1. Chapter 23
Potentiometry

2. Reference Electrodes
A reference is an electrode that has the half-cell potential known, constant, and completely insensitive to the composition of the solution under study. In conjunction with this reference is the indicator or working electrode, whose response depends upon the analyte concentration.

3. Reference Electrodes Ideal Reference Electrode:
Is reversible and obeys the Nernst equation
Exhibits a potential that is constant with time
Returns to its original potential after being subjected to small currents
Exhibits little hysteresis with temperature cycling

4. Reference Electrodes

5. Reference Electrodes
Calomel Electrodes:

6. Reference Electrodes
Silver/Silver Chloride Electrodes:

7. Metallic Indicator Electrodes
There are four types of metallic indicator electrodes:
Electrodes of the first kind.
Electrodes of the second kind.
Electrodes of the third kind.
Redox electrodes.

8. Metallic Indicator Electrodes

9. Membrane Indicator Electrodes
Properties:
Minimal solubility. A necessary property of an ion-selective medium is that its solubility in analyte solutions approaches zero.
Electrical conductivity. A membrane must exhibit some electrical conductivity, albeit small. Generally, this conduction takes the form of migration of singly charged ions within the membrane.
Selective reactivity with the analyte. A membrane or some species contained within the membrane matrix must be capable of selectively binding the analyte ion. Three types of binding:
Ion-exchange
Crystallization
Complexation

10. Membrane Indicator Electrodes
Glass Electrodes:

11. Membrane Indicator Electrodes
Glass Electrodes: Potential
The boundary potential.
The potential of the internal Ag/AgCl reference electrode.
A small asymmetry potential.

12. Membrane Indicator Electrodes
Alkaline Error
Selectivity Coefficients
Acid Error

13. Membrane Indicator Electrodes
Crystalline Membrane Electrodes:

14. Membrane Indicator Electrodes
Fluoride Electrode:

15. Membrane Indicator Electrodes
Liquid Membrane Electrodes:
Cation exchangers
Anion exchangers
Neutral macrocyclic compounds, which selectively complex certain cations

16. Membrane Indicator Electrodes

17. Ion-Selective Field-Effect Transistors (ISFETs)

18. Molecular-Selective Electrode Systems
Gas-Sensing Probes:
Microporous materials- manufactured from hydrophobic polymers that have a porosity of about 70% and a pore size of less than 1m, and are about 0.1mm thick.
Homogeneous films- solid polymeric substances through which the analyte gas passes by dissolving in the membrane, diffusing, and then desolvating into the internal solution. They are usually thinner than microporous in order to hasten the transfer of gas and thus the rate of response of the system.

19. Molecular-Selective Electrode Systems
Gas-Sensing Probes:

20. Instruments for Measuring Cell Potentials
Direct-Reading Instruments
Commercial Instruments
Utility
General-purpose
Expanded-scale
Research

21. Direct Potentiometric Measurements
The Sign Convention and Equations for Direct Potentiometry
The Electrode Calibration Method
Inherent Error in the Electrode
Activity Versus Concentration
Calibration Curves for Concentration Measurement
Standard Addition Method
Potentiometric pH Measurements with a Glass Electrodes
Summary of Errors Affecting pH Measurements with the Glass Electrode
The Operational Definition of pH

22. Potentiometric Titrations
Schematic representation of an automatic potentiometric titrator devised by Lingane in 1948.

23. References http://ull.chemistry.uakron.edu/analytical/Potentiometry/