Simultaneous determination of D- and L-malic acids in apple juice by gas chromatography.

A gas chromatographic (GC) method was developed for the simultaneous determination of D- and L-malic acids in apple juice. D-Malic-(R)-(-)-2-butyl ester and L-malic-(R)-(-)-2-butyl ester are prepared with (R)-(-)-2-butanol. These diastereomers are separated and quantitated by gas chromatography on a Carbowax 20M (30 m x 0.25 mm) fused silica capillary column. This procedure does not involve any extraction or cleanup step.