When working with standard C18 phases in an aqueous environment (less than 5 % of organic solvent) we face undesired effects like peak broadening, tailing and erratic retention times. These effects are associated to the phase collapse of the C18 chains. Thanks to the unique bonding technique on the C18 AQ phase, we can work with pure water and we get more symmetric peaks. Besides this, we get a better retention in aqueous eluents. This leads to an extended selectivity compared to standard C18 material. For the separation of highly polar substances we can use the advantages of the C18 AQ. Typical applications are the separation of water soluble vitamins and organic acids.