Selenium speciation in enriched and natural samples by HPLC-ICP-MS and HPLC-ESI-MS with perfluorinated carboxylic acid ion-pairing agents

Selenium-enriched plants, such as hyperaccumulative phytoremediation plants (Astragalus praleongus, 517 mu g g(-1) Se, and Brassica juncea, 138 mu g g (-1) Se in dry sample), yeast (1200, 1922 and 2100, mu g g(-1) Se in dry sa mple), ramp (Allium tricoccum, 48, 77, 230, 252, 405 and 524 mu g g(-1) Se in dry sample), onion (Allium cepa, 96 and 140 mu g g(-1) Se in dry sample) and garlic (Allium sativum, 68, 112, 135, 296, 1355 mu g g(-1) Se in dry s ample) were analyzed by HPLC-ICP-MS for their selenium content and speciati on after hot water and enzymatic extractions. Reference samples with natura l selenium levels, such as onion and garlic controls, cooking garlic powder , baking yeast powder and a commercial garlic supplement were also analyzed . Selected samples were also examined by HPLC-electrospray ionization (ESI) -MS. HPLC was mostly carried out with 0.1% heptafluorobutanoic acid (HFBA) as ion-pairing agent in 1 + 99 v/v methanol-water solution, but 0.1% triflu oroacetic acid (TFA) in 1 + 99 v/v methanol-water solution was also utilize d to permit chromatography for compounds that did not elute with HFBA. More than 75% of the total eluting selenium compounds, based upon element speci fic detection, were identified from retention time data and standard spikin g experiments, and between 60 and 85% of compounds were identified by MS, w ith up to 25% of the total eluting molecular selenium species being unident ified as yet. Limits of quantification (LOQ, defined as the concentration g iving an S/N of 10) for HPLC-ICP-MS were in the range 2-50 ng mL(-1) Se in the injected extracts for the selenium-enriched samples and 2-10 ng mL(-1) Se for the natural selenium level samples. LOQ values for HPLC-ESI-MS were ca. 100 times higher than those measured by HPLC-ICP-MS.