Lecture 15 Electrochemical sensors II

Also, the equilibrium reaction can be quantified by salt-partitioning constant, Kp, as defined by
Thus, the concentration of the aqueous anion in the cation-selective membrane doped with anionic sites is negligible in the charge balance in the membrane phase [I+]M = [R-]M + [X-]M ⇌ [R-]M selectivity of anion-exchanger-based ISEs follows 16 > F ClO4- > SCN- > I- > NO3- >Br- > Cl- > HCO3- > SO42-
L. C. Clark Jr., Trans. Am. Soc. Artif. Intern. Organs, 1956, 2, 41
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4. Modified electrodes
A. Chemical modification {chemical bonding).
B. Adsorption C. Electroadsorption D. Plasma(等离子体)
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Vequiv.
C. Amperometric titrations with double hydrodynamic electrode
Idet generator A±n1e →B solution B+X → products Detector B±n2e → C (or A) N’= 0.035
Applied Electrochemistry
Dept. Chem. & Chem. Eng. 1
Lecture 14
Electrochemical sensors
Dept. Chem. & Chem. Eng. 2
Outline
1ቤተ መጻሕፍቲ ባይዱ
2 3 Introduction Potentiometric sensors Amperometric sensors Voltametric sensors
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(4) Charged-ionophore-based ISEs
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Outline
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2 3 Introduction Potentiometric sensors Amperometric sensors Voltametric sensors
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1. Introduction
When the information is obtained from measurement of current, that is in amperometric sensors, the role of the Ohm’s Law becomes immediately apparent.
c. Reduction/oxidation of the species that was accumulated at the electrode
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An example of biochemical sensor
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Electrochemical sensors
Electrochemical sensors is a subclass of chemical sensors in which electrode is used as a transduction elements
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Outline
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2 3 Introduction Potentiometric sensors Amperometric sensors Voltametric sensors
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Miniaturization of potentiometric sensors. (A) Conventional ion-selective electrode (ISE) with reference electrode connected to the field-effect transistor amplifier. (B) The electrical connection between ISE and the amplifier is made shorter. (C) Electrical connection is eliminated and the ISE membrane is placed directly at the input of the amplifier, thus forming an ISFET (D)
unique for the analyte
Charge
activity in the sample solution of analyte I
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Schematic view of the equilibrium between sample
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Classification and Mechanism (1) Phase boundary potential izi (membrane) ⇌ izi (sample) Under equilibrium conditions
(3) Neutral-ionophore-based ISEs I+(Membrane) + L(membrane) ⇌ IL+(membrane) The formation constant, , is given by = aILM/(aIM aLM) the charge balance in the membrane phase RT = [I+]M + [IL+]M ⇌ [IL+]M [L]M = LT - [IL+]M ⇌ LT - RT aIL = ILM RT/ LM(LT - RT)
Forms of amperometric titration
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B. Biamperometric titration R1 + O2 ⇌ O1 + R2 I i ii iii
Two redox electrodes Non-reference electrode App: a reversible system before or after the endpoint i Both 1 and 2 are rev. ii only 2 is rev. iii only 1 is rev. V
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Examples of modifiers for amperometric sensors
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Bard and Faulkner, 2001, pp. 584–585
Processes that can occur at a modified electrode. (1) heterogeneous reduction process; (2) successive transfer of electron between reduced molecules Q (5), until the transfer to A at the surface (3); (4) diffusion of A into the film and its reaction with Q; (6) direct penetration of A through the pinhole to the substrate electrode
Conceptual drawing of three electrode amperometric electrochemical sensor and potentiostat
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2. Amperometric titrations
A. Simple amperometric titration i I ii iii Vequiv iv V Two electrodes: a redox indicator electrode & a reference electrode A fixed potential difference
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5. Increase in sensitivity: pre-concentration techniques principle a. application of a pulse waveform and a.c. voltammetry b. utilization of a pre-concentration step that accumulates the electroactive species on the electrode surface i = nFAvA process a. Deposition or adsorption of the species on the electrode b. Change to an inert electrolyte medium
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Contruction of chemical sensors
A transduction element covered with chemical or biochemical recognition layer Target analyte interact with the recognition layer and change the resulting from interactions to electrical signals
Membrane compositions and selectivity coefficients of ion-exchanger-based ISEs