A Personal Computer-Based System for Interpretation of Gas Chromatography Mass Spectrometry Data in the Diagnosis of Organic Acidaemias

Abstract

Gas chromatography mass spectrometry (GCj MS) has greatly contributed to the diagnosis of inborn errors of metabolism, especially organic acidaemias. The interpretation of GCjMS data, however, is often complicated. Although some programs for automated metabolic profiling of GCjMS data have been reported, the interpretation of the GCjMS data, especially in cases with complicated profiles, may still be laborious. Therefore, we have developed a personal computer-based system for interpretation of GCjMS data for the diagnosis of organic acidaemias, based upon the categorization of metabolites flagged as abnormal above a cut-off value. To urine samples containing 1·8mmol of creatinine, 20/lg each of margaric acid (MGA) and tetracosane were added as internal standards. The samples were oximated and extracted with ethylacetate and diethylether after acidification. The organic phase was dried under nitrogen stream and the residue was trimethylsililated by N, O-bis(trimethylsilyl)-fluoroacetamide and trimethylchlorosilane (10:1, v:v). A capillary GC/ MS system (Shimadzu model QP 5000, Shimadzu Co Ltd, Kyoto, Japan) equipped with a class 5000 data processing system was used. The column was a fused silica DB-5 (30 m x 0·25 mm i.d.) with a l um film thickness of 5% phenylmethyl silicone (J&W, Folsom CA, USA). Mass spectrum were obtained by standard electron impact ionization scanning at the rate of 0-4 s/ cycle from m/z 50 to m/z 600. The temperature program was started at 100°C with initial holding for 4 min, and was increased at the rate of 4°Cjmin to 290°C, with final holding for 10min. The temperatures of the injection port and transfer line were both 280 The flow rate of the helium carrier was I·5mL/min and the linear velocity was 40·2 tnl». One microlitre of