The application of acid hydroxy or amino azo dyes containng sulfo or carboxy groups as reagents for the determination of tetra-n-butylammonium bromide as the model compound was compared. The sulfonated dyes are applicable within a broad range of pH 2–10 with the exception of amino azo dyes, the protonated form of which, formed at pH < 3, is precipitated from the solution. The application of carboxy azo dyes, owing to their high pKA values, is strongly limited to very high pH values. Methyl red is an exception, its pKA value is in the range of 4.88–5.06.

        Key words: extraction spectrophotometry – methyl red – sulfo azo dyes – carboxy azo dyes – tetra-n-butylammonium bromide