Determination of selenium in biological samples using ICP-QMS

A method for the determination of selenium traces in plant tissue samples is described. Freeze-dried and homogenized biological samples mere decomposed with HNO3, HF and H2O2 by using closed-vessel microwave digestion under temperature and pressure control. NIST SRM 1577b Bovine Liver and NIST SRM 1547 Peach Leaves reference materials were investigated to optimize the analytical procedure. Selenium concentrations were measured with quadrupole-based inductively coupled plasma mass spectrometry (ICP-QMS) using external calibration and the isotope dilution method. A special solution introduction device combining pneumatic nebulization with hydride generation in the thin liquid film on the malls of the minicyclonic spray chamber was employed for sample introduction into the ICP-MS, which allowed the sensitivity for Se to be increased by up to one order of magnitude without increasing the memory effects. SRMs were doped with different amounts (0, 0.1, 0.2, 0.5 and 1.0 mug/g) of enriched Se-78 spike (98.58% of Se-78) before digestion to study the method performance and selenium losses during sample preparation. For a given matrix selenium losses were reproducible as follows: 9.9+/-1.6% for Bovine Liver SRM, 15.8+/-3.6% for Peach Leaves SRM and 20.0+/-4.5% for the real plant tissue samples. The detection limit for selenium calculated for solid plant tissue was 0.2 mug/g (3 sigma -criteria, m/z=82, digestion 1:1000) using conventional pneumatic nebulization for solution introduction and 0.03 mug/g for a combination of pneumatic nebulization with hydride generation. Applying the method developed, a large number of plant tissue samples were analyzed to study selenium behavior and accumulation in the environment.