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Electrochemical Sensors James J. Noe¨l and Gurinder Kaur Ahluwalia

Measurement set-up for the electrochemical characterization of the chalcogenide glass-based thin-film sensor array

J.J. Noe¨l, Ph.D. (*) Department of Chemistry, The University of Western Ontario, 1151 Richmond St., London, N6A 5B7, ON, Canada e-mail: [email protected] G.K. Ahluwalia, Ph.D. Materials and Nanotechnology Research Laboratory, Department of Physics College of The North Atlantic, Labrador West Campus, 1600 Nichols Adam Highway, Labrador City, A2V 0B8, NL, Canada e-mail: [email protected] © Springer International Publishing Switzerland 2017 G.K. Ahluwalia (ed.), Applications of Chalcogenides: S, Se, and Te, DOI 10.1007/978-3-319-41190-3_6

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J.J. Noe¨l and G.K. Ahluwalia

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6.1

Introduction

Potentiometric sensor electrodes constitute a class of chemical sensors that can indicate the presence and quantity of a species of interest (the analyte), based on the electrochemical response that the analyte stimulates on the sensor. Whereas some other types of electrochemical sensors rely on a change in the electrolytic current (amperometric sensors) or charge (coulometric sensors) to sense and quantify the analyte, potentiometric sensors generate a certain electrochemical potential difference in response to the presence of a specific analyte, and that potential difference is related quantitatively to the abundance of that species. This chapter begins with a summary of the principles underlying the function of potentiometric sensors in general, and a description of analytical approaches employing them, before turning to focus on sensors employing chalcogencontaining compounds, especially ISE based on chalcogenide glass membranes, and briefly mentioning some future trends in the field.

6.2 6.2.1

ISE Principles and Theory Sensor Response and the Phase Boundary Potential

A chemical sensor is a transducer that converts some chemical information into an electrical signal that can be detected by an appropriate instrument and reported to a user. In the case of potentiometric sensors, the chemical information transduced by the sensor is the concentration or, more precisely, the activity of a chemical species. This transduction is effected via the influence of the chemical activity of the species of interest on the position of a phase boundary equilibrium involving that species, which is indicated by the electrochemical potential that develops between the sensor and a reference electrode included for the purpose of making the measurement (Fig. 6.1). The potentiometric response of the sensor can be described quantitatively, according to equilibrium thermodynamic theory, beginning with the concept of the electrochemical potential, μ. For analyte species, A, in phase p, μAp ¼ μAp  þ RT lnaAp þ zA Fφp

ð6:1Þ

where μAp is the electrochemical potential of ion or molecule A in phase p, μAp  the standard chemical potential of ion or molecule A in phase p, R the universal gas constant, T the absolute temperature, aAp the activity of species A in p