A 2H nuclear magnetic resonance study of the state of water in neat silica and zwitterionic stationary phases and its influence on the chromatographic retention characteristics in hydrophilic interaction high-performance liquid chromatography.

2H NMR has been used as a tool for probing the state of water in hydrophilic stationary phases for liquid chromatography at temperatures between -80 and +4 °C. The fraction of water that remained unfrozen in four different neat silicas with nominal pore sizes between 60 and 300 Å, and in silicas with polymeric sulfobetaine zwitterionic functionalities prepared in different ways, could be determined by measurements of the line widths and temperature-corrected integrals of the 2H signals. The phase transitions detected during thawing made it possible to estimate the amount of non-freezable water in each phase.

Differences in porous characteristics of styrenic monoliths prepared by controlled thermal polymerization in molds of varying dimensions.

Nitroxide-mediated polymerization was used as a model system for preparing styrenic monolithic materials with significant mesopore contents in different mold formats, with the aim of assessing the validity of pore characterization of capillary monoliths by analysis of parallel bulk polymerized precursor solution. Capillary monoliths were prepared in 250 microm id fused silica tubes (quadruplicate samples, in total 17 m), and the batch polymerizations were carried out in parallel in 100 microL microvials and regular 2 mL glass vials, both in quintuplicate. The monoliths recovered from the molds were characterized for their meso- and macroporous properties by nitrogen sorptiometry (three repeated runs on each sample), followed by a single analysis by mercury intrusion porosimetry.

Grafting of silica with sulfobetaine polymers via aqueous reversible addition fragmentation chain transfer polymerization and its use as a stationary phase in HILIC.

Porous silica particles of 3 microm diameter and 100 A nominal pore size were first activated for vinylic polymerization by functionalization with 3-methacryloyloxypropyl trimethoxysilane (MAPTMS) and thereafter dressed with zwitterionic grafts of the sulfoalkylbetaine type in the "grafting through" fashion by polymerizing 3-(2-(N-methacryloyloxyethyl)-N,N-dimethylammonio)propane sulfonate (SPE), using either free radical polymerization or controlled reversible addition fragmentation chain transfer polymerization (RAFT). Particles polymerized using RAFT had a lower overall coating which seemed to be more evenly distributed in the pore volume. Both approaches resulted in columns with similar separation properties in HILIC mode.