... Journal of Labelled Compounds and Radiopharmaceuticals. ... J Label Compd Radiopharm, 42: 207–213. ... The two major metabolites of ibuprofen, 2-[4-(2-carboxypropyl)phenyl]propionic acid and 2-[4-(2-methyl-2-hydroxypropyl)phenyl]propionic acid, were labelled with tritium. ...