Determination of ammonia in wastewaters containing high concentrations of surfactants by flow injection potentiometry with on-line sample clean-up

It is demonstrated that surfactants lead to problems in the analysis of ammonia in gas-diffusion flow injection by wetting the membrane to allow transport of potentially interfering species to the detector. An on-line clean-up procedure, involving use of an activated carbon cartridge, is described for the removal of ionic and non-ionic surfactants (up to 1000 mg l(-1)) and other organic compounds from aqueous samples. Ammoniacal nitrogen was determined in synthetic samples by gas-diffusion flow injection with a nonactin-based potentiometric sensor used as the detector for the ammonium ion. Analyses could be performed at a sampling rate of ca. 25 h(-1) and the cartridge was effective for at least 1000 injections of 50 mu l samples in the concentration range 1-180 mg l(-1). The procedure was applied to the analysis of wastewaters and was found to be efficient in removing ionic and non-ionic surfactants from acidified (pH 1) samples. (C) 1998 Elsevier Science B.V.