Trace element and mercury speciation analysis in yerba mate (Ilex paraguariensis)

Background

Yerba mate, a popular beverage in South America, is rich in bioactive compounds and minerals. However, yerba mate leaves may contain toxic metals and environmental contaminants. This study performed multi-element analyses using ICP-MS and ICP OES and mercury speciation by GC-CV-AFS and CV–AAS to profile infusions of ten yerba mate samples consumed in Brazil and Uruguay.

Materials and methods

For ICP OES and ICP-MS analyses, 500 mg infusions of samples were prepared and diluted with 10 % v/v HNO₃. Ultrasonic-assisted extractions of mercurial species were made followed by distillation and dilution with water for CV-AAS. For GC-CV-AFS speciation, samples were extracted and distilled, using 200 μL aliquots for analysis.

Results

The most abundant elements in the digested solid samples were K, Ca, and Mg, whereas in infusions the ranges were up to 9.18 mg g⁻¹ for K, 0.68 mg g⁻¹ for Ca, and 2.74 mg g⁻¹ for Mg. Pb presented a mean concentration of 260 µg kg⁻¹ in leaves but it was not found in infusions. Hg²⁺ was found from 0.67 to 0.96 μg kg⁻¹ in leaves with one sample presenting 0.67 μg kg⁻¹ of CH₃Hg.

Conclusion

K, Ca, and Mg were the most abundant elements in the yerba mate samples. Four samples showed ultra-trace concentrations of Hg²⁺ and one of CH₃Hg.