Determination of hydrofluoric acid in strong acid solutions such as stainless steel pickling baths with a lanthanum fluoride electrode and a permaplex membrane electrode

It is shown that the total amount of hydrofluoric acid in strong hydrochloric or nitric acid solutions with varying acidity can be determined directly with two ion-selective electrodes. Equations were derived and calibration procedures for both electrodes were developed. The influence of liquid junctions at the reference electrodes was investigated and it was possible to simplify the equations by the use of a suitable bridge solution. The formation constant of the dimer (HF)₂ was redetermined and found to be 0.26.