Quantification of selenium-tagged proteins in human plasma using species-unspecific isotope dilution ICP-DRC-qMS coupled on-line with anion exchange chromatography

Inductively coupled plasma dynamic reaction cell-quadrupole mass spectrometry (ICP-DRC-qMS) coupled on-line with anion exchange chromatography (AEC) has been developed for the quantification of selenium-tagged proteins in human plasma. Methane was employed as a reaction gas in the dynamic reaction cell to achieve the determination of (80)Se free of spectroscopic interference from (40)Ar(2)(+) and (79)BrH(+). Five selenium species including selenoprotein P (SelP), glutathione peroxidase (GPx), selenoalbumin (SeAlb), and two unknown selenospecies (U1 and U2) in a pooled plasma sample from five healthy people were separated using AEC, and the distribution of selenium in SelP, GPx, SeAlb, U1 and U2 (about 45.5%, 19.1%, 15.1%, 2.9% and 8.1%) was determined by ICP-DRC-qMS using species-unspecific isotope dilution ((80)Se/(77)Se). Based on the detection limit (DL) of selenium (0.54 ng mL(-1)), we estimated that the DLs for SelP and GPx were 0.59 pmol mL(-1) and 1.7 pmol mL(-1), respectively. Through the stoichiometry of the selenium atom in the selenium-tagged proteins, SelP (2.7 +/- 0.1 mu g mL(-1)) and GPx (5.4 +/- 0.2 mu g mL(-1)) were successfully quantified.