Determination of plasma methoxyamines

The determination of plasma methoxyamines is the most informative parameter for the diagnosis of pheochromocytoma. Very good sensitivity and specificity are necessary for this. The measurement of deconjugated (free plus sulfate-conjugated) metanephrines is more useful. Concentrations are 10-fold higher than free metanephrine concentrations. The methodology generally uses a column purification and high performance liquid chromatography with electrochemical detection. We have tested six commercial columns used for the purification step. We chose a rapid and reliable method with a mixture of strong cation-exchange and strong anion-exchange groups bonded onto a silica column. This protocol has been validated with samples of plasma from normal subjects, healthy elderly people, renal failure patients and patients with pheochromocytoma.