Improving the recoveries of unstable N-chloramines determined by liquid chromatography-postcolumn electrochemical detection

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Abstract

Liquid chromatographic (LC) measurement of individual N-chloramines, which are key byproducts of wastewater and drinking water chlorination, could lead to more effective control of water disinfection. Such measurements are challenging because of analyte instability. A detector selective for N-chloramines is constructed based on postcolumn derivatization with iodide followed by reductive detection of the iodine product at a glassy carbon electrode. In flow injection (FIA) mode, the detector gives identical responses for a test set of four chemically diverse N-chloramines. In the LC mode, losses of the test compounds are observed when LC and FIA responses are compared and quantitated by introducing a relative response factor (RRF). Using the RRF, N-chloramine recoveries are evaluated as a function of multiple LC separation parameters. The highest recoveries are obtained using a reversed-phase (C18) column with an acetonitrile mobile phase and a pH 7.02 aqueous phosphate buffer. With these conditions, linear calibration curves are obtained for all test N-chloramines. The detection limits obtained are in the low 10-7-mol/L range, which is nearly tenfold better than previously reported and 10-1000-fold lower than total residual chlorine concentrations typically found in disinfected water and wastewater.

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Bedner, M., MacCrehan, W. A., & Helz, G. R. (2002). Improving the recoveries of unstable N-chloramines determined by liquid chromatography-postcolumn electrochemical detection. Journal of Chromatographic Science, 40(8), 447–455. https://doi.org/10.1093/chromsci/40.8.447

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