Method for determining surfactant concentration in aqueous solutions

The present method provides a single-phase technique in which an ionic strength adjuster and a water insoluble dye are added to a sample of an aqueous solution containing an unknown quantity of a known surfactant. Even at surfactant concentrations well below the critical micelle concentration (CMC) of the aqueous sample, the addition of an ionic strength adjuster induces the surfactant to form micelles. These micelles absorb the water insoluble dye, thereby imparting a known color to the aqueous sample being tested. The color intensity of the treated aqueous sample is directly related to the concentration of the surfactant in the sample and, through the use of calibration curves prepared from samples of know concentration, can be used to determine the surfactant concentration.