Chemical composition (ICP-MS)

Inductively coupled plasma mass spectrometry (ICP-MS) Samples S1-S10 were analysed at the University of Warsaw Biological and Chemical Research Centre to determine their elemental composition. They were weighed and treated with an appropriate mixture of acids (4.0 mL 65% HNO3, Merck Suprapur®, 0.5 mL 40% HF, Merck Suprapur®). Next, the samples were digested in a closed microwave system (Milestone Ethos Up, 25 min ramping to 230°C, 15 min hold at 230°C). The resulting solutions were diluted by weight to about 50 g and subjected to elemental analysis. All solutions were measured by ICP MS (Perkin Elmer NexION300D). External calibration (Merck ICP Standard VIII, Merck Sn, Sb and Ti monoelemental ICP standards) with internal standard (Rh) correction was used. The accuracy of the calibration has been verified using reference materials SPS SW1 and SPS SW2 (Spectrapure Standards, Norway).