ORIGINAL PAPER Selenium speciation in paired serum and cerebrospinal fluid samples Nikolay Solovyev & Achim Berthele & Bernhard Michalke Received: 21 May 2012 / Revised: 18 July 2012 / Accepted: 20 July 2012 / Published online: 7 August 2012 # Springer-Verlag 2012 Abstract Se speciation was performed in 24 individual paired serum and cerebrospinal fluid (CSF) samples from neurologically healthy persons. Strong anion exchange (SAX) separation, coupled to inductively coupled plasma– dynamic reaction cell–mass spectrometry (ICP-DRC-MS), was employed. Species identification was done by standard matched retention time, standard addition and by size ex- clusion chromatography followed from SAX (2-D SEC- SAX-ICP-DRC-MS) and by SAX followed from CE-ICP- DRC-MS (2-D SAX-CE-ICP-DRC-MS). Limit of detection (LoD, 3×standard deviation (SD) of noise) was in the range of 0.026–0.031 μg/L for all investigated species and thus was set uniformly to 0.032 μg/L. Quality control for total Se determination was performed by analysing control materials “human serum” and “urine”, where determined values met target values. Several Se species were found in both sample types having following median values (sequence: serum/ CSF, each in μg Se/L): total Se, 58.39/0.86; selenoprotein P (SePP), 5.19/0.47; Se-methionine (SeM), 0.23/<LoD; glu- tathione peroxidase (GPx), 4.2/0.036; thioredoxinreductase (TrxR), 1.64/0.035; Se IV, 12.25/0.046; Se-human serum albumin (Se-HSA), 18.03/0.068. Other Se species, such as Se-cystine (SeC), Se VI and up to four non-identified com- pounds were monitored (if ever) only in very few samples usually close to LoD. Therefore, their median values were <LoD. Linear relationships based on median values provide information about Se-species passage across neural barriers (NB): SePP -serum is significantly correlated to total Se -serum when the latter was >65 μg/L; however, SePP -CSF appeared independent of SePP -serum . For Se-HSA -serum versus (vs.) Se-HSA -CSF , a weak linear relationship was found (r 2 0 0.1722). On the contrary, for anti-oxidative Se-enzymes, higher r 2 values were calculated: GPx -serum vs. GPx -CSF , r 2 0 0.3837; TrxR -serum vs. TrxR -CSF , r 2 0 0.6293. Q -Se-species values (0 ratios of CSF -Se-species /serum -Se-species ) were com- pared with the Q -Alb value (HSA -CSF /HSA -serum 0 clinical index of NB integrity) for deeper information about NB passage of Se species. The Q -Se-HSA value (3.8×10 -3 ) was in accordance to the molecular mass dependent restriction at NB (Q -Alb at 5.25×10 -3 ). Increased Q values were seen for TrxR (21.3×10 -3 ) and GPx (8.3×10 -3 ) which are not (completely) explained by molecular size. For these two anti-oxidative Se-enzymes (GPx, TrxR), we hypothesize that there might be either a facilitated diffusion across NB or they might be additionally synthesized in the brain. Keywords Selenium speciation . Cerebrospinal fluid . Serum . Thioredoxin reductase . Glutathione peroxidase Introduction Selenium is an essential trace element for humans. Its ben- eficial role for human health is generally accepted and includes protection against oxidative stress, prevention of heart diseases and cancer or optimal immune responses Published in the topical collection Metallomics with guest editors Uwe Karst and Michael Sperling. N. Solovyev Institute of Toxicology, FMBA, St. Petersburg 192019, Russia A. Berthele Department of Neurology, Klinikum rechts der Isar, Technische Universität München, 81675 Munich, Germany B. Michalke (*) Research Unit Analytical BioGeoChemistry, Helmholtz Center Munich—German Research Center for Environmental Health, Ingolstädter Landstr. 1, 85764 Neuherberg, Germany e-mail: bernhard.michalke@helmholtz-muenchen.de Anal Bioanal Chem (2013) 405:1875–1884 DOI 10.1007/s00216-012-6294-y