The digestion medium consisted of 5 ml 70% ultrapure HNO3 (J.T. Baker Instra-Analyzed Reagent, NJ, USA) and 5 ml 15% H2O2 (30% ExtraPure, Riedel de Häen, Selze, Germany).
Thedigestion medium consisted of 5 ml 70% ultrapure HNO3 (J.T. BakerInstra-Analyzed Reagent, NJ, USA) and 5 ml 15% H2O2 (30% ExtraPure, Riedel de Häen, Selze, Germany).