Standard Addition Potentiometry not Requiring Adjustment of an Ionic Strength of Sample

Abstract

A standard addition method with an ion-selective electrode which does not require the adjustment of the ionic strength of a sample is proposed.
After the sample, of volume V, is titrated with the first standard solution containing the analyte ion of a known concentration (c_S1), the sample solution of a certain volume V⁰ is added. Subsequently it is titrated with the second standard solution of a known concentration (c_S2) having the same ionic strength as that of the first standard solution.
If the electromotive forces, E₁ and E₂, which correspond to the titration volumes, vsi and vs2, by the first and second standard solutions that satisfy a condition of υ_S2 =υ_S1( V+ V⁰) / V-υ_S1⁰ are read off respectively on the two titration curves, the concentration, c_x of the analyte ion is determined from the slope of a linear plot of y vs. x (vυ_S1⁰ is the final volume of the first standard solution added):
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Concentrations of th e fluoride ranging from 10^-3 to 5×10^-5 mol⋅dm^-3 in the samples of various ionic strengths were determined with an error of less than 0.4% and a relative standard deviation of less than 0.5%.