Organoleptic Analysis of Drinking Water Using an Electronic Tongue Based on Electrochemical Microsensors

Abstract

The standards that establish water's quality criteria for human consumption include organoleptic analysis. These analyses are performed by taste panels that are not available to all water supply companies with the required frequency. In this work, we propose the use of an electronic tongue to perform organoleptic tests in drinking water. The aim is to automate the whole process of these tests, making them more economical, simple, and accessible. The system is composed by an array of electrochemical microsensors and chemometric tools for multivariable processing to extract the useful chemical information. The array of sensors is composed of six Ion-Sensitive Field Effect Transistors (ISFET)-based sensors, one conductivity sensor, one redox potential sensor, and two amperometric electrodes, one gold microelectrode for chlorine detection, and one nanocomposite planar electrode for sensing electrochemical oxygen demand. A previous study addressed to classify water samples according to taste/smell descriptors (sweet, acidic, salty, bitter, medicinal, chlorinous, mouldy, and earthy) was performed. A second study comparing the results of two organoleptic tests (hedonic evaluation and ranking test) with the electronic tongue, using Partial Least Squares regression, was conducted. The results show that the proposed electronic tongue is capable of analyzing water samples according to their organoleptic characteristics, which can be used as an alternative method to the taste panel.

Keywords: drinking water samples; electrochemical microsensors; electronic tongue; multivariate methods; organoleptic tests.

Figure 1

PCA score plot using the three first PC for the 16 synthetic water samples.

Figure 2

PCA (a) score plot and (b) loading plot obtained using the analytical data carried out by standard methods in the accredited laboratory. In the loading plot, the grey circle corresponds to the zone of low significance of the variables in the model. Llob.: Llobregat; Card.: Cardona; Viladec.: Viladecavalls; RO: outlet of reverse osmosis; DWTP: outlet of drinking water treatment plant.

Figure 3

PCA (a) score plot and (b) loading plot obtained using the values of the variables from the electronic tongue. In the loading plot, the grey circle corresponds to the zone of low significance of the variables in the model. Llob.: Llobregat; Card.: Cardona; Viladec.: Viladecavalls; RO: outlet of reverse osmosis; DWTP: outlet of drinking water treatment plant.

Figure 3

PCA (a) score plot and (b) loading plot obtained using the values of the variables from the electronic tongue. In the loading plot, the grey circle corresponds to the zone of low significance of the variables in the model. Llob.: Llobregat; Card.: Cardona; Viladec.: Viladecavalls; RO: outlet of reverse osmosis; DWTP: outlet of drinking water treatment plant.

Figure 4

Bar graphs of (a) the hedonic evaluation (scoring the satisfaction upon tasting the samples on a scale from 1 (Dislike extremely) to 10 (Like extremely)), and (b) the ranking test (the samples are ranked from the first to the fifth, taking the preference as the only criterion) performed by the taste panel in comparison with the results obtained with the electronic tongue. Llob: Llobregat; Card: Cardona; RO: outlet of reverse osmosis; and DWTP: outlet of drinking water treatment plant.