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

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.

The nitrogen effect on the oxidation behaviour of Ti6242S titanium-based alloy: contribution of atom probe tomography

At high temperatures under oxidizing environments, titanium-based alloys form an oxide scale and dissolve large amount of oxygen in their metallic matrix. Oxygen dissolution is a cause of embrittlement. Nitrogen is a secondary oxidant, which also dissolves in titanium during oxidation in air. Oxidation experiments of Ti-6Al-2Sn-4Zr-2Mo-0.1Si titanium-based alloy at 650 °C for 1000 h in synthetic air (20%O2- 80%N2) and in a mixture of 20%O2-80%Ar, showed that nitrogen reduces both oxide scale growth and oxygen dissolution. Atom probe tomography revealed that nitrogen effect is due to the formation of an interfacial layer of nitride Ti2N but also to the formation of a nitrogen rich a-Ti-based solid solution, which both act as difiusion barriers for oxygen because of their low oxygen solubility.

Ozonation of haloacetic acid precursor using phenol as a model compound: effect of ozonation by-products

The formation pattern of haloacetic acids (HAAs) was investigated using phenol as a model precursor of HAAs, and the oxidation by-products formed from phenol ozonation, such as hydroquinone, catechol, glyoxal, glyoxylic acid and oxalic acid, were also chlorinated to measure the HAAs formation potential (HAAFP). Of these, phenol showed the highest reactivity with chlorine, yielding the most HAAFP. Even though HAAFP of the tested by-products was lower than that of phenol, it was confirmed that all by-products can act as the precursor of HAAs. Regarding the ozonation of phenol-containing water, the efficiency of ozone in controlling HAAs can be reduced by the formation of oxidation by-products. When comparing conditions for pH 7 and 3, the ozonation for pH 7 was more effective in removing the overall HAA precursors than the ozonation for pH 3. This result was attributed to complete oxidation by the production of the secondary oxidant, such as the OH radical (OH·) from ozone decay, and ionization of phenol.