Detection of emerging disinfection by-products by reversed-phase ion-pair chromatography electrospray-ionization mass spectrometry in drinking water

A sensitive and specific methodology that allows unequivocal identification of polydiallyldimethylammonium chloride (PDADMAC) disinfection by-product it monomer diallyldimethylammonium chloride (DADMAC) in drinking water samples based on reversed-phase ion-pair chromatography–electrospray ionization – mass spectrometry was optimized. Ion-pair reagent heptafluorobutyric (HFBA) was found to play a crucial role in the optimization of chromatographic parameters. The chromatographic retention time was optimized by varying concentrations of ion-pair reagent, flow rate, and column temperature to enable good chromatographic retention and sensitivity of disinfection by-product of interest DADMAC in positive electrospray ionization and using selected ion monitoring (SIM) mode. The method was validated and showed good linear regression of 0.99 and a detection limit of 0.008 mg L⁻¹. The developed method was applied in a drinking water treatment plant operated by Mgeni Water in Durban, South Africa, to detect trace levels of the disinfection by-product of interest (DADMAC) at various points of the treatment process. The concentration of DADMAC in the water treatment plant ranged from not detected up to 0.65 mg L⁻¹. In addition, this work through mass spectrometry provides the first evidence of ion-pairing (465 m/z peak) between DADMAC and the reagent, which is a confirmation of online derivatization. Also, the use of ion-pair prevented dimerization of DADMAC (286 m/z peak) inside the ionization chamber leading to high sensitivity.