Spectrophotometric investigation of surfactants mediated aqueous solubilization of Nile blue

Abstract

In the current study, the solubilization of partially soluble Nile blue (NB) dye in an aqueous medium has been investigated. The solubilization was monitored using UV–Vis spectroscopic method by varying time intervals. The seven surfactants belong to different classes (cationic, anionic, non-ionic, and bio surfactant) were tested to examine their effects on the solubilization of Nile blue. The spectrum of NB in the presence of 10% methanol and varying concentrations of sodium dodecyl sulphate (SDS) showed the maximum absorbance among the tested solvents and surfactants. The spectra in anionic surfactant (SDS) closely resembled the spectra in methanol, a polar solvent. Whereas, in the cationic surfactants (CTAB and NDPC) it resembled with the spectra in chloroform, a non-polar solvent. The solubility of the NB was also examined by varying pH and introducing 0.2 to 1.0 M sodium chloride and potassium chloride salts in the NB solution at critical micelles concentration (cmc) of the selected surfactants. The solubility of NB was decreased with the increasing concentration of the salts irrespective of the surfactant nature due to the electronic shielding of ions, furnished by the salts. The solubilization was found to be maximum in the presence of sodium dodecyl sulphate (SDS) and about one half to the solubility in the methanol, while minimum with N-dodecyl pyridinium chloride (NDPC). The molar solubility of NB increased gradually from 2.3 ×10−6 to 8.6 × 10−6 (mol L−1) by raising the SDS concentration. The proposed natural surfactant, shikakai (SHI) was also facilitated the solubility of NB in the aqueous medium about threefold than water alone. The λmax of Nile blue shifted to longer wavelength and finally disappeared as the pH turned from acidic to alkaline. It has been concluded that the presence of SDS and SHI in the various biological applications can reduce the amount of NB and hence poses less hazardous effects to human health and the environment.