Towards a microchip‐based chromatographic platform. Part 2: Sol‐gel phases modified with polyelectrolyte multilayers for capillary electrochromatography

Abstract

The potential for using polyelectrolyte multilayers (PEMs) to provide chromatographic functionality on continuous silica networks created from sol-gel chemistry has been evaluated by capillary electrochromatography (CEC). Construction of the PEM was achieved by flushing the column with polyelectrolytes of alternative charge, with variation of the properties of the exposed polyelectrolyte providing a unique means to vary the chromatographic surface. Variation of the exposed polyelectrolyte from poly(diallyldimethylammonium chloride) (PDDAC) to dextran sulfate (DS) allowed the direction of the electroosmotic flow (EOF) to be changed and also provided a means to vary the chromatographic capacity. Variation of negative polymer from DS to poly(styrene sulfonate) (PSS) significantly altered the EOF and the migration of peptides, with both the reversed-phase and ion-exchange capacities increasing. An alternative method for changing the column capacity was to change the thickness of the PEM, which was evaluated by anion-exchange CEC. A 70-80% increase in retention was observed for all anions without any increase in EOF suggesting significant penetration of the analytes through the PEM and interaction with buried charges within the PEM.

Silica‐based monoliths for capillary electrochromatography: Methods of fabrication and their applications in analytical separations

“…Breadmore et al [97] improved on their previous investigation of potential microchip sol-gels [96] discussed above, by constructing highly stable polyelectrolyte multilayers (PEMs) of PDDAC and dextran sulfate (DS) on the surface of their monoliths. These alternating layers of oppositely charged polyelectrolytes greatly enhance coating stability compared to single-layer varieties.…”

Recent applications in capillary electrochromatography

“…Differences in efficiency of columns prepared with PEO of different molecular weight were observed, which was attributed to the differences in gel structure. This group also investigated the feasibility of using a solgel silica monolith with a polyelectrolyte multiplayer (PEM) coating [113]. They observed two ways to influence the capacity of the column.…”

“…Breadmore et al [112,113] investigated the implementation of sol-gel stationary phases for CEC on a microchip. This group prepared silica monolithic stationary phases from alkyl silane, tetramethyl orthosilicate, by introducing polyethylene oxide (PEO) [114].…”

Monolithic stationary phases for fast ion chromatography and capillary electrochromatography of inorganic ions

“…In a continuation of this study, Breadmore et al [49] employed polyelectrolyte multilayers (PEM) consisting of PDDAC and dextran sulphate for use as ion-exchange stationary phases in CEC. The successive coating of an in situ synthesised silica monolith with multiple ionic polymers significantly enhanced the coating stability compared to single-layer coatings, providing highly reproducible EOF, even for columns prepared from different sol-gel batches.…”