Separative Determination of Mono-, Di- and Triisopropyl Citrates in Foods by Gas Chromatography

A separative determination method for mono-, di- and triisopropyl citrates in foods was developed by gas chromatography (GC). Authentic mono-, di- and triisopropyl citrates were synthesized, purified and used as standard materials.Isopropyl citrates in edible oil were directly dissolved in n-hexane. Isopropyl citrates in butter or milk powder were extracted with ethyl acetate under acidic conditions. In order to separate mono- and diisopropyl citrates, the organic solution was shaken with 5% sodium bicarbonate and then the alkaline aqueous layer was adjusted to pH 1.0 and the isopropyl citrates were reextracted with ethyl acetate. On the other hand, the ethyl acetate containing triisopropyl citrate was evaporated and the residue was taken up in n-hexane, then the triisopropyl citrate in n-hexane was extracted into acetonitrile. After evaporation of the solvent, the mono- and diisopropyl citrates were methylated with diazomethane, then they and the triisopropyl citrate were determined by GC.Recoveries of isopropyl citrates from edible oil, butter and milk powder by this method were more than 91.4%. The detection limits of isopropyl citrates were 1μg/g of sample.