Methods for the determination of the anionic surfactant Dowfax 8390 are described. Dowfax is a complex mixture of various alkylated and sulfonated diphenyl oxides. The primary component of Dowfax is monoalkylated disulfonated diphenyl oxide (MADS). This work uses ion pairing chromatography and reverse phase chromatography. Ion pairing chromatography provides a simple and fast method for quantitation of the total concentration of Dowfax surfactant in aqueous solutions. It is shown that suppressed conductivity detection and optical detection at 210 nm have comparable sensitivity. A quantitation limit of 48.4 ppm is achieved with 400 μl injection. The separation of 11 components in Dowfax is achieved using gradient reverse phase chromatography.