Why hypochlorite in water cannot be detected by ion chromatography?
Free chlorine (FC), primarily existing as hypochlorite anion in alkaline water (pK a 7.5), could theoretically be analyzed by an ion chromatography (IC) system. However, the feasibility of direct FC detection by IC remains controversial in previous researches. To address this issue, this study systematically examined the fate of FC under varying IC eluent pH, anion exchange column (AEC) types, detectors, and suppression conditions. The results ultimately disprove it and show that the primary obstacle to direct FC analysis with IC system is its transformation: 31 %–41 % became Cl - and 59 %–69 % became immobile organic chloramines in AEC, due to its reaction with quaternary ammonium compounds (QACs) in AECs. Moreover, IC analysis of Cl - might be interfered by coexisting FC, although FC concentrations are typically much lower than Cl - . Eluent suppressor can also consume FC even when residual FC after AEC is limited. In contrast, variations in water pH do not affect FC stability, and a UV detector effectively distinguishes FC from other anions. This study hence for the first time elucidates several FC consumption mechanisms in IC system, which represent key barriers hindering FC analysis by IC, and accordingly provide some guidance on future efforts to develop novel AEC to overcome these barriers.
危险品化学品经营许可证（带存储）