Theoretical study on solute migration and band broadening occurring in pressure-enhanced liquid chromatography

•Migration velocity gradients were studied in pressure enhanced LC (PE-LC).•Band broadening and sharpening in pressurized separations were illustrated.•Both retention increase and decrease caused by pressure were considered.•Experiments performed at same average pressure but with different gradients. Upon recently studying the use of pressure gradients during liquid chromatography (LC), it was noted that pressure differentials across a column can have a significant impact on peak shape, not just retention as has been noted several times before. Theoretical models and thought experiments were performed here to more carefully study these effects. Two situations have been elucidated. The first is one that reflects a protein reversed phase separation wherein solute retention increases with pressure. In this condition, it has been found that a positive pressure gradient will result in band broadening while a negative pressure gradient will help yield sharper peaks. The second case that has come to be better appreciated is when solute retention decreases with pressure, which can occur in protein ion exchange (IEX) and hydrophobic interaction chromatography (HIC). In this situation, a positive pressure gradient will conversely result in peak sharpening, and a negative pressure gradient will introduce band broadening. These observations have facilitated making new fundamental understandings on pressurized separations which has in turn made it possible to begin envisioning new ways of and reasons for applying pressure enhanced LC methods.