Extraction, Derivatization, and Gas Chromatography
For the methylmalonic acid standard, 25 µl of PDA in ethyl acetate were aliquoted into a glass culture tube and the solvent was evaporated under a gentle nitrogen stream at 60 °C. The tube was then capped with a rubber serum stopper and 100 µl of trimethylsilyl (TMS) were injected through the stopper. The mixture was mixed on a vortexer and heated at 60 oC for 30 mm in a hot water bath. The samples were kept at room temperature until analyzed. One µl of the prepared sample was taken through the stopper using a 10 µl Hamilton syringe and injected into the GC.