Determination of non-ionic surfactants in waste water by direct extraction with Fourier transform infrared spectroscopic detection

Abstract

Non-ionic surfactants in waste water can be extracted and concentrated in dichloromethane using a simple salting-out procedure. The characteristic C—O—C stretch vibration at 1110 cm^–1 is then utilized to measure surfactant concentration at levels ranging from 0.1 to 50 mg l^–1. Relative standard deviations vary from 15% at the 10 mg l^–1 level for a single-step extraction, to 5% at the 1 mg l^–1 level for multiple extraction followed by evaporation and reconstitution. Soaps are the only major interference found for the technique. Comparison of this procedure with the commonly used cobaltothiocyanate method indicates that the combination of direct extraction and Fourier transform infrared detection is more accurate in determining non-ionic surfactants in aqueous solution from the viewpoint of recovery. Various levels of response were observed when analysing samples of different waste waters. The procedure is significantly more rapid when using the single-step extraction and is easily calibrated.