Abstract: In this paper a new standard addition method is proposed, in which sample solutions with the same volumes V_x and different concentrations C_x/N(in general, 1≤N≤2) are separately titrated with the standard solution .The volume and concentration of the standard solution added to each sample are V_s and C_s/N, where Nis the same as that of the titrated sample solution.Based on this procedure semilogarithmic linear plots of △E_N vs.Nwere obtained, where △E_N is the difference between potential after addition and potential of the original sample, Nis the decreased times of concentrations of correlative sample and the standard solution.The con-centration C_x of the analyte is determined from the intersection, N⁰, by the equation:C_x＝C_sV_s[(N⁰-1)V_x+N⁰V_s].

Key words: Ion-selective electrode, Standard addition method, Concentrations of sample and standard series decreased at identical rates