Polarographische Bestimmung der Komplexbildungskonstanten der Schwermetallkomplexe der Nitrilotriessigsäure

Summary

An attempt to measure the equilibrium constant with regard to the complex formation of nitrilotriacetic acid (Schwarzenbach's complexone I) with some heavy metals has been carried out by means of the polarographic method. The metallic ions bound in the complex are deposited at a more negative potential than the free cations, so that two separate waves appear on the current-voltage curve. However, the heights of these waves are not proportional to the respective concentrations, because of the interference of kinetic factors that are involved in the reduction process. These factors were eliminated by using a streaming mercury electrode with which the following constants of complex formation have been found: logK_CdX=9.16,μ=0.1; logK_CdX=8.85,μ=0.2; logK_CdX=8.61,μ=0.3; logK_PbX=10.68,μ=0.2; logK_ZnX=10.35,μ=0.2;μ denotes the ionic strenghth of the solution.