Objective: Method for determination of orotic acid in urine gas chromatography-mass spectrometry is presented. Method: Orotic acid is isolated by ion exchange SPE extraction, derivatized by diazomethane and analysed by GC-MS. Results: GC-MS chromatograms were evaluated in Single Ion Monitoring (SIM) mode for the target ion 82 m/z. Linearity of the method was proved in the range 1.5 to 1001.5 µmol/l. Results from patient samples were in a good agreement with results obtained by capillary electrophoresis. Conclusion: Method is selective, sensitive and reproducible for rapid determination of pathological as well as physiological levels of orotic acid in urine.

        Key words: orotic acid, gas chromatography, orotic aciduria, diazomethane and inherited disorders.