Abstract
The increased use of dietary supplements in today's society has been attributed to the general public's greater awareness of what constitutes a healthy diet. The elemental content (Ca, Cd, Cr, Co, Cu, Fe, Mg, Mn, Mo, Ni, Pb and Zn) of seventy-four dietary supplements (tablets, capsules and powders) was analysed by inductively coupled plasma mass spectrometry (ICP-MS). Different digestion methods (wet open vessel and microwave) were developed for the dissolution of dietary supplements, utilising both concentrated nitric acid and hydrogen peroxide. Both digestion procedures were found to give no significant statistical difference between the experimental results and certified values at a 99% confidence limit (Paired t-test) for all element values in two certified reference materials, namely NIES Rice Flour and IGGE Tea. For both certified reference materials, there was. The elemental content of the dietary supplements ranged from 0.1-200 mg/g for macro essential elements (Ca, Fe and Mg), 1-500 mug/g for trace essential elements (Cr, Co, Cu, Mn. Mo, Ni and Zn) and 0.4-10 mug/g for non-essential elements (Cd and Pb), all on a dry weight basis. Comparison of experimental results with commercial label values for dietary supplements showed: (1) calculated Ca and Mg concentrations were systematically lower than the label values; and (2) the experimental results for the other essential elements were in good agreement. The essential element contribution of base materials was investigated, though the results were inconclusive. Dietary supplements containing fat-soluble vitamins were analysed for retinol acetate, ergocalciferol (D2), cholecalciferol (D3), tocopherol (E), tocopherol acetate and phylloquinone (K1) using a modified simultaneous high performance liquid chromatography (HPLC) method. For each vitamin, a recovery of >90% was obtained with the use of a direct solvent extraction procedure. An in vitro study into the bioavailability of iron and zinc in yeast-based supplements was accomplished. This study provided results suggesting that iron supplements containing vitamin C were more bioavailable than yeast or tablet-based supplements that contained no vitamin C. Zinc bioavailability was observed to be greater in multi-component and yeast-based dietary supplements.