Determination of Total Selenium and Extractability of Selenium in Commercially-Available Dietary Supplements by Inductively Coupled Plasma - Mass Spectrometry (ICP-MS)
Upper limits for the supplementation of micronutrients are still undecided in many European countries. These limits are of particular interest for selenium because of the narrow range of acceptable intake. Standard analytical protocols to check for compliance must be consistent for a variety of dietary supplements. Emerging products in the evolving market for dietary supplements and over-the-counter (OTC)-medications must be factored in as well. The ICP-MS determination of selenium is well established for scientific research, but a systematic comparison of the operation modes for a realistic set of samples is still missing. In this manuscript, five common cell-techniques for interference removal were approved by a certified reference material (CRM) and applied to a variety of 28 different dietary supplements after microwave digestion. The comparison reveals these operation modes are less consistent for some supplements than for the CRM, whereas 78Se in collision mode was identified as being the most robust. The results for the supplements varied within tolerable limits from the labeled dosage. Extraction with TRIS-buffer was employed as a minimally invasive method to determine the impact in comparison to the total selenium quantification, showing variation among the labeled species (selenomethionine (∼100%), methyl-seleno-cysteine (94%), selenite and selenate (60–100%), selenized yeast (11–28%), spirulina algae (70%)).
