An Indirect Potentiometric Determination of Multivalent Ions Using Chelate Formation

Abstract

A simple potentiometric determination of multivalent ions for which no suitable ion-selective electrodes are available is proposed.
When a sample solution containing an analyte ion(N) is added to the ML-chelate solution in which a M-selective electrode is immersed, where M and L denote a metal ion and chelateforming ligand respectively, M is released by displacement reaction. N is determined by use of the calibration curve, i. e., the electrode potential vs. the negative logarithm of analyte concentration (pcx) plots. According to the theoretical considerations on the linearity of the calibration curve, the lower limit of the linear range decreases as IC(ML) increases and the upper limit increases as the ratio of K'(NL)/Kl(ML) or the initial concentration of ML increases, where K' is a conditional stability constant. By using Cu-edta and a Cu(II)-selective solid-state electrode, the linear calibration curves were obtained in the pc z range 3.00-5.30for Fe(III), 3.30-5.26 for Bi(II), and 2.94-4.80 for Cr(III).