Batchwise and Flow-Injection Methods for the Spectrophotometric Determination of Anionic Surfactants with 4-(4-N,N-Dimethylaminophenylazo)-2-methylquinoline

Abstract

solvent-extraction Spectrophotometric method for the determination of anionic surfactants in water was developed with -(4-N, N-dimethylaminophenylazo)-2-methylquinoline (MQ) by batchwise and flow-injection techniques. The ion associates of MQ with anionic surfactants extracted into an organic phase showed a blue shift of the maximum absorption wavelength; their molar absorptivities were 4.5×10(4)l mol(-1) cm(-1) at 560nm. In the batchwise method, a 40-fold extraction concentration was possible. In the 20-fold concentration, the calibration graph was linear at concentration ranging from 1×10(-8)M to 7.5×10(-7)M of anionic surfactants, and the mean absorbances of the reagent blank and the 5×10(-7)M anionic surfactant (dodecylsulfate : LS(-)) were 0.024 and 0.518, respectively; the relative standard deviation for 10 measurements of 5×10(-7)M LS(-) was 0.28%. Foreign ions generally existing in river water did not interfere with the determination. This solvent-extraction spectrophotometric method was satisfactorily applied to a flow-injection method. The reagent MQ was recycled and repeatedly used at least for 7 months, and the efficiency of the reagent has not changed during at least this period.