Separation of selenium compounds by CE-ICP-MS in dynamically coated capillaries applied to selenized yeast samples

Abstract

The selenium species in nutritional supplement tablets, based on selenized yeast, were separated by capillary zone electrophoresis using capillaries coated dynamically with poly(vinyl sulfonate) and detected by ICP-MS. Sample pre-treatment consisted of cold-water extraction by sonication and subsequent incubation of the cold-water extract with 6 M hydrochloric acid at 110 °C. The total selenium concentration in the cold-water extract was 3.5 mg L⁻¹ and corresponded to 9% of the total selenium content of the tablets. More than 20 different selenium compounds were separated in the cold-water extract within 13 min. The efficiency of the system corresponded to 620000 theoretical plates. When spiking the sample with available standards, co-migration was observed with selenomethionine and selenocystine–Se-methylselenocysteine—the latter species were not separated. When the cold-water extract was hydrolysed in hot hydrochloric acid, 45% of the selenium migrated within a single peak that co-migrated with selenomethionine. Other peaks co-migrated with trimethylselenonium, Se-methylselenomethionine, and selenocystine–Se-methylselenocysteine, respectively. The precision for the analysis of the aqueous extracts expressed as relative standard deviation (n = 3) on peak heights and areas was in the range 1.4–5.3%. Detection limits were better than 15 µg L⁻¹, corresponding to absolute detection limits less than 250 fg.