Non-suppressed ion chromatography-tandem electrospray mass spectrometry using a short column for simultaneous analysis of dichloroacetic acid, trichloroacetic acid, and bromate: aqueous ammonia as the eluent additive

Dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), and bromate (BrO₃^-) are disinfection byproducts (DBPs) formed during drinking water treatment and pose health risks. Rapid and reliable detection of these DBPs is essential for ensuring water safety. Non-suppressed ion chromatography (IC)-electrospray ionization mass spectrometry (IC-ESI-MS/MS) offers a promising approach for simultaneous analysis of organic haloacetic acids (HAAs) and inorganic oxyhalides, but previous methods using toxic methylamine can pose health risks. Herein, a new rapid non-suppressed IC-ESI-MS/MS method using a short AG18 guard column (13 μm, 2 mm × 50 mm) with aqueous ammonia as the alkaline modifier was developed for the simultaneous quantification of DCAA, TCAA, and BrO₃^-. This method allows direct sample injection without pretreatment and achieves sub-μg L^-1 detection limits within 5 minutes. Aqueous ammonia (0.4 M) and acetonitrile were used as mobile phases in a gradient elution mode, providing good linearity (<i>R</i>² >0.995), low limits of quantification (0.48-1.13 μg L^-1), and high recoveries (76.3-107.3%). Intra-day (<i>n</i> = 9) and inter-day (3 days, <i>n</i> = 9) precision were validated with relative standard deviations of 5.8-8.9% and 6.4-7.7%, respectively. The method also demonstrated limited matrix interference from common water parameters such as Cl^-, SO₄^2-, HCO₃^-/CO₃^2-, and natural organic matter (NOM), making it suitable for real water analysis. The applicability of this method was confirmed by monitoring DBP formation during the chlorination of NOM, showing that two-step chlorine dosing strategies reduce DBP formation compared to single-stage dosing. This newly established method provides a robust and efficient tool for DBP monitoring in drinking water treatment processes.