Total Selenium Content of Commercial Food Supplements: Label Accuracy Evaluation

The determination of selenium in food supplements is of major interest due to the low range between beneficial and toxic effects of this element. The total selenium content of eight commercially available food supplements were determined and compared with the labeled values. Microwave-assisted acid digestion was used for sample mineralization and the selenium was determined by high-resolution continuum source atomic absorption spectrometry with electrothermal atomization (HR-CS ETAAS) after optimization of the electro thermal behavior of selenium in the presence of different chemical modifiers, and of pyrolysis and atomization temperatures. Palladium nitrate-magnesium nitrate was selected as matrix modifier and 1050 °C and 2000 °C were the optimum pyrolysis and atomization temperatures, respectively. The LOD and LOQ were of 0.10 and 0.34 μg g-1, respectively. A 3.2 % of intra-day precision was obtained, and inter-day precision RSD did not exceeded 6.7 %. The accuracy of the method was checked with a certified reference material and showed a good agreement between the obtained results and certified selenium content (p > 0.05). The determined total selenium content of the food supplements varied between 15.4 ± 0.9 and 205.3 ± 9.9 μg/ unit, with a difference from the stated amount ranging from -12% to +14%. Also, all supplements were in compliance with the recent recommendations made by the European Community regarding the acceptable difference between labeled and measured values for minerals and vitamins in food supplements, fixed in -20% to +45% of the declared on label.