parameters and substituent effects

Following previous work on the modification and inversion of electroendoosm otic flow (EOF) of naked silica by a cyclic diamine [1-(4-iodobutyl)-1,4-di methylpiperazin-1-ium iodide] [J. Chromatogr. A 894 (2000) 53], the present report considerably expands previous data by describing additional compoun ds of the same series of omega -iodoalkylammonium salts. Four of them are a ble to instantaneously reverse the EOR thus producing a cationic surface wi th a highly stable reverse EOF. All these compounds are believed to become covalently attached to the silica surface via alkylation occurring by nucle ophilic substitution of ionized silanols on the silica wall by the omega -i odo functionality in the modifier. The unique advantage of such compounds, as compared to adsorbed polymers or oligoamine EOF quenchers, is that they are not needed any longer in the background electrolyte. after the initial conditioning step inducing the covalent bond. It is additionally demonstrat ed, by running a mixture of cinnamic acid compounds, that some of the w-iod oalkylammonium salts can act as modulators of analyte migration, thus induc ing separations of otherwise identical compounds, such as isomeric species. Such interactions can only occur when the analytes drift close to the sili ca wall, and must be rapidly reversible, since no peak tailing or broadenin g is experienced. (C) 2001 Elsevier Science B.V. All rights reserved.