Determination of Cadmium, Copper, Lead, and Silicon in Anti-Hair Loss Dietary Supplements That Contain Various Plant-Derived Silicon Sources

In this research, an accurate procedure was developed to determine Cd, Cu, Pb and Si in dietary supplements using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS). The operational parameters for the graphite furnace method were thoroughly investigated, including the influence of the chemical modifier along with the optimisation of pyrolysis and atomisation temperatures. The detection limits for Cd, Cu, Pb, and Si were 0.02 µg L−1, 0.35 µg L−1, 0.18 µg L −1 and 0.98 µg L −1, respectively. The accuracy of the method was validated using INCT-MP4-2 (Mixed Polish Herbs) as a certified reference material and complemented by standard addition tests. The determined elemental contents showed satisfactory agreement with both certified values and the spiked amounts, as confirmed by a t-test at 95% confidence level. The validated procedure was successfully applied to nine commercial dietary supplements representing three botanical silicon sources (bamboo, horsetail, and nettle). The analysis revealed a cadmium concentration in one horsetail-based sample (H1) that marginally exceeded the EU regulatory limit, as well as a substantial discrepancy between the declared and measured silicon content in another horsetail-based sample (H2), where the determined value was nearly eight times lower than stated by the manufacturer.