An approach to the identification of unknown signals in selenium speciation analysis of yeast by reversed-phase chromatography with ICP-MS detection is described. The analytical strategy was based on: (i), heart-cutting of a Secontaining fraction in the reversed-phase chromatographic eluate followed by its lyophilization; (ii), pneumaticallyassisted electrospray (ESI) MS and ESI tandem MS of the lyophilizate; and (iii) confirmation of the fragmentation pattern obtained using the sulfur analogue of the seleno compound that was expected to have been identified. The approach developed allowed the identification of Seadenosylhomocysteine as the major selenium species in an extract of a selenized yeast sample.

A novel analytical approach based on a combination of multidimensional hyphenated techniques and cloning of the Ni-resistance gene using yeast complementation screens was developed for the identification of nickel species in a Thlaspi caerulescens hyperaccumulating plant. The presence of an unknown strong Ni complex was demonstrated by size exclusion HPLC-capillary electrophoresis with ICPMS detection. The Ni-containing peak was characterized by electrospray MS (m/z 360) and shown by collision-induced dissociation MS to be a chelate with a tricarboxylic amino acid ligand. To identify the species and demonstrate its functional character, a cDNA library was constructed from T. caerulescens, expressed in the yeast, and screened on a toxic Ni2+ medium. The extract from the surviving transformant culture gave identical HPLC-ICPMS, CZE-ICPMS, and ES MS/MS data and contained a cDNA insert homologous to the nicotianamine synthase gene. This observation allowed the identification of nicotianamine as the nickel-binding ligand. The presence of the Ni-nicotianamine complex was ultimately demonstrated by comparing tandem mass spectra of the plant and yeast extracts with those of a synthetic standard.

Two experiments were conducted on broiler chickens to compare the effect of a new organic Se source, 2-hydroxy-4-methylselenobutanoic acid (HMSeBA; SO), with two practical Se additives, sodium selenite (SS) and Se yeast (SY). The relative bioavailability of the different Se sources was compared on muscle ( pectoralis major) total Se, selenomethionine (SeMet) and selenocysteine (SeCys) concentrations and apparent digestibility of total Se (AD Se ). In the first experiment, from day (d) 0 to d21, Se sources were tested at different supplied levels and compared with an unsupplemented diet (NC). No significant effects were observed on growth performance during the experimental period. However, the different Se sources and levels improved muscle Se concentration compared with the NC, with a significant source effect in the following order: SS , SY , SO (P,0·05). Seleno-amino acids speciation results for NC, SY and SO at 0·3 mg Se/kg feed indicated that muscle Se was only present as SeMet or SeCys, showing a full conversion of Se by the bird. The second experiment (d0 -d24) compared SS, SY or SO at 0·3 mg Se/kg feed. The AD Se measurements carried out between d20 and d23 were 24, 46 and 49 % for SS, SY and SO, respectively, with significant differences between the organic and mineral Se sources (P,0·05). These results confirmed the higher bioavailability of organic Se sources compared with the mineral source and demonstrated a significantly better efficiency of HMSeBA compared with SY for muscle Se enrichment.