Monochloramine-sensitive amperometric microelectrode: optimization of gold, platinum, and carbon fiber sensing materials for removal of dissolved oxygen interference

Abstract

Monochloramine electrochemical determination in an aqueous system using newly fabricated gold and platinum microelectrodes was investigated to optimize sensor operation and to eliminate dissolved oxygen (DO) interference during monochloramine measurements. Carbon fiber microelectrodes were also compared for reference purposes. Gold and platinum microelectrodes exhibited no oxygen interference during monochloramine measurement and provided a linear relationship when operated at +150 and +300 mV vs. Ag/AgCl over a wide concentration range (0–4.2 mg Cl2/L), respectively. The carbon fiber microelectrode with 7-μm tip diameter was not sufficiently sensitive to monochloramine concentrations for detailed study. The baseline signal of both gold and platinum microelectrodes (i.e., signal without monochloramine) was near zero. With the same geometric tip diameter (20-μm tip diameter), gold microelectrodes resulted in better amperometric electrode response to monochloramine than platinum microelectrodes; gold microelectrodes had a higher sensitivity (52 ± 0.7 vs. 18 ± 0.07 pA/[mg Cl2/L]) and lower detection limit (0.12 ± 0.013 vs. 0.33 ± 0.10 mg Cl2/L), resulting in gold as the preferred microelectrode material. The developed gold microelectrode will allow accurate in situ monochloramine determination in biofilm while eliminating the confounding effects of oxygen interference.