Determination of some metallic ions by kinetic methods, based on a Landolttype redox system

A kinetic method is described for determining traces of Mo(VI), Cu(ll) add Fe(lll) alone or Mo(VI)-Cu(ll) and Mo(VI)-Fe(lll) in the presence of each o ther By using hydrogen peroxide-iodide reaction, which is catalyzed by Mo(V I) Cu(ll) and Fe(III), in the presence of thiosulphate or ascorbic acid as scavengers far iodine, to arrange a Landolt-type system, a clock method was used for rate measurements. Concentration as low as 4.10(-8) mol/L (about 40 mu g/L) of Mo(VI), 7.4.10( -7) mol/L (similar to 50 mu g/L) of Cu(ll) and 1.3. 10(-6) mol/L (similar t o 72 mu g/L) of Fe(III) could be detected. Calibration lines, with quite go od correlation coefficients, ha ve been Obtained by plotting the ratio of c atalyzed and uncatalyzed rates as a function of catalyst concentration. Cum ulative effects were noticed when two species were present in the mixture. The catalytic effect of Cu(ll) and/or Fe(lll) has been suppressed by adding EDTA to the solution, when only Mo(VI) has been measured.