Evaluation of Ion Chromatography Methods for Bromate Determination in Wastewaters

As oxidative processes are increasingly employed for the removal of trace substances in advanced wastewater treatment, as required by, among others, by the EU urban Wastewater treatment directive, disinfection by-products, particularly bromate are becoming increasingly important. This study presents a comprehensive intra- and interlaboratory evaluation of four ion chromatography (IC) based methods for the determination of bromate in wastewater: conductivity detection (IC-CD), post-column reaction with UV/Vis detection (IC-PCR-UV/Vis), high-resolution mass spectrometry (IC-ESI-HRMS), and inductively coupled plasma mass spectrometry (IC-ICP-MS). Performance parameters were assessed in ultrapure water and verified across different wastewater matrices, including influent, secondary clarifier effluent, and final effluent of a municipal wastewater treatment plant. IC-CD achieved a LOQ of 1.4 µg/L in ultrapure water but exhibited strong matrix dependency in untreated wastewater. In treated wastewater, the verified LOQs were sufficiently low to allow quantification below the regulated drinking water limit (10 µg/L). IC-PCR-UV/Vis and IC-ICP-MS demonstrated robust performance across all investigated matrices, with a LOQ of 1.0 µg/L and consistently reliable precision (<5%) and recoveries (90-110%), making these methods suitable for both treated and untreated wastewater. IC-ESI-HRMS provided the lowest LOQ (0.07 µg/L) though requiring dilution in untreated wastewaters due to matrix effects. Interlaboratory validation confirmed that IC-CD is only suitable for treated wastewater, whereas IC-PCR-UV/Vis is broadly applicable across treated and untreated wastewaters. Overall, IC-PCR-UV/Vis represents the most practical method for routine bromate monitoring in wastewaters. Mass spectrometry-based approaches demonstrated enhanced selectivity and lower LODs, while enabling multi- analyte analysis, albeit with higher instrumental complexity. However, their broader applicability for routine wastewater monitoring requires further interlaboratory evaluation.