Quantitative measurement of plasma free metanephrines by ion-pairing solid phase extraction and liquid chromatography–tandem mass spectrometry with porous graphitic carbon column

Plasma free metanephrine and normetanephrine are the best biomarkers for diagnosing pheochromocytoma. In the past few years, liquid chromatography–tandem mass spectrometry has become the preferred technology to measure plasma metanephrine and normetanephrine because of its high sensitivity and specificity, as well as fast and simple sample preparation. In this study, we report a liquid chromatography–tandem mass spectrometry method for measuring plasma metanephrine and normetanephrine. A solid phase extraction method using ion-pairing reagent and C18 stationary phase was used for sample preparation. We tested a porous graphitic carbon column and a HILIC column for chromatographic separation, and the former one showed better resolution with no interference from plasma matrix. This method was linear from 7.2–486.8 pg/mL for metanephrine and 18.0–989.1 pg/mL for normetanephrine with an accuracy of 92.2–111.8% and 92.1–115.0%, respectively. Inter-assay and intra-assay CV for metanephrine and normetanephrine at two different concentration levels ranged from 2.0% to 10.9%. In conclusion, this liquid chromatography–tandem mass spectrometry method using ion-pairing solid phase extraction and porous graphitic column was simple and efficient for measuring plasma metanephrines.