A rapid absorptiometric method for the determination of formates in corrosion products arising from paints, lacquers and woods

Abstract

A method has been evolved in which formate ions reduce an excess of silver nitrate to silver under slightly acidic buffered solution conditions. The method is applicable directly to cadmium and zinc corrosion products. Samples of corrosion products from ferrous metals require preliminary separation by distillation from phosphoric acid. The method is also applicable to the study of formic acid vapours evolved from paints, lacquers and woods, the acidic vapour being absorbed in a dilute aqueous solution of an alkali hydroxide. Allowance is made for the presence of residual metallic particles and for chloride interference.

A series of control standards is run concurrently with each batch of samples to compensate for daily changes in sensitivity because of the ageing of the colloid stabiliser. Recovery of formic acid from synthetic mixtures, based on a sample weight of 0·1 g, has been found to be ±4 per cent. for aqueous solutions and zinc products and ±6 per cent. for cadmium products, with a 95 per cent. confidence limit.