Non-target screening and novel methods based on mass spectrometry detection for identification of unknown disinfection byproducts

Abstract

Disinfection by-product (DBP) mixtures formed during disinfection processes are highly complex. Despite the extensive research conducted in this field, only about half of the halogenated material formed has been characterized. Liquid chromatography or gas chromatography coupled to low, high or ultra-high resolution mass spectrometry (MS) have been the main analytical tools used to uncover chemicals in DBP mixtures. This chapter reviews the main approaches and workflows based on mass spectrometry applied for the identification of unknown DBPs in disinfected waters. Low resolution MS approaches include the evaluation of ion clusters that produce halogens (Cl, Br and I), the monitoring of expected fragment ions and MS/MS transitions, and the ‘target suspect approach’ that consists of obtaining standards of suspect DBPs and creating a sensitive and selective target method for their detection. In the case of high resolution MS, two main workflows are applied: suspect screening and non-target screening. The main applications include characterization of halogenated DBP mixtures and discovery of halogenated DBPs, ozonation DBPs, DBPs that originate from organic micro-pollutants, amino-containing DBPs (stable isotope labelling method), and N -chlorinated dipeptides (precursor ion exclusion method). Non-target screening with ultra-high resolution MS instruments has been primarily used to characterize natural organic matter and DBP mixtures. Workflows used to treat non-target data obtained with high resolution and ultra-high resolution MS approaches are also reviewed. Finally, new opportunities to discover DBPs in water, such as the use of effect directed analysis and ion mobility, are also discussed.