Toward continuous amperometric gas sensing in ionic liquids: rationalization of signal drift nature and calibration methods

Abstract

Sensor signal drift is the key issue for the reliability of continuous gas sensors. In this paper, we characterized the sensing signal drift of an amperometric ionic liquid (IL)-based oxygen sensor to identify the key chemical parameters that contribute to the signal drift. The signal drifts due to the sensing reactions of the analyte oxygen at the electrode/electrolyte interface at a fixed potential and the mass transport of the reactant and product at the electrode/electrolyte interface were systematically studied. Results show that the analyte concentration variation and the platinum electrode surface activity are major factors contributing to sensing signal drift. An amperometric method with a double potential step incorporating a conditioning step was tested and demonstrated to be useful in reducing the sensing signal drift and extending the sensor operation lifetime. Also, a mathematic method was tested to calibrate the baseline drift and sensing signal sensitivity change for continuous sensing. This study provides the understanding of the chemical processes that contribute to the IL electrochemical gas (IL-EG) sensor signal stability and demonstrates some effective strategies for signal drift calibration that can increase the reliability of the continuous amperometric sensing. Graphical Abstract ᅟ.

Characterization of the Ionic Liquid/Electrode Interfacial Relaxation Processes Under Potential Polarization for Ionic Liquid Amperometric Gas Sensor Method Development

“…In our previous work on the IL-EG oxygen sensor, we reported that the sensor signal stability is influenced by the analyte concentration gradient since the mass transport is rather slow in the IL due to its relative high viscosity. As shown in Figure , a constant potential amperometric sensor shows several features: (1) When a constant potential is applied, a double layer charge current flows.…”

“…These studies suggested a slow relaxation process at the IL/electrode interface under an external potential polarization in the IL electrolytes. − This slow relaxation process of the IL/electrode interface to a potential step can result in a slow drift of the baseline that is detrimental for continuous and real-time amperometric sensing. In our previous work on the IL-EG oxygen sensor, we characterized the sensor signal stability at various oxygen concentrations and noticed that slow mass transport is one of the key aspects that cause the sensor signal drift on a continuous-use basis. An earlier study by our group focusing on the IL/electrode interface morphologies at different potentials reported that the ions near the IL/electrode interface become more organized at the application of a feature potential .…”

New innovations in ionic liquid–based miniaturised amperometric gas sensors

“…Among the various Clark-cell type designs, some highlights include the detection of oxygen [22,23,25] and hydrogen [24,26] gases. Figure 2 shows a schematic of a sensor device used for detecting hydrogen gas with fast response times; hydrogen flows into the cell, where it diffuses through a gas-permeable membrane to the sensing electrode and is oxidised.…”

“…Excellent reproducible signals are observed, with ascending and descending concentration currents almost identical. The issue of signal drift for a continuous "real-time" sensor was also discussed by the same group [25] in the context of oxygen detection.…”

Empiric Unsupervised Drifts Correction Method of Electrochemical Sensors for in Field Nitrogen Dioxide Monitoring

“…However, several issues impede these systems to provide data with quality similar to those obtained by the analyzers [ 15 ]. The mechanism of the sensor drifts is clearly presented in [ 16 ]. The main reason is that electrochemical sensors are affected by environmental factors, mainly the temperature and humidity [ 17 , 18 ].…”