Determination of hydrofluoric acid in inhibited red fuming nitric acid

Abstract

A simple method has been devised for directly measuring fluoride-ion concentrations in inhibited red fuming nitric acid, which is commonly used in propellents. The technique involves the use of a newly developed fluoride-sensitive electrode, and the concentrations are determined by measuring the potential developed between this electrode and a reference electrode. A special procedure, involving a buffer solution, was devised for weighing the inhibited nitric acid before neutralisation, dilution and measurement. The results are more accurate than those obtainable by the commonly used, and more complex, indirect methods. For the particular instance of inhibited red fuming nitric acid, the technique also proved superior to another proposed direct method in that it is effective with samples as small as 1 g.