Evaluation of a monolithic silica column operated in the hydrophilic interaction chromatography mode with evaporative light scattering detection for the separation and detection of counter-ions

Solvent enhanced ion chromatography of alkaline earth and transition metal ions on porous monolithic silica

“…Theory of HILIC also states that retention can be governed through the partition of polar analytes into an enriched stagnant water layer on the stationary phase surface. Through increasing the organic content of the mobile phase, this partition coefficient is increased for polar solutes, resulting in increased retention [14]. The retention behaviour seen with HILIC is the opposite to that of reversed-phase liquid chromatography and similar to normal phase selectivity, although the high water content of the mobile phase means improved solubility for polar analytes.…”

“…Alternatively, an increase of acetonitrile content in water based mobile phases has been shown to produce the opposite effect of increasing retention [18,19]. With this in mind, it is therefore proposed here that what was actually observed by Pack and Risley [14] was in fact solvent enhanced ion-exchange interactions and, correspondingly the separation mode is solvent enhanced ion chromatography (SEIC) rather than HILIC.…”

“…In the case of the separation of small ions on polar stationary phases, as in the experiments described by Pack and Risley using porous monolithic silica [14], the above explanation of retention behaviour may not be entirely suitable. Pack and Risley showed that retention of the alkali cations was dependent upon % organic solvent, ionic strength and mobile phase pH.…”

“…In the work presented here, the solvent affect described by Pack and Risley [14] is investigated further through application to alkaline earth and transition/heavy metal cations. The ability to efficiently and rapidly separate the full suite of common transition and heavy metal cations is still a challenging task and the ability to utilise simple silica monoliths for this purpose has clear advantages [23].…”

“…Detection was achieved using evaporative light scattering detection (ELSD) and the technique was applied to the determination of alkali metal counter ions in a number of pharmaceutical preparations [14]. The authors described the separation as being based upon hydrophilic interaction chromatography (HILIC).…”