Study of interaction between a cationic surfactant and two anionic azo dyes by ion-selective electrode technique and spectrophotometry

Interaction between a cationic surfactant, hexadecyltrimethylammonium bromide (HTAB), and two anionic azo dyes, C.I. Direct Orange 26 (DO26) and Direct Red 16 (DR16) has been investigated using surfactant-selective electrode and spectrophotometry techniques. In ion-selective electrode technique an HTAB surfactant-selective membrane electrode has been used. The electromotive force versus total surfactant concentration has been plotted for the systems of HTAB/DR16 and HTAB/DO26 in 1 × 10−4 and 1 × 10−3 mol dm−3 NaBr at 25 °C. The concentrations of free and bound surfactant and also dye–surfactant complex constant, K, could be obtained from the experimental data. The data show that significant binding takes place and the critical concentration associated with the saturation of the dyes with bound surfactant has been determined. The results also indicate that in the DO26/HTAB system, where more hydrophobic dye DO26 is used, the dye–surfactant interaction is stronger than in DR16/HTAB system, which shows the importance of hydrophobic forces in the interaction.