Contribution to selenium speciation in cerebrospinal fluid samples

The well known beneficial health effects of Se have demanded the development of speciation methods for providing deeper insight into Se-metabolism and transport. This is also of significant importance for healthy brain function. Thus, Se-speciation was performed in 15 individual cerebrospinal fluid (CSF) samples (a′3 replicates) from neurologically healthy persons. First size exclusion chromatography (SEC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) equipped with a dynamic reaction cell (DRC) was used for monitoring the most abundant 80Se isotope. SEC separation provided Se-species characterization distinguishing between seleno-proteins and Se- low molecular mass (LMM) compounds. However, for improved speciation information a method based on strong anion exchange (SAX) separation was employed and optimized for CSF samples. The analysis of CSF samples from different individuals revealed six Se-species comprising relative mean concentrations of 8.5% (range: 5–11%), 27% (range: 20–31%), 2.2% (1.7–3.9%), 17% (range: 11–19%), 26% (range: 24–31%) and 20% (range: 19–21%) of the total Se amount, which in average was 3.6 μg L−1 (range: 2.9–4.8 μg L−1). Single and mixed Se-standard compounds were analyzed for verifying respective retention times, using serial UV- and ICP-MS detection. Additionally, standard additions were made to CSF samples for further peak identifications. By means of standard matching selenate, thioredoxinreductase (TrxR) and Se-albumin (Se-HSA) were found. No matches for Se methionine (SeM), Se-cystine (SeC), glutathioneperoxidase (GPx) and selenite were seen. Since no standard for selenoprotein P (SePP) was commercially available, this compound was prepared freshly from human serum using a Heparin-affinity column. It turned out that this SePP fraction showed matched retention time with the first peak in SAX separation, but also with selenate when age of the prepared standard was increasing.