[Colorimetric method for the quantitative determination of arsanilic acid in combined medicated premixes].

A colorimetric method was worked out to determine negligible amounts of arsanilic acid, based on the property of amino groups to form a yellow stained Schiff base in the interaction with an acid solution of p-dimethyl- aminobenzaldehyde. The optic density of the coloured solution in methanol is determined at 450 nm. The presence of the A, D3, C, K3 vitamins, furazolidon, neomycin sulphate, and tylosine phosphate does not interfere with the determination of arsanilic acid.