This page note the Retention Maps for HPS™ C18 produce exponential increases in retention times as the % organic is reduced (% Distilled Buffer Water increases) and that the pH of the eluent is changed to be acidic with little useful resolution at near neutral and basic pH. This is typical ARP and can be utilized to aid your method development of organic acids on type B reverse phase materials.

Notice that the UDC-Cholesterol™ Column Acts Differently.

At acid pH, the target organic acids act typically in ARP with the same elution order as the HPS™ C18 column with excellent peak shape plus good symmetry.

But at pH 8.00 an ANP (Aqueous Normal Phase) retention profile is shown with a reversal of elution order of the analytes.

The pH of 6.80 is transitional with a different elution order.

Thus orthogonal, confirming analysis is possible on the same UDC-Cholesterol™ column with the option to accomplish resolution by ARP with high % aqueous or ANP with low % aqueous ( better suited to prep applications ) by merely changing the pH of the eluent.