Diagnosis of maple syrup urine disease by determination of l-valine, l-isoleucine, l-leucine and l-phenylalanine in neonatal blood spots by gas chromatography–mass spectrometry

A novel method was developed for the diagnosis of maple syrup urine disease (MSUD) by the determination of l-valine, l-leucine, l-isoleucine and l-phenylalanine in dried blood spots of newborns by gas chromatography–mass spectrometry (GC–MS). The four amino acids were extracted from blood samples by methanol and derivatized by n-butanol and trifluroacetic anhydride under optimum reaction conditions. The corresponding single derivatives of the four amino acids were obtained under the optimum conditions. Their contents in blood samples were analyzed quantitatively by measurement of their derivatives by GC–MS in selected ion monitoring mode. MSUD can be diagnosed on the basis of the ratio of the total content of l-leucine and l-isoleucine to that of l-phenylalanine. The present method only took a short time to perform and required minimal sample preparation, which provided low detection limits and a relative standard deviation of less than 5.0%. The derivatization reactions of the four amino acids, l-valine, l-isoleucine, l-leucine and l-phenylalanine, with n-butanol and trifluroacetic anhydride were investigated and the optimum reaction conditions, including reaction time and temperature, were obtained and used for the determination of the amino acids in plasma samples.