Chiral Liquid Chromatography for Resolving Malic Acid Enantiomers in Adulterated Apple Juice

Abstract
Reversed‐phase HPLC with an aqueous mobile phase containing the chiral ligand‐exchanger Cu11/ (N,N‐dimethyl‐L‐valine)2 resolved the enantiomeric a‐hydroxy acids, D‐ and L‐malate. Post‐column detection with acidic Fe111 resulted in specific detection of α‐hydroxy acids, so filtered apple juice gave a simple profile. D‐Malic acid in apple juices suspected of being adulterated with synthetic DL‐malic acid is presently determined from the difference between DL‐malic acid (HPLC assay) and L‐malic acid (L‐malate dehydrogenase assay). The potential of the chiral HPLC method relative to the indirect method was evaluated and additional possibilities for direct and more sensitive determination of D‐malate were suggested.