Electrochemical investigations of the effect of N-substituted aminosulfonic acids with a piperazinic ring pH buffers on heavy metal processes which may have implications on speciation studies

The influence of piperazine-N,N'-bis(2-ethanesulfonic acid) (PIPES), N-2-hy droxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) and N-hydroxyethylpip erazine-N'-2-hydroxypropanesulfonic acid (HEPPSO) on the redox processes of cadmium, lead and zinc was investigated by differential pulse anodic strip ping voltammetry (DPASV) and differential pulse polarography (DPP) (only fo r lead). The studies showed that these pH buffers did neither complex cadmi um and zinc nor modify to a significant extent the reversibility of the hea vy metals electrochemical DPASV and DPP responses, under the experimental c onditions used, indicating that the three buffers might be suitable for spe ciation studies of those metal ions. Depression of lead peak current, recor ded by DPASV and DPP, in the presence of all the pH buffers was observed du e to surface coverage of the electrode by those compounds, which was confir med by alternating current voltammetry (ACV). A slight complexation was als o verified for lead-PIPES and lead-HEPES systems, this phenomenon being mor e marked for lead-HEPPSO system (log beta Pb-HEPPSO=2.56+/-0.06 (n=5), dete rmined by potentiometric titrations (pH measurements)). These results indic ate that these pH buffers are not suitable for lead speciation studies, unl ess the extent of its complexation by the buffer is considered. (C) 2000 El sevier Science B.V. All rights reserved.