BIDIRECTIONAL ISOTACHOPHORETIC SEPARATION OF METAL-CATIONS USING EDTAAS A CHELATING AGENT

An operational electrolyte system using EDTA as a chelating agent was developed for the bidirectional isotachophoresis (ITP) of metal ions. The anolyte used was 20 mM HCl buffered by adding beta-alanine at pH 3 .6. The catholyte was 20 mM ammonia solution buffered by acetic acid a t pH 4.8 and containing EDTA in the range 0-1 mM. In relation to the c oncentration of EDTA, the isotachophoretic separation behaviour of eig hteen metal cations containing equimolar EDTA was studied by using wit h particle-induced X-ray emission (PIXE). They were Na+, Li+, Ba2+, Sr 2+, Mg2+, Ca2+, Mn2+, La3+, Ce3+, Co2+, Zn2+, Gd3+, Pb2+, Y3+, Ni2+, C u2+, Lu3+ and Fe3+ in increasing order of chelate stability constants. When a catholyte containing 0.1 mM EDTA was used, Na+, Li+ Ba2+, Sr2, Mg2+, Ca2+ and Mn2+ were completely recovered as cations and La3+, C e3+, Co2+, Zn2+, Gd3+, Pb2+, Y3+, Ni2+, Cu2+ and Lu3+ were completely recovered as chelate anions. The recovery was incomplete for a test mi xture without adding EDTA, even when the EDTA concentration in the cat holyte was 1 mM. Absolute mobilities of several chelates were obtained and the concentration and pH of isotachophoretic zones were simulated to clarify the decomposition during migration.