Determination of D-lactide content in purified L-lactide using gas chromatography-high performance liquid chromatography

A method of quantitatively determining the D-lactide content in L-lactide using combined gas chromatography(GC) and high performance liquid chromatography (HPLC) was developed. The meso-lactide and total D- and L-lactide contents were determined by separating meso-lactide from lactide using GC. However, D-lactide and L-lactide exhibited overlapping peaks in the GC curve. The D- to L-lactate unit ratio in the sample is identical to that of D- to L-lactic acid in the sample's hydrolyzate, which was quantitatively determined using chiral HPLC. Therefore, the D-lactide content can be calculated based on the GC and HPLC results. The measurement reliability was evaluated by determining the optical stability of the sample under the testing conditions and conducting parallel experiments. The lactides were hydrolyzed into lactic acid at different temperatures and different times. Lactic acid was analyzed using chiral HPLC. The D- to L-lactic acid ratio did not perceptibly change with temperature and time, thus indicating the optical stability of lactide and lactic acid under the testing conditions as well as the reliability of the measurement. The relative standard deviation of the measurements is <7.0%, indicating that the method is suitably precise. The method can be used to quantitatively determine the D-lactide content in purified L-lactide simply and accurately.