Selenium speciation analysis of selenium-enriched supplements by HPLC with ultrasonic nebulisation ICP-MS and electrospray MSMS detection

Size-exclusion, anion-exchange and reversed-phase ion-pair RP-IP HPLC were used in combination with ICP-QMS for selenium Se-specific detection and quantitation of Se-compounds in extracts of Se-yeast and Se-methylselenocysteine SeMC based supplements. On-line electrospray ionisation ESI-MSMS combined with RP-IP HPLC allowed characterisation of such materials in terms of species identification. Accelerated solvent extraction ASE was evaluated for extraction of the Se-compounds from the complex matrices in water. Alternatively, digestion with proteolytic enzymes was used for yeast protein hydrolysis. The use of ultrasonic nebulisation in combination with HPLC-ICP-QMS for Se speciation led to detection limits up to six-fold lower as low as ng l−1levels than those obtained with pneumatic nebulisation. Such enhancement of the ICP-MS capabilities for Se detection, combined with an improved separation using the newly developed RP-IP-HPLC method, allowed quantification of minor Se species such as SeMC in yeast extracts. Identification of the main compounds in yeast and SeleniumMC™ tablet hydrolysates as SeMet and SeMC, respectively, was accomplished by on-line RP-IP HPLC with ESI-MSMS. Identification of SeMC in yeast digests, on the basis of retention time, molecular mass determination for the M H 80Se ions mz184 and detection of its product ions, is reported here for the first time. The mass spectral confirmation for SeMC in yeast is of interest, as this species is believed to be metabolised in animals and humans to methylselenol CH3SeH, an anti-carcinogenic Se-metabolite.