1. Electroanalysis
measure the variation of an electrical parameter (potential, current, charge, conductivity) and relate this to a chemical parameter (the analyte concentration)
Selectivity: by choice of operating parameters (potential, current etc…) and/or the electrode material
applications
environmental analyses
quality control
biomedical analyses etc

2. Fundamentals
Redox reactions

3. Electrochemical Cells
galvanic:
spontaneous chemical reactions to produce
electrical energy (ΔG = -nFE, negative)
applications: batteries, potentiometry (pH, ISE)
electrolytic:
utilisation of energy (ex: applied V) to force a chemical rxn to take place (ΔG +)
applications: coulometry, voltammetry

4. Galvanic Cells line notation (shorthand)
| interface between two phases. || salt bridge
Cd(s) | CdCl2(aq, M) || AgNO3(aq, M) | Ag(s)

5. Half-Reactions
Ecell= Ecathode (+) - Eanode(-)

6. Standard Potentials
To predict the reactivity of oxidants or reductants we need to measure the potential of each half-reaction.
impossible!!....for every oxidation we have a reduction reaction
Define a standard half-cell of potential = 0V against which all other half-cell reduction potentials are measured (with the std half-cell attached to the negative terminal of the potentiometer). Each component in these standard cells having unit activity (pressure, conc.)

7. Standard Hydrogen Electrode
Pt(s) | H2(g, A=1) | H+(aq, A=1) || Ag+(ag, A=1)
|_________________________|
NHE
H+(aq, A=1) + e-  1/2H2(g, A=1) E0=0 V

8. Electrochemical Series
Reduction half-reactions
oxidant reducing agent E0 (V)
stronger oxidant
F2(g) + 2e-  2F
Ce4+ + e-  Ce
Ag+ + e-  Ag(s)
Fe3+ + e-  Fe
O2 + 2H+ + 2e-  H2O
Cu2+ + 2e-  Cu(s)
2H+ + 2e-  H2(g)
Cd2+ + 2e-  Cd(s)
Zn2+ + 2e-  Zn(s)
K+ + e-  K(s)
Li+ +e-  Li(s)
stronger reducer

9. Nernst Equation for a half-rxn aOx + ne-  bRed
R= gas constant T= temperature in Kelvin
n= no. of electrons in half-rxn
F= Faraday constant (96485 C/mol)
A= activity (= 1 for a pure solid, liquid or solvent and expressed in mol/L for solutes and in bar for gases)

10. Converting ln to log10 (x 2,303) and at 25oC (298.15K)
Nernst Equation
Converting ln to log10 (x 2,303) and at 25oC (298.15K)

11. Potentiometry
the measure of the cell potential to yield chemical information (conc., activity, charge)
Measure difference in potential
between two electrodes:
reference electrode (E constant)
indicator electrode (signal α analyte)

12. Reference electrodes
Ag/AgCl:
Ag(s) | AgCl (s) | Cl-(aq) || .....

13. Reference Electrodes SCE:
Pt(s) | Hg(l) | Hg2Cl2 (l) | KCl(aq., sat.) ||.....

14. Indicator Electrodes Inert:
Pt, Au, Carbon. Don’t participate in the reaction.
example: SCE || Fe3+, Fe2+(aq) | Pt(s)
Certain metallic electrodes: detect their ions
(Hg, Cu, Zn, Cd, Ag)
example SCE || Ag+(aq) | Ag(s)
Ag+ + e-  Ag(s) E0+= 0.799V
Hg2Cl2 + 2e-  2Hg(l) + 2Cl- E0-= 0.241V
E = log [Ag+] V

15. Ion selective electrodes (ISEs)
A difference in the activity of an ion on either side of a selective membrane results in a thermodynamic potential difference being created across that membrane

16. ISEs

17. Combination glass pH Electrode

18. Combination glass pH Electrode
β~ 1, constant = asymmetric potential (2 sides are not identical)

19. Other ISEs
by changing the composition of the glass, ISE selective for different ions can be fabricated
By replacing the glass with a perm-selective barrier incorporating a selective binding agent (ion-exchanger, host, doped crystal) ISEs for different ions can be fabricated

20. Voltammetry
The measurement of variations in current produced by variations of the potential applied to a working electrode
polarography:
Heyrovsky (1922): first voltammetry experiments using a dropping mercury working electrode
In voltammetry, once the applied potential is sufficiently negative, electron transfer occurs between the electrode and the electroactive species: Cu2+ + 2e → Cu(Hg)
Hg  liquid metal (surface can be renewed)

21. electron transfer to the electroactive species.
The polarogram
points a to b
I = E/R
points b to c
electron transfer to the electroactive species.
I(reduction) depends on the no. of moecules reduced/s: this rises as a function of E
points c to d
when E is sufficiently negative, every molecule that reaches the electrode surface is reduced.

22. Reactions that can be studied using voltammetry
amalgam-forming metallics;
reducible metallic ions e.g. Fe(III) → Fe(II);
reducible anions e.g. chromate, iodate...
reduction of molecular oxidants e.g. NO2, O2, H2O2...
reduction of organics, e.g. ketones, quinones, aldehydes, peroxides...

23. Glucose Monitoring and Diabetes
Diabetes is a serious disease, and, with its complications, is the fourth leading cause of death by disease in the United States. Its causes are unknown, and there is no cure.
Testing: A Crucial Tool
Blood tests, done by pricking the finger for a drop of blood, are recommended by most doctors because they give the exact amount of blood sugar at any given moment.
There are an estimated 14 million diabetics in the U.S.
It is recommended to test blood glucose levels at least 4 times daily.
Market of 56 millions disposable tests per day!!

24. Voltammetric Blood Glucose Monitors
An example of a test is the use of the immobilised enzyme glucose oxidase, which releases electrons on interaction with glucose. A sensor of this type could detect the level of glucose in the blood.

25. Glucose Biosensors Glucose + O2 Gluconic acid + H2O2
Glucose + mediator(ox) Gluconic acid + mediator(red)