POBN (4-POBN) is a cell permeable, hydrophilic spin trap that can be used to detect free radical adducts.In Vitro: When POBN (20 mM) and Sodium formate (100 mM) are mixed in the collecting tube with bile in the presence of 2,2′-dipyridyl (DP) (5 mM) and bathocuproinedisulfonic acid disodium salt hydrate (BC) (5 mM), only a minor residual signal of POBN radical adduct is observed.In Vivo: Electron spin resonance (ESR) spectrum of radical adducts detected in bile of rats 1 h after acute Sodium formate (2 g/kg) and POBN (1.5 g/kg) i.p. administration.