Continuous Monitoring\nof Monochloramine in Water,\nand Its Distinction from Free Chlorine and Dichloramine Using a Functionalized\nGraphene-Based Array of Chemiresistors

Monochloramine (MCA) is commonly added to drinking water\nas a disinfectant\nto prevent pathogen growth. The generation of MCA at the treatment\nplant requires tight control over both pH and the ratio of free chlorine\n(FC) to ammonia to avoid forming undesirable byproducts such as dichloramine\n(DCA) and trichloramine (TCA), which can impart odor and toxicity\nto the water. Therefore, continuous monitoring of MCA is essential\nto ensuring drinking water quality. Currently, standard colorimetric\nmethods to measure MCA rely on the use of reagents and are unsuitable\nfor online monitoring. In addition, other oxidants can interfere with\nMCA measurement. Here, we present a solid-state, reagent-free MCA\nsensing method using an array of few-layer graphene (FLG) chemiresistors.\nThe array consists of exfoliated FLG chemiresistors functionalized\nwith specific redox-active molecules that have differential responses\nto MCA, FC, and DCA over a range of concentrations. Chemometric methods\nwere employed to separate the analytes’ responses and to generate\nmultivariate calibration for quantification. A minimum of three sensors\nare required in the array to maintain full functionality. The array\nhas been demonstrated to quantify MCA in buffered and tap water as\na low-cost, reagent-free approach to continuous monitoring.