Screening of Organic Acidurias by Gas Chromatography-Mass Spectrometry (GC-MS)

Organic acidurias or acidemias are a group of diverse disorders caused by decreased or diminished activity of specific enzyme or transporter involved in the metabolism of amino acids, carbohydrates, fatty acids, and nucleic acids. Organic acidurias are generally inherited but may be acquired due to deficiency of certain cofactors or vitamins. As clinical symptoms are of nonspecific nature, definitive diagnosis of organic aciduria requires measurement of organic acids in urine or blood and sometimes enzyme activity in the cells. Gas chromatography-mass spectrometry (GC-MS) is a commonly used method for screening of organic acidurias.GC-MS procedure described here involves the use of urine volume that contains 1 μmole (113 μg) of creatinine. Internal standards (tropic and 2-ketocaproic acids) are added to the samples, followed by treatment with hydroxylamine to form oxime derivatives of the ketoacids. The mixture is then acidified, and organic acids are extracted in ethyl acetate. The organic extract is concentrated to dryness, and the residue is treated with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA)/trimethylchlorosilane (TMCS)/pyridine to form the trimethylsilyl (TMS) derivatives of the organic acids. The derivatized extract is then directly injected onto GC-MS for analysis.