A study of dye¯surfactant interactions. Part 2. The effect of purity of a commercial cationic azo dye on dye¯surfactant complex formation.

The interactions between the cationic azo dye C.I. Basic Yellow 25 and the cationic surfactant cetylpyridinium chloride have been studied by potentiometry, UV/VIS spectrophotometry and 1H NMR. The effect of the purity of the commercial sample of the dye on the dye¯surfactant interactions has been investigated. The results show that the cetylpyridinium chloride forms a complex with one of the components of the commercial sample of the dye in aqueous solution. The concentration of this component is decreased by purification of the commercial dye sample. The results also indicate that there are no dye¯surfactant interactions in solutions of the cationic and nonionic components of the dye. According to this observation, we conclude that the surfactant cetylpyridinium chloride does not form a complex with the dye component in the commercial sample of C.I. Basic Yellow 25, and that the reduction of the free surfactant cation concentration in the solution causes reduction of the levelling action of the surfactant in the system involving the same charged dye and surfactant.