Homovanillic acid (HVA) is measured in urine by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Octadecyl (C18) solid-phase extraction is performed on a 1.2-mL aliquot of urine from a 24-hour collection. The solid-phase extraction column is eluted with 1.0-mL methanol. The eluate is evaporated at 30 to 40 degrees C under nitrogen, and the residue is reconstituted in 1.0 mL LC-MS/MS mobile phase. LC-MS/MS is performed by injecting 10 microL of the reconstituted specimen onto an amide-C16 HPLC column. The mobile phase (30% acetonitrile in 0.05% aqueous acetic acid) is pumped over the HPLC analytical column at the rate of 1.0 mL/min, with the flow diverted to the MS/MS electrospray probe tip by 1:5. HVA elutes apart from the bulk of the specimen matrix at a retention time of approximately 1.5 minutes. HVA is quantitated by using custom-synthesized stable isotope-labeled internal standard (C-4-hydroxy-O-HVA) from calibration over a concentration range of 1.04 to 16.7 mg/L.(Magera MJ, Stoor A, Helgeson JK, et al: Determination of homovanillic acid in urine by stable isotope dilution and electrospray tandem mass spectrometry. Clin Chim Acta 2001;306:35-41)
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