Primesep B2 separates xanthines such as theobromine, dimethylxanthine, theophylline by a combination of reversed-phase and ion-exchange mechanisms. The anion-exchange properties of the column allow retention of hydrophilic xanthines, and the reversed-phase properties retain hydrophobic compounds. The HPLC separation uses a mobile phase of water, acetonitrile (MeCN, ACN) and either trifluoroacetic acid (TFA), perchloric acid (HClO4), or sulfuric acid (H2SO4) and UV detection.