Published:Journal of Chromatographic Science,
ISSN 0021-9665Volume
40, Number 8, September 2002, pp. 447-456
Improving the Recoveries of Unstable N-Chloramines Determined
by Liquid Chromatography–Postcolumn Electrochemical Detection*
Mary Bedner[1],[2], William A. MacCrehan]2], and George R. Helz[1]
[1]Department of Chemistry and Biochemistry, University of Maryland, College
Park, MD 20742 and
[2]Analytical Chemistry Division, National Institute of Standards and Technology,
Gaithersburg, MD 20899
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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