While reversed phase is the most widely used mode of retention in HPLC, very polar compounds are often not sufficiently retained in low percent organic, or even in 100% aqueous mobile phase.

By using a strongly polar bonded phase such as TSKgel Amide-80, polar compounds can be retained by a normal phase or hydrophilic interaction chromatography (HILIC; see references) retention mechanism using an mobile phase mixture of acetonitrile and ammonium acetate buffer. In contrast to the retention behavior in reversed phase, in HILIC solutes are retained longer by increasing the percent acetonitrile.