Abstract
Usage of commercially available electrochemical gas sensors is currently limited by both the working range of the sensor with respect to temperature and humidity and the spikes in sensor response caused by sudden changes in temperature or humidity. Using a thermostatically controlled chamber, the sensor response of ammonia and hydrogen sulfide sensors was studied under extreme, rapidly changing levels of humidity with the aim of analyzing nebulized water samples. To protect the sensors from damage, the gas stream was alternated between a saturated gas stream from a Flow Blurring® nebulizer and a dry air stream. When switching between high and low humidity gas streams, the expected current spike was observed and mathematically described. Using this mathematical model, the signal response due to the change in humidity could be subtracted from the measured signal and the sensor response to the target molecule recorded. As the sensor response is determined by the model while the sensor is acclimatizing to the new humid conditions, a result is calculated faster than that by systems that rely on stable humidity. The use of the proposed mathematical model thus widens the scope of electrochemical gas sensors to include saturated gas streams, for example, from nebulized water samples, and gas streams with variable humidity.
Highlights
Low-cost electrochemical sensors have been widely used to monitor air quality or ensure industrial safety
The advantages of low cost; continuous; and, where required, high density measurements have led to electrochemical sensors being used in urban and industrial settings [2,3,4]
Before the effectiveness of low-cost electrochemical sensors in an extremely humid gas stream could be assessed, it was first necessary to understand the influence of this humid environment on the sensors
Summary
Low-cost electrochemical sensors have been widely used to monitor air quality or ensure industrial safety. To allow the use of low-cost electrochemical sensors for online water analysis, the compounds under investigation must be continuously extracted from the sample liquid. When combined with appropriate temperature, pressure, and pH control, a nebulizer-based extraction of dissolved substances into the gas phase could allow continuous monitoring of water samples using low-cost electrochemical sensors. To investigate the possibility of using low-cost electrochemical gas sensors to measure the levels of ammonia and hydrogen sulfide in water samples, a metallic nebulizer was constructed to allow the continuous extraction of water samples at a defined temperature. The extracted gas stream was analyzed using an algorithm to decouple the effect of humidity from the effect of target molecules on the low-cost electrochemical sensors This was integrated into a custom built user interface to allow online analysis of water samples
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