Development of H+-Selective Electrode with a Cation Exchanger Membrane and Its Application to a Control Chemical Analysis of a Pickling Solution Containing Nitric and Hydrofluoric Acids

Abstract

A method concerning ion-selective electrodes was studied for the direct determination of a concentration of H⁺ or HF in a pickling solution of stainless steel containing HNO₃, HF, and metal ions. Strongly acidic cation exchanger membrane was the most suitable one as an electroactive substance for a H⁺-selective electrode to measure H+ concentration in a test solution. The interference of HF and cationic metal ions could be suppressed and lowered the general measuring error occur red in an ion-meter by diluting 50-100 times (in volume) a pickling solution with 0.05 N HNO3 solution. The concentration of H+ or HF in a test solution taken from a pickling solution was determined directly in terms of the following equations by measuring the potential between a H⁺-selective electrode and a reference electrode or a F--selective electrode:
E_H=E_H⁰+RT/F1n[H⁺] and E_HF=E_HF⁰+RT/F1n[HF]
The concentrations of H+ and HF in a pickling solution were determined from these values by using the calibration curves. By the present method, 0.1-2.0 mol/l of H⁺ and 0.9-3.2mol/l of HF in a pickling solution could be determined, and the standard deviations between these and those obtained by the conventional methods were 0.06 mol/l and O.05 mol/l for H+and HF, respectively, in the presence of 0-0.5 mol/l of Fe³⁺, 0-0.1 mol/lof Cr³⁺, and 00.08 mol/l of Ni²⁺. The present method is simple, needs no special reagent, and is useful for a control chemical analysis of pickling solutions containing HNO₃, HF, and metal ions.