POTENTIOMETRIC FLOW-INJECTION DETERMINATION OF MERCURY IONS USING DIANTIPYRILPROPYLMETHAN BASED ELECTRODE

Abstract

The possibility of using diantipyrylpropylmethane (DAPPM) as an electrode-active membrane component of the mercury-selective electrode (Hg-SE) is shown. To clarify the mechanism of membrane functioning we studied the equilibrium in the “membrane-solution” system as a function of the medium acidity and amount of the ionophore. The potentiometric selectivity coefficients of Hg-SE are determined with respect to some anions and cations by the method of bionic potentials. DAPPM at pH 0 - 1.5 is in the cation form, and mercury ions in 0.1 M HCl — in the form of a trichloromercurium ion. The ion associate DAPPM + [HgCl3]-formed under these conditions is the most stable at pH 1 and pCl 1, and the membrane responds only to trichloromercurate ions.. A mercury-selective electrode with an optimized membrane composition (in wt. %) contains: PVC — 32.32; o-NPOE — 64.63; DAPPM — 3.05 (DAPPM concentration 100 mM). The electrochemical characteristics are determined: the linear range (1 x 10-4- 1 x 10-2M) and slope of the electrode function (50 mV/dec). The operating range (pH 0 - 1.5), detection limit (6.3 x 10-5M), and the response time (15 - 20 sec) are determined. For optimal operation of the flow-injection system, a selection of the carrier stream has been made, which affects the stability of the line, the sensitivity and the performance of the analysis. The proposed electrode is used as a detector in the flow-injection determination of mercury in sewage water and “Achromin” cream. Optimum operation conditions of the flow-injection system which ensure the stability of the baseline, as well as the maximum sensitivity and performance of the analysis, are found. The correctness of the results of the determination of mercury is confirmed in spike tests.