Influence of pressure and temperature on molar volume and retention properties of peptides in ultra-high pressure liquid chromatography

In this study, pressure induced changes in retention were measured for model peptides possessing molecular weights between ∼1 and ∼4 kDa. The goal of the present work was to evaluate if such changes were only attributed to the variation of molar volume and if they could be estimated prior to the experiments, using theoretical models. Restrictor tubing was employed to generate pressures up to 1000 bar and experiments were conducted for mobile phase temperatures comprised between 30 and 80 °C. As expected, the retention increases significantly with pressure, up to 200% for glucagon at around 1000 bar compared to ∼100 bar. The obtained data were fitted with a theoretical model and the determination coefficients were excellent (r2 > 0.9992) for the peptides at various temperatures. On the other hand, the pressure induced change in retention was found to be temperature dependent and was more pronounced at 30 °C vs. 60 or 80 °C. Finally, using the proposed model, it was possible to easily estimate the pressure induced increase in retention for any peptide and mobile phase temperature. This allows to easily estimating the expected change in retention, when increasing the column length under UHPLC conditions.