Determination of selenite and selenomethionine by HPLC-HG-high power N2-MIP-MS: a suitable coupling for selenium speciation

The coupled technique, high performance liquid chromatography (HPLC) continuous hydride generation [flow-cell, with sodium tetrahydroborate (0.3% in 0.2% NaOH) and hydrochloric acid (3 M)] high power nitrogen microwave induced plasma [1.3 kW; 2.45 GHz, with an Okamoto cavity in a surface-wave mode (rectangular waveguide; WRJ-2)] mass spectrometry (N2-MIP-MS) has been investigated for selenite and selenomethionine (Semet) determination. The high power N2-MIP-MS was successfully coupled with a HG system that is attached with a PRP-X100 anion exchange column. It was studied as an element specific detector for the optimization and determination of selenite and Semet using the major isotope of selenium (m/z 80). The adjusted HG system was very promising for the direct determination of the selenite and Semet without derivatization prior to HG. The N2-MIP was stable in coupling with the HG system. The separation was performed with a phosphate buffer (15 mM at pH 7.0), which showed minimum suppression of volatile hydride formation from Semet among the mobile phases examined. The recovery of Semet (98–104%), prepared in the phosphate mobile phase, was almost same as that of Semet prepared in Milli-Q water. The detection limits of selenous acid and Semet obtained with the optimized HPLC-HG-N2-MIP-MS system were 0.73 and 8.7 µg l−1, respectively. The repeatability (RSD for three successive analyses) achieved for selenous acid and Semet were within 2.3–5.2%. The combined HPLC-HG-N2-MIP-MS was applied to the determination of selenium compounds in human urine. The separation of selenite and Semet (spiked) in human urine was reasonable. The concentration of selenite found in the human urine was 3.7 ± 0.2 µg l−1 which agreed well with the HPLC-ICP-MS value (3.8 ± 0.2 µg l−1). Furthermore, in urine the retention times of selenite and Semet were shifted towards the solvent front. The spectroscopic interference due to calcium was removed.