MONITORING AROMATIC SURFACTANTS AND THEIR BIODEGRADATION INTERMEDIATES IN RAW AND TREATED SEWAGES BY SOLID-PHASE EXTRACTION AND LIQUID-CHROMATOGRAPHY

On the basis of solid-phase extraction, a simple procedure for determining simultaneously two aromatic surfactant classes, i.e., linear alkylbenzene sulfonates (LAS) and nonylphenol polyethoxylates (NPEO), as well as their biodegradation intermediates in raw and treated sewages is presented. This procedure involved passing 10 and 100 mL of an influent and effluent water sample, respectively, through a 1-g graphitized carbon black (GCB) extraction cartridge. By exploiting the presence of positively charged active centers on the GCB surface, we succeeded in fractionating the complex mixture of the analytes considered by differential elution. The first fraction contained NPEO and nonylphenol (NP). The second fraction contained the carboxylated biotransformation products of NPEO, i.e., nonylphenoxy carboxylic acids (NPEC). Finally, the last fraction contained LAS and their metabolites, i.e., carboxylic sulfophenyl acids (SPC). By suitably adjusting the chromatographic conditions, any group of analytes was subfractionated and quantified by liquid chromatography with fluorometric detection. Recoveries of all compounds of interest ranged between 89 % and 99%. This procedure was empolyed for 1 year to assess monthly the concentrations of the analytes considered in raw and treated sewages of a mechanical-biological treatment plant.