Speciation and identification of organoselenium metabolites in human urine using inductively coupled plasma mass spectrometry and tandem mass spectrometry

A method for speciation and identification of organoselenium metabolites found in human urine samples using high performance liquid chromatograph/inductively coupled plasma mass spectrometry (HPLC/ICP-MS) and tandem mass spectrometry (MS/MS) is described. Reversed-phase chromatographic separation was used for sample fractionation with the ICP-MS functioning as an element-selective detector, and six distinct selenium-containing species were detected in a human urine sample. Fractions were then collected and analyzed using a triple quadrupole mass spectrometer with electrospray ionization and collision-induced dissociation to obtain structural information. The first two fractions were identified specifically as selenomethionine and selenocystamine, estimated to be present at approximately 11 and 40 ppb, respectively. To the best of our knowledge, this is the first time these two metabolites have been positively identified in human urine.