Traceselect 9.8 m h2o2

Ultrapure water (resistivity ≥18.2 MΩ cm) was obtained from a Milli-Q Element water purification system (Millipore, Guyancourt, France). Trace metal analysis grade 14 M HNO₃ and 12 M HCl were acquired from PrimarPlus (Fisher Chemicals, Loughborough, UK), and a Savillex DST-4000 acid purification system (Savillex Corporation, Minnetonka, MN, USA) was used for further purification. TraceSELECT^® 9.8 M H₂O₂ was acquired from Sigma-Aldrich (Overijse, Belgium). Isotopic reference material NIST SRM 976 (National Institute of Standards and Technology—NIST, Gaithersburg, MD, USA) was used as an external standard in the Cu isotope ratio measurements. Ga and Cu single-element standard stock solutions (Inorganic Ventures, Nieuwegein, The Netherlands) were used as admixed internal standard and in-house standard solution for quality control of the isotope ratio measurements, respectively. Sample preparation was performed in a class-10 clean lab (PicoTrace, Göttingen, Germany).

Trace metal analysis grade 14 M HNO₃ and 12 M HCl acquired from PrimarPlus (Fisher Chemicals, UK) were further purified via sub-boiling distillation in a Savillex® DST-4000 acid purification system (Savillex Corporation, United States). TraceSELECT® 9.8 M H₂O₂ was acquired from Sigma-Aldrich (Belgium). Ultrapure water with a resistivity ≥18.2 MΩ cm was obtained from a Milli-Q Element water purification system (Millipore, France) and will further be referred to as MQ-water. The isotopic reference materials used for the isotope ratio measurements were NIST SRM 976 for Cu (National Institute of Standards and Technology–NIST, United States) and IRMM-014 for Fe (Institute for Reference Materials and Measurements–IRMM, Belgium). Adequate dilutions and mixtures of 1 g.L⁻¹ single-element standard stock solutions of Cu, Fe, Ni and Ga (Inorganic Ventures, the Netherlands) were used for quantification, mass bias correction (Ni and Ga as admixed internal standards), and for checking the quality of the isotope ratio measurements (Cu and Fe in-house standards). Sample preparation was performed in a class-10 clean lab (PicoTrace, Germany).