Quantification of D-Lactic Acid Content in PLA

The evaluation of D-lactic acid presence is very important, especially if the PLA product will be in contact with food or is a biological implant. The daily allowable intake of D-lactic acid in adult humans is 100 mg/kg and no D-lactic acid must be found in infant food. The residual of D- and L-lactic in the PLA samples can be detected using the chiral gas chromatography (CGC) method, together witii a flame ionization detector (FID). In this method, the samples are initially hydrolyzed in methanohc potassium hydroxide and tiiis is followed by acidification under strong acid to catalyze the esterification reaction. Then, methylene chloride and water are added to the acidified solution, which separate 

PLA sample is dissolved in methanolic potassium hydroxide solution at 65°C. 

Sulfuric acid is added to the sample solution and heated to 65°C again. 

The liquid sample is left to separate into two layers. 

The bottom layer of the sample is drawn up and analyze with GC—FID. 

---