Quantification of methylmalonic acid in serum measured by capillary gas chromatography—mass spectrometry as tert.-butyldimethylsilyl derivatives Journal of Chromatography: Biomedical Applications, Volume 620, Issue 1, 22 October 1993, Pages 1-7 Jean Straczek, Franck Felden, Brigitte Dousset, Jean Louis Gueant, Francine Belleville