SEARCH Articles Figures Tables 18<). isotopic labelling with Acids oxalic acid Isotope isotopic labeling Isotope label Isotope-labelled Isotopes acids Isotopic labeling Isotopic labeling with Isotopic labelled Isotopic labelling Isotopic labels Isotopical labeling Labeling with Labelled with Labelled with isotopic Oxalic acid Oxalic acid, acidity Oxalic acid/oxalate