Salt-induced metachromatic behaviour of an azo dye in aqueous solution

Abstract

Addition of substantial amounts of simple electrolytes into basic aqueous methyl orange solutions causes a marked decrease of the intensity of the light absorption of the dye in the visible range and the appearance of a total new absorption band at 358 nm. Addition of a non-electrolyte such as urea shows no such effect.

The phenomenon is attributed to interactions between the added ions and the electrons of the chromophoric system.