Electrochemical Detection of Free-Chlorine in Water Samples Facilitated by In-Situ pH Control Using Interdigitated Microelectrodes

Abstract

Residual free-chlorine concentration in water supplies is a key metric studied to ensure disinfection. High residual chlorine concentrations lead to unpleasant odours and tastes, while low concentrations may lead to inadequate disinfection. The concentration is most commonly monitored using colorimetric techniques which require additional reagents. Electrochemical analysis offers the possibility for in-line analysis without the need for additional reagents. Electrochemical-based detection of chlorine is influenced by the solution pH, which defines the particular chlorine ionic species present in solution. As such, controlling the pH is essential to enable electrochemical based detection of residual chlorine in water. To this end, we explore the application of solid state interdigitated electrodes to tailor the in-situ pH of a solution while simultaneously detecting free-chlorine. Finite element simulations and subsequent electrochemical characterization, using gold interdigitated microelectrode arrays, were employed to explore the feasibility of an in-situ pH control approach. In practice, the approach converted residual chlorine from an initial mixture of two species (hypochlorous acid and hypochlorite ion), to one species (hypochlorous acid). Chlorine detection was shown in water samples using this exploratory method, resulting in a two-fold increase in signal response, compared to measurements without pH control. Finally, tap water samples were measured using the in-situ pH control method and the results showed excellent correlation (within experimental error) with a commercial instrument, demonstrating the efficacy of the developed technique. This work establishes the possibility of deploying an electrochemical based reagent-free, in-line chlorine sensor required for water distribution networks.

Portable Data Acquisition System for Nano and Ultra-Micro Scale Electrochemical Sensors

“…To present the full range of functionality of the system and verify its use as a portable potentiostat, a calibration curve was produced for the detection of dissolved oxygen in river water. This was performed using recently developed ultra microband electrochemical sensors [21,22]. As seen in Fig.…”

3,3′,5,5′-tetramethylbenzidine as multi-colorimetric indicator of chlorine in water in line with health guideline values

“…should be larger than 2400 mg L −1 . The standard analytical methods for the determination of chlorine in natural and treated waters are based on electrochemical techniques, iodometry, and absorption spectrophotometry [5][6][7][8][9][10], usually requiring devices for signal transduction or UV lamp for fluorescence emission. However, several kits for household chlorine test are present in the market for colorimetric quantification of chlorine concentration based on monochromatic indicators.…”

Reagent Free Electrochemical-Based Detection of Silver Ions at Interdigitated Micro Electrodes Using in Situ pH Control

“…Despite the form of chlorine used (gaseous chlorine, calcium hypochlorite or sodium hypochlorite), a combination of hypochlorous acid (HOCl) and hypochlorite ion (OCl -) will be present in tap water as "free available chlorine" in line with statutory regulations. In acidic conditions, the HOCl species dominates, which is a more reactive form of chlorine [33,34]. Although several authors have reported electrochemical approaches for silver detection in real water samples, most of these reports had to (i) first acidify the solution using an acid or (ii) add additional electrolyte prior to performing the measurements [15][16][17]35].…”