Fabrication and characterisation of capillary polymeric monoliths incorporating continuous stationary phase gradients

Abstract

Polymeric monoliths in capillary formats have been fabricated incorporating a gradient of charged functional groups along their length. Scanning capacitively coupled contactless conductivity detection (sC(4)D) was then used to measure the conductive response of the stationary phase and characterise the relative axial distribution of functional groups along the column length. Gradients of 2-acrylamido-2-methyl-1-propanesulphonic acid were prepared using either photografting methods or by filling a capillary column with segmented plugs of monomer mixtures each containing incrementally higher concentrations of the functional monomer. The utility of sC(4)D as a rapid and non-invasive tool for assessing the slope of a variety of gradient configurations is demonstrated. Repeatability of the sC(4)D measurements was <1.7% RSD. Columns with a gradient of covalently bonded iminodiacetic acid were also produced. Changes in the gradient slope were observed after chelation of copper on the stationary phase via a reduction of the conductive response. The effect upon the observed gradient profile of changing the co-monomer composition during column fabrication was studied.