Determination of free chlorine based on ion chromatography—application of glycine as a selective scavenger

Abstract

Free available chlorine (FAC) is the most widely used chemical for disinfection and in secondary disinfection; a minimum chlorine residual must be present in the distribution system. FAC can also be formed as an impurity in ClO2 production as well as a secondary oxidant in the ClO2 application, which has to be monitored. In this study, a new method is developed based on the reaction of FAC with glycine in which the amine group selectively scavenges FAC and the N-chloroglycine formed can be measured by ion chromatography with conductivity detector (IC-CD). Utilizing IC for N-chloroglycine measurement allows this method to be incorporated into routine monitoring of drinking water anions. For improving the sensitivity, IC was coupled with post-column reaction and UV detection (IC-PCR-UV), which was based on iodide oxidation by N-chloroglycine resulting in triiodide. The method performance was quantified by comparison of the results with the N,N-diethyl-p-phenylenediamine (DPD) method due to the unavailability of an N-chloroglycine standard. The N-chloroglycine method showed limits of quantification (LOQ) of 24 μg L−1 Cl2 and 13 μg L−1 Cl2 for IC-CD and IC-PCR-UV, respectively. These values were lower than those of DPD achieved in this research and in ultrapure water. Measurement of FAC in the drinking water matrix showed comparable robustness and sensitivity with statistically equivalent concentration that translated to recoveries of 102% for IC-CD and 105% for IC-PCR-UV. Repeatability and reproducibility performance were enhanced in the order of DPD, IC-CD, and IC-PCR-UV. Measurement of intrinsic FAC in the ClO2 application revealed that the N-chloroglycine method performed considerably better in such a system where different oxidant species (ClO2, FAC, chlorite, etc.) were present.

Novel insights into chlorine dioxide based disinfection mechanisms – investigation of the reaction with amino acids

“…24 However, previous research did not quantify the formed FAC. By using the glycine method, 28 it was possible to quantify intrinsic FAC, and thus, the yield of FAC could be determined. With the knowledge that ClO 2 − and FAC are formed in a 1 : 1 ratio, it seems reasonable that NAL-tyrosine reacts similarly to phenol, whereby ClO 2 − is formed in the first step of the reaction (electron transfer) and the second step leads to the formation of FAC ((oxygen transfer) for further details cf.…”

“…From the 15% FAC solution mentioned in the Chemicals and instruments section, an aliquot of 125 μL was diluted in 50 mL pure water. The FAC concentration was measured photometrically at λ = 292 nm ( ε 292 = 350 M −1 s −1 ) 28 by using a UV/vis photometer. One has to take into account that the concentration was determined by measuring the OCl − concentration.…”

“…, the sum of all inorganic chlorine species formed in the reaction of ClO 2 with compounds under study (Cl − , FAC, ClO 2 − , and ClO 3 − )) was measured in analogy to the procedure described by Abdighahroudi et al 2020. 28 In brief, a stock solution was prepared containing 5 mM phosphate buffer, 10 mM glycine, and 100 μM compound under study. The pH of the stock solution was set to 7.0 to mimic the conditions representative for typical microorganisms (pH of cytoplasm is between 7.0 and 7.4 (ref.…”

Reaction of Chlorine Dioxide with Saturated Nitrogen-Containing Heterocycles and Comparison with the Micropollutant Behavior in a Real Water Matrix

“…Further details (linear range, the limit of detection, etc.) can be found in Abdighahroudi et al 2020 …”

“…can be found in Abdighahroudi et al 2020. 52 Transformation products (TPs) of Pd and Cz were also analyzed using liquid chromatography high-resolution mass spectrometry (LC-HRMS) with a Q-Exactive Orbitrap mass spectrometer. For Pd analysis, a mixed mode column (SIELC Primesep 200 150 mm × 2.1 mm, 5 μM) and for Cz, a reversephase column (Phenomenex Kinetex C18 100 mm × 3 mm, 5 μm) were used.…”