Sensitive Potentiometric Method for Determination of Micromolar Level of Polyethoxylated Nonionic Surfactants in Effluents

The Metrohm NIO surfactant electrode has been used as endpoint indicator for potentiometric titration of low concentration level of polyethoxylated nonionic surfactants. This can be achieved by using of a diluted titrant concentration, thus reducing the amount of precipitate formed during titration and preventing the electrode deterioration. The solutions of low levels (down to 10(-6) mol/L) of selected nonionic surfactants containing 5 to 23 EO groups were successfully titrated with diluted (as low as 10(-4) mol/L) sodium tetraphenylborate as standard anionic titrant, increasing up to 20 times the sensitivity of the method. The low surfactant concentration has been determined in synthetic formulations of widely used detergent products and industrial waste waters. The titration end-point has been determined by applying extended Savitzky-Golay least-squares regression. The accuracy and precision has been evaluated by using the standard addition method. Relative standard deviation within results was between 3.4 and 12.8% depending on the sample complexity and the surfactant concentration level.