Potentiometric sensing array for monitoring aquatic systems

Abstract

Since aquatic environments are highly heterogeneous and dynamic, there is the need in aquatic ecosystem monitoring to replace traditional approaches based on periodical sampling followed by laboratory analysis with new automated techniques that allow one to obtain monitoring data with high spatial and temporal resolution. We report here on a potentiometric sensing array based on polymeric membrane materials for the continuous monitoring of nutrients and chemical species relevant for the carbon cycle in freshwater ecosystems. The proposed setup operates autonomously, with measurement, calibration, fluidic control and acquisition triggers all integrated into a self-contained instrument. Experimental validation was performed on an automated monitoring platform on lake Greifensee (Switzerland) using potentiometric sensors selective for hydrogen ions, carbonate, calcium, nitrate and ammonium. Results from the field tests were compared with those obtained by traditional laboratory analysis. A linear correlation between calcium and nitrate activities measured with ISEs and relevant concentrations measured in the laboratory was found, with the slopes corresponding to apparent single ion activity coefficients γ(*)(Ca(2+)) = 0.55(SD = 0.1mM) and γ(*)(NO(3)(-)) = 0.75(SD = 4.7μm). Good correlation between pH values measured with ISE and CTD probes (SD = 0.2 pH) suggests adequate reliability of the methodology.

Electroanalysis with Membrane Electrodes and Liquid–Liquid Interfaces

“…Bakker’s group developed a potentiometric sensing array, including a self-contained electrochemical multichannel module, to measure electrolyte concentrations in freshwater lakes . The sensor array was mounted on a floating platform, and lake water was pumped at varying depths for analysis.…”

Optical Sensing with a Potentiometric Sensing Array by Prussian Blue Film Integrated Closed Bipolar Electrodes

“…In environmental analysis, potentiometric sensor arrays have been used in the quantitative analysis of pH, potassium, sodium, calcium, nitrate, carbonate, and ammonium. 15,19,20 Array sensing platforms based on optical sensors have become important for the determination of multiple analytes, to assess near-complete chemical information for a given sample, and to achieve real-time chemical imaging. 21−24 However, traditional optical sensors may be negatively affected by turbid or colored samples, as the working ranges are comparatively narrow and the detection of ions requires extra-thermodynamic assumptions that are not always well understood or accepted.…”

Ion-to-electron capacitance of single-walled carbon nanotube layers before and after ion-selective membrane deposition

“…All of these methods have different characteristics and sensitivities. At the same time, it is apparent that nitrate-selective electrodes represent a rare class of sensor that allows one to perform a continuous in situ monitoring of nitrate concentration with a detection limit below 1 μM using low-power portable instruments [23,39].…”