Enhanced trace detection of haloacetic acids in water using on-line isotachophoresis–capillary zone electrophoresis coupled with liquid–liquid extraction

Haloacetic acids (HAAs) are toxic disinfection by-products formed during water chlorination. This study presents an optimized method for the trace determination of five HAAs: monochloro-, dichloro-, trichloro-, mono-, and dibromoacetic acids, using an on-line isotachophoresis-capillary zone electrophoresis (ITP-CZE) with UV detection at 200 nm. To enhance the sensitivity, a pre-column liquid-liquid extraction (LLE) step was introduced for sample preconcentration. The combined ITP pre-focusing and optimized background electrolyte containing 3-(N, N-dimethyldodecylammonio)propanesulfonate enabled baseline separation of all analytes at pH 3.4. Method validation showed excellent linearity (R² > 0.998), precisions (CVs ≤ 7%), and recoveries (82-118%), all within the U.S. EPA acceptable range (70-130% recovery, CV ≤ 20%). Incorporation of the LLE step reduced detection limits to 0.6-3.2 µg/L, well below the regulatory threshold of 60 µg/L for the total HAA concentration in drinking water. The validated method was successfully applied to tap and bottled water samples. This ITP-CZE-LLE approach offers a rapid, selective, and environmentally friendly alternative to chromatographic techniques for monitoring HAAs in water quality control.