XDH and gout: In this study, a new method based on immobilized metal affinity chromatography (IMAC) combined with ultrafiltration-ultra performance liquid chromatography-mass spectrometry (UF-UPLC-MS) was developed for discovering ligands for xanthine oxidase (XO) in Gnaphalium hypoleucum DC., a folk medicine used in China for the treatment of gout.