Samples were digested in polytetrafluoroethylene (PTFE) vessels
using Ethos Plus Labstation (10-vessel capacity) or Ethos 1 Advanced
Microwave (24-vessel capacity) systems (Milestone Inc.,
USA). Elemental analyses were performed on Optima 7300 DV
ICP–OES and Elan DRC II ICP-MS instruments (Perkin–Elmer SCIEX,
USA), which used WinLab32 for ICP software version 4.0.0.0305 and Elan software version 3.4, respectively. Operating conditions
are detailed in Tables 1 and 2.