Evaluation of on-line coupling size exclusion chromatography electrothermal atomic absorption spectrometry for selenium speciation

Chromatographic effluents were on-line analyzed by Zeeman-ETAAS, using a flow-through cell placed in a graphite furnace autosampler as interface. To obtain high sampling rates, the use of fast graphite furnace programmes was studied. Conventional programmes of 96 s were reduced to 18 s by using hot injection (120 degrees C) and reducing the charring step to 2 s. The increase of the injection volume from 20 to 60 mu l lengthened the programme to 46 s. Nickel had to be added to get a comparable response for both inorganic and organic selenium species (selenite and selenomethionine) and to reduce the interferent effect produced in presence of the chromatographic eluent (TRIS 0.01 mol l(-1) NH4NO3 0.1 mol l(-1), pH 7). The optimized conditions were applied to the speciation of selenium in human erythrocyte lysates by size exclusion LC-ETAAS. Using a high performance size exclusion column selenium could be assigned to proteins of 100 and 35 kDa. Detection limits in the range of 1 ng (2 mu g l(-1) for 500 mu l injection volume) were obtained for the combined technique.