Spectroscopic studies of the interaction between methylene blue-naphthol orange complex and anionic and cationic surfactants.

Initially, the absorbance of MB at 665 nm decreased rapidly with increasing sodium dodecyl sulfate (SDS) concentration, but increased gradually above about 2.3x10(-3) M. However, the absorbance of MB was almost independent of the cetyltrimethylammonium bromide (CTAB) concentration.