Novel, trifunctional diamine for silica coating in capillary zone electrophoresis

A novel compound {quaternarized piperazine (N-methyl,N-4-iodobutyl)-N'-meth ylpiper (QPzI)} for the coating of a silica capillary able to reduce or inv ert the electroosmotic flow (EOF) in capillary zone electrophoresis is repo rted. Unlike standard oligoamines (like spermine and tetraethylene pentamin e) which are very efficient in quenching macromolecule interaction with the silica wall, but only in acidic pH ranges, QPzI acts all along the pH scal e, including alkaline pH ranges. It is believed that QPzI behaves like a tr ifunctional derivative: it forms ionic bonds with dissociated silanols via its quaternary nitrogen, hydrogen bonds via its tertiary nitrogen and, most importantly, a covalent bond via alkylation of ionized silanols through th e terminal iodine atom in the butyl chain. Excellent separations are obtain ed with a variety of organic compounds, such as aromatic carboxylic acids, tryptophan metabolites and arylalkanoic acids. Such separations could not b e obtained in naked capillaries in the presence of oligoamines and on some occasions not even with capillaries coated with a covalent layer of neutral polymers. In separations taking place in alkaline media, QPzI is not added to the background electrolyte, but is used simply in the capillary pre-con ditioning step, a unique feature strongly supporting the hypothesis of its covalent binding to the silica surface. In difficult separations, such as i n the case of o-/p-OMe-phenylacetic acids or nicotinic/picolinic acid, whic h would not normally occur under standard conditions, it is believed that Q PzI acts as a discriminator, thus playing an active role in the separation process, rather than simply modulating the EOF. (C) 2000 Elsevier Science B .V. All rights reserved.