BACKGROUND LC-MS/MS with multiple reaction monitoring (MRM) is a powerful tool for quantifying target analytes in complex matrices. However, the technique lacks selectivity when plasma free metanephrines are measured. We propose the use of multistage fragmentation (MRM(3)) to improve the analytical selectivity of plasma free metanephrine measurement. METHODS Metanephrines were extracted from ...

Measurement of fractionated total metanephrines in urine provides important information for the diagnosis of pheochromocytoma (1). Reference intervals that distinguish patients who harbor a pheochromocytoma from those with similar symptoms not actually caused by this disease are highly variable (2– 4 ). Such differences may be caused by variations in analytical methods, the selection of negativ...