A non-destructive test to assess the axial heterogeneity of in situ modified monoliths for HPLC

Abstract

A multi-location peak parking protocol was developed for a non-destructive assessment of the axial heterogeneity of in situ modified monoliths. This was tested on a column with a surface coverage density gradient along the length of the monolithic rod. Qualitative changes in band broadening were observed and were consistent with theoretical studies.

Amine Gradient Stationary Phases on In-House Built Monolithic Columns for Liquid Chromatography

“…Recently, a few reports of continuous gradient stationary phases have appeared in the literature as a means to improve the selectivity of separations. − Our group, for example, has demonstrated the usefulness of continuous stationary phase gradients in thin layer chromatography (TLC) plates via separation of mixtures of acids and bases, over the counter drugs, water and fat-soluble vitamins, and metal ions. − Gradient stationary phases have also been prepared on polymeric capillary monoliths for electrochromatography. ,, These gradient stationary phases showed better performance and resolution of solutes compared to homogeneously modified stationary phases. Bassanese et al have recently reported the modification of a commercial silica monolithic column to form a gradient stationary phase, which they claimed gave different efficiencies, depending on the direction of the flow relative to the gradient direction; however, this observation goes against well-established theory that peak compression should not occur on gradient stationary phases . In this particular study, only one commercial column was modified, the results from the elemental characterization of the gradient profile were inconclusive, and no comparisons made to results obtained on uniformly modified columns.…”

“…13,14,18 These gradient stationary phases showed better performance and resolution of solutes compared to homogeneously modified stationary phases. Bassanese et al have recently reported the modification of a commercial silica monolithic column to form a gradient stationary phase, which they claimed gave different efficiencies, depending on the direction of the flow relative to the gradient direction; 19 however, this observation goes against well-established theory that peak compression should not occur on gradient stationary phases. 20 In this particular study, only one commercial column was modified, the results from the elemental characterization of the gradient profile were inconclusive, and no comparisons made to results obtained on uniformly modified columns.…”

Impact of particle size gradients on the apparent efficiency of chromatographic columns

“…Pucci et al, first applied continuous stationary phase gradients by photografting ionizable chains onto a hydrophobic polymer monolithic in a gradient fashion for capillary electrochromatography [14]. Since then, continuous stationary phase gradients have been applied in thin layer chromatography (TLC) and also for silica monoliths used in LC [11,15,16,17]. Very recently, the principles of so-called controlled rate of infusion (CRI) were adapted to develop a new approach to fabricate continuous stationary phase gradients on packed columns [13].…”

In situ silanization for continuous stationary phase gradients on particle packed LC columns

“…The benets of varying the ligand concentration along the length of column were rst observed in the early 1990s with serially coupled columns 1-6 (i.e., a discontinuous stationary phase gradient); however, the creation of a gradient on a continuous stationary support for LC did not come about until 2007, when Fanali et al lled a capillary with solutions of decreasing hydrophilicities and used thermal polymerization to produce a stationary phase with a continuous hydrophobic gradient. 7 Since this work, the fabrication of continuous gradients in the stationary phase for LC has almost exclusively involved monoliths (polymer 7-11 and silica 11,12 ), likely due to challenges associated with the formation of a gradient in chemical functionality on particle packed columns. To our knowledge, only one report has appeared on a continuous stationary phase gradient on a particle packed column.…”