Determination of fluorescent whitening agents in environmental waters by solid-phase extraction and ion pair liquid chromatography–tandem mass spectrometry

A comprehensive method for the trace determination of four stilbene-type disulfonate and one distyrylbiphenyl-type fluorescent whitening agents (FWAs) in environmental water samples was developed and validated. Various solid-phase extraction (SPE) cartridges were investigated. The newly developed Oasis WAX (weak mixed-mode anion exchange and reversed-phase sorbent) SPE cartridge provides the optimal sample extraction results. The analytes were then identified and quantitated by liquid chromatography–electrospray ionization tandem mass spectrometry (HPLC–ESI-MS–MS) in negative ionization mode, applying di-n-hexylammonium acetate (DHAA) as the ion-pairing reagent in mobile phase. Limits of quantitation (LOQs) were established between 4 and 18 ng/l in 50 ml of water samples. Intrabatch and interbatch precision with their accuracy at two concentration levels were also investigated. Precision for these five FWAs, as indicated by RSD, proved to be less than 13 and 11%, respectively, for intra- and interbatch. Accuracy, expressed as the mean recovery, was between 68 and 97%. The method was finally applied to environmental water samples, showing the occurrence of five FWAs in both river water and wastewater treatment plant (WWTP) effluent samples.