Elimination of Oxygen Interference in the Electrochemical Detection of Monochloramine, Using In Situ pH Control at Interdigitated Electrodes.

Ian Seymour,Benjamin O’Sullivan,Pierre Lovera,Alan O’Riordan,James F Rohan

doi:10.1021/acssensors.0c02264

Abstract

Disinfection of water systems by chloramination is a method frequently used in North America as an alternative to chlorination. In such a case, monochloramine is used as the primary chlorine source for disinfection. Regular monitoring of the residual concentrations of this species is essential to ensure adequate disinfection. An amperometric sensor for monochloramine would provide fast, reagent-free analysis; however, the presence of dissolved oxygen in water complicates sensor development. In this work, we used in-situ pH control as a method to eliminate oxygen interference by conversion of monochloramine to dichloramine. Unlike monochloramine, the electrochemical reduction of dichloramine occurs outside the oxygen reduction potential window and is therefore not affected by the oxygen concentration. Potential sweep methods were used to investigate the conversion of monochloramine to dichloramine at pH 3. The pH control method was used to calibrate monochloramine concentrations between 1 and 10 ppm, with a detection limit of 0.03 ppm. Tests were carried out in high alkalinity samples, wherein it was found that the sensitivity of this method effectively remained unchanged. Monochloramine was also quantified in the presence of common interferents (copper, phosphate, and iron) which also had no significant impact on the analysis.

Highlights

Disinfection of water systems is crucial to ensure safety of potable water, and is typically done using hypochlorous acid (HOCl) as a disinfecting agent.[1, 2] The measurement of the residual chlorine is important as it can determine the progress of the disinfection process
We have recently shown that an in-situ pH control method can facilitate the detection of hypochlorous acid by protonation of the hypochlorite ion.[34]
Platinum was plated onto one comb of the interdigitated array which was to be used as the protonator electrode

Summary

Introduction

Disinfection of water systems is crucial to ensure safety of potable water, and is typically done using hypochlorous acid (HOCl) as a disinfecting agent.[1, 2] The measurement of the residual chlorine is important as it can determine the progress of the disinfection process. MCA treated water has been shown to have significantly lower concentrations of resulting THMs.[14] Treatment with MCA does have its disadvantages, most typically the formation of dichloramine (DCA) and trichloramine (TCA), which form as chlorine content increases, or the sample pH becomes acidic.

Results

Conclusion