Determination of the concentration of strong acids with a permaplex membrane electrode in the presence of hydrofluoric acid and various cations

A strongly acidic cation-exchanger membrane electrode was used to measure the concentration of nitric, hydrochloric and sulphuric acid over the range 10^-3-7 N. Hydrofluoric acid interfered when its concentration approached that of the strong acid. The electrode showed selectivity for H⁺ over the cations Cr³⁺, Fe³⁺, Ni²⁺ Ag⁺ and K⁺. Measurements of the acidity could be made with a reproducibility of the order of tenths of a millivolt. It was shown that the electrode could be used for direct measurement of acidity in stainless steel pickling baths.