Further investigations of the effect of pressure on retention in ultra-high-pressure liquid chromatography

Fallas, Morgane M.; Neue, Uwe D.; Hadley, Mark R.; McCalley, David V.

Abstract

In this study, we investigated further the large increases in retention with pressure that we observed previously in RP-LC especially for ionised solutes. These findings were initially confirmed on a conventional silica C18 column, which gave extremely similar results to the hybrid C18 phase originally used. Large increases in retention factor of ∼50% for a pressure increase of 500 bar were also shown for high MW polar but neutral solutes. However, experiments with the same bases in ionised and non-ionised forms suggest that somewhat greater pressure-induced retention increases are found for ionised solutes. Retention increases with pressure were found to be considerably smaller for a C1 column compared with a C18 column; decreases in retention with increasing pressure were noted for ionised bases when using a bare silica column in the hydrophilic interaction chromatography (HILIC) mode. These observations are consistent with the partial loss of the solvation layer in RP-LC as the solute is forced into the hydrophobic environment of the stationary phase, and consequent reduction in the solute molar volume, while the water layer on the surface of a HILIC packing increases the hydration of a basic analyte. Finally, retention changes with pressure in RP-LC can also be observed at a mobile phase pH close to the solute pKa, due to changes in pKa with pressure. However, this effect has no influence on the results of most of our studies. © 2009 Elsevier B.V. All rights reserved.

• Journal Article Type: Article
• Publication Date: Jan 15, 2010
• Journal: Journal of Chromatography A
• Print ISSN: 0021-9673
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 1217
• Issue: 3
• Pages: 276-284
• DOI: https://doi.org/10.1016/j.chroma.2009.11.041
• Keywords: retention factors, pressure, ultra-high-pressure LC
• Public URL: https://uwe-repository.worktribe.com/output/981832
• Publisher URL: http://dx.doi.org/10.1016/j.chroma.2009.11.041