Hydrophilic-lipophilic balance (HLB) solid-phase extraction (SPE) is performed on an aliquot of urine from a 24-hour collection. The SPE column is eluted with 1 mL of methanol. The eluate is evaporated at 50 degrees C under nitrogen, and the residue reconstituted in 1 mL of the liquid chromatography-tandem mass spectrometry (LC-MS/MS) mobile phase. LC-MS/MS is performed by injecting 10 mcL of the reconstituted specimen onto an amide-C16 HPLC column. The mobile phase (15% methanol in 0.05% aqueous formic acid) is pumped over the HPLC analytical column at a rate of 1.0 mL/min with the flow diverted to the MS/MS electrospray probe tip by 1:5. Vanillylmandelic acid (VMA) elutes apart from the bulk of the specimen matrix at a retention time of approximately 1.5 minutes. VMA is quantitated using a stable isotope labeled internal standard from calibration over a concentration range 1.03 to 20 mg/L.(Magera MJ, Thompson AL, Stoor AL, et al: Determination of vanillylmandelic acid in urine by stable isotope dilution and electrospray tandem mass spectrometry. Clin Chem 2003;49:825-826)
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