Determination of partition coefficient of trace anionic surfactants in oil/water systems with visible spectrophotometry

The spectrophotometric method for determining trace anionic surfactant concentration in alkaline aqueous solution is extended to determine anionic surfactant concentration in oil phase and is successfully applied to determine partition coefficient of trace surfactants in oil/water systems.It is found that in both cases that the concentration of surfactant in oil or aqueous solution is to be determined,the absorbance of chloroform layer depends only on the free cationic surfactant concentration in measuring system.The absorbance-concentration corelation of a single cationic surfactant,therefore,can be worked out as operatinge equations.For the determination of surfactant concentrations in both the oil and aqueous solutions,the operating equations show different slope and the minimum concentrations detectable can be as low as 5×10~(-5) mol·L~(-1) and (1×(10~(-6)) mol·L~(-1)),respectively.