Covalent anionic copolymer coatings with tunable electroosmotic flow for optimization of capillary electrophoretic separations
Abstract
We present a method for finely adjustable electroosmotic flow (EOF) velocity in cathodic direction for the optimization of separations in capillary electrophoresis. To this end, we use surface modification of the separation fused silica capillary by covalently attached copolymer of acrylamide (AM) and 2-acrylamido-2-methyl-1-propanesulfonate (AMPS), i.e., poly(AM-co-AMPS) or PAMAMPS.
Coatings were formed by in-capillary polymerization of a mixture of the neutral AM and anionic AMPS monomers premixed in various ratio in order to control the charge density of the copolymer. EOF mobility varies in the 0 to TILDE OPERATOR+D9140 x 10(-9) m(2) V(-1) s(-1) interval for PAMAMPS coatings ranging from 0 to 60 mol.% of charged AMPS monomer.
For EOF in PAMAMPS treated capillaries, we observed (i) a negligible dependence on pH in the 2-10 interval, (ii) a minor variance between background electrolytes (BGEs) in function of their components and (iii) its standard decrease with increasing ionic strength of the BGE. Interest in variable cathodic EOF was demonstrated by amelioration of separation of two kinds of isomeric anionic analytes, i.e., monosaccharides phosphates and helquat enantiomers, in counter-EOF mode.