The factors which influence the abrupt change of indicator reaction rate in catalytic titration of metal ions with EDTA were investigated. The slope of the abrupt part in the titration curve, tan q, could be used to characterize the rate of indicator reaction. The effect of pH, amount of Cu-EDTA and Ni-Trien (N,N'-bis(2-aminoethyl)ethylenediamine) and of titration rate on tan q were studied experimental The approx. equation of tan q, which is a linear function of the initial concentration of Ni-Trien, the rate of EDTA added, and the rate constant of the reaction of EDTA and Ni-Trien was derived theor. Experimental result could be explained satisfactorily by this equation.

Key words: EDTA, IONS, METAL, REACTION RATE CONSTANT, MUTATIONS, CATALYTIC TITRATION