Determination of selenium in dietary supplements by ETAAS and HG-AAS: A comparative study

A study was carried out to establish a reliable procedure for determining Se in dietary supplements. Three different brands of Se food supplements were evaluated. These supplements were digested with HNO 3 and H 2 O 2 using a two-cycle microwave procedure. Electrothermal atomic absorption spectrometry (ETAAS) and hydride generation-atomic absorption spectrometry (HG-AAS) techniques were selected for total Se determination. The adverse effects of potentially interfering metals that are normally present in these products were taken into account. In particular, the effect of Cu, Mn, and Zn on the Se signal was investigated. Copper reduces the Se signal significantly when HG-AAS was used for quantification. On the other hand, no interference effects were detected when ETAAS was used and for this reason it was selected as the best alternative to analyze the samples. The overall approach was tested in tablets of vitamins-minerals-amino acids, nutritional supplements and Se-enriched yeast. The selenium content ranged from 15.9±0.7 to 81.1±3.3 μg of Se per tablet. The data obtained demonstrate that the Se content reported on the labels of dietary supplements are often inaccurate. The detection limits were found to be 0.18 pg g -1 Se and 0.06 pg g -1 Se for ETAAS and HG-AAS, respectively. Precision was always better than 6%, while the recovery data ranged between 93 and 105%.