**2. Materials and Methods**

### *2.1. Reagents and Analytical Standards*

Hydroxylammonium chloride (reagent grade >98% *w*/*w*), ammonium acetate (>99% *w*/*w*), (S,S)-ethylenediamine-*N*,*N*-disuccinic acid-trisodium salt solution (35% *v*/*v*), hydrogen peroxide solution (30% *v*/*v*), acetic acid (ACS reagen<sup>t</sup> >97% *v*/*v*), and nitric acid (ACS reagen<sup>t</sup> >67% *v*/*v*) from Sigma-Aldrich (Saint Louis, MI, USA) were used as reagents. Only ultra-pure water was used for analytical preparations and dilution. Atomic Absorption Spectrometer (AAS) standards were employed for Cd, Cr, Cu, Fe, Pb, Zn (Carlo Erba, Reagenti), Mn, and Ni (Fluka Reagents).
