Recoveries of cyanide from different metal complexes were evaluated in the metal:cyanide stoichiometric ratios indicated in Table 4.
Complete recoveries were found from labile complexes formed with Cu(II), Cd(II), Ag(I) and Zn(II) and low values were achieved from Ni(II) (32%), and Co(II) (26%).
Stable and inert com-plexes (e.g. Fe(CN)64− and Fe(CN)6 3−) were not detected.
These results agreed with literature data [7], thus showing that the pro-posed procedure is an alternative for ADC determination.
The only discrepancy was observed for Hg(II) complexes (recoveriesof 72–78% and 100% in the proposed and reference procedures, respectively).
However, only trace amounts of this species areexpected in natural water samples.
If necessary, recovery of cyanide from mercury(II) complexes can be improved by addition of ligands which yield highly stable complexes, such as dithizone or tetraethylenepentamine [40].