Isolation of the main organic acids from fruit juices and nectars for carbon isotope ratio measurements

A method was developed for the quantitative separation and isolation of organic acids consisting of a three step clean-up procedure (C18 tube, cation exchange and anion exchange column) and subsequent liquid Chromatographic separation on a reversed-phase column. The complete recovery of the total acids from standard juices (0.8–1 g per 20–100 ml) is between 72.6 (l-malic acid) and 73.3% (citric acid) and the δ13C value difference between applied and isolated material does not exceed 0.3‰. An isotope discrimination of the eluted acids between begin and end of a peak in reversed-phase chromatography is between 1.3 and 2.2‰, while with ion exchange chromatography this is much larger (26.3–37.9‰). Upon the experiences obtained, isotope discriminations implied in Chromatographic separations are discussed with regard to practical aspects.