2-Methylenesuccinic Acid-13C5; 2-Propene-1,2-dicarboxylic Acid-13C5; 4-Hydroxy-2-methylene-4-oxobutanoic Acid-13C5; Methylenebutanedioic Acid-13C5; Methylenesuccinic Acid-13C5; NSC 3357-13C5; Propylenedicarboxylic Acid-13C5,Itaconic Acid Stable Isotopes