An automated magnetic bead extraction method for measuring plasma metanephrines and 3‑methoxytyramine using liquid chromatography tandem mass spectrometry
Liquid chromatography tandem mass spectrometry (LC-MS/MS) is used routinely in clinical diagnostics； however, automating the sample pretreatment is challenging. We established and evaluated an automated method based on the magnetic bead extraction principle (MBE) to measure normetanephrine (NMN), metanephrine (MN), and 3-methoxytyramine (3-MT).
The target analytes were extracted, purifed, and concentrated using diferent solvents and chemical bond–modifed magnetic beads transferred via a magnetic bar. The linearity, recovery, matrix efect, and precision of MBE were evaluated thoroughly, and compared with traditional solid-phase extraction (SPE) using 131 plasma samples. The chromatography peaks of metanephrines and 3-MT, extracted via MBE, are symmetrical, without interfering peaks. The linearity was excellent with correlation coefcient (r) > 0.99. The MBE exhibited good reproducibility with within-run coefcient variations (CVs) of 1.96–2.00%, 4.06–5.75%, and 3.89–4.90% for MN, NMN, and 3-MT, respectively. The total CVs for MN, NMN,and 3-MT were 1.96–2.80%, 5.12–5.75%, and 5.44–6.27%, respectively. The relative recoveries for MN, NMN, and 3-MT varied between 93.5 and 107.4%, whereas their biases were all within 10%. The results for MN, NMN, and 3-MT extracted via MBE compared with SPE exhibited excellent correlation, with r > 0.99； the mean bias% for MN, NMN, and 3-MT were small (−2.9%, −3.2%, and −3.2%, respectively). In conclusion, the automated MBE method for measuring plasma metanephrines and 3-MT can be applied in future routine clinical diagnostics, and the MBE principle may indicate a new era for LC-MS/MS in clinical application.