Characterization and application of a chlorine microelectrode for measuring monochloramine within a biofilm

Chlorine microelectrodes with tip sizes of 5–15 μm were fabricated, fully characterized and evaluated under various environmental conditions, and used to measure high spatial resolution monochloramine profiles in biofilm. The chlorine microelectrode showed response to total chlorine, including free chlorine, monochloramine, and dichloramine under various conditions. Where monochloramine dominates the system at pH 8.0 and 4:1 Cl2:N, the chlorine microelectrode had sensitivity toward monochloramine concentrations (0.1–30.0 mg Cl2/L) at an applied potential of +550 mV (Ag/AgCl reference electrode) and 23 °C, and it was independent of pH ranges typical of drinking water (pH 6–9). Even though the electrode response shifted with DO changes, a linear relationship existed with monochloramine concentration for a given DO concentration. As a result, a 3D (response vs. DO vs. monochloramine concentration) calibration curve was required with DO present. Ultimately, this research will lead to the in situ application of chlorine microelectrodes for measurement of monochloramine within chloraminated drinking water system biofilm and, along with other microelectrodes (e.g. ammonia, pH, DO), will aid in elucidating nitrification phenomena occurring in the biofilm.