Electroanalytical chemistry techniques can determine the concentration, stoichiometry, and activity of chemical species using electrical properties. Potentiometry specifically measures electrode potentials to analyze ion concentrations. Reference electrodes have a constant potential and are unaffected by the analyte composition, allowing measurement of a cell potential relative to the reference. Ion-selective electrodes convert specific ion activity into a measurable potential via selective membranes based on ion exchange, crystallization, or complexation.

1. Electro analysis…
Potentiometry..
By
Vishaalini kamali.R
Biotech 2 year

2. ELECTRO ANALYTICAL
CHEMISTRY….
• Consists of group of quantitative methods of
analysis
• It uses the electrical properties of the analyte to
determine
1.the concentration of each of the
chemical species (unlike other techniques that can
only find – the total conc)
2.stochiometry of the sample
3.rate of charge transfer or mass
transfer
4.extent of adsorption or
chemisorption
5. rates and equi constants

3. advantages
• Allows to find the conc of each chemical
species than as a whole
• Most important: it can find the activity
of ions unlike others…(activity is more
important than the conc)
• The cost is low compared to other
spectroscopic instruments

4. Electrochemical cells
• It is a device capable of either
generating the electrical energy from
the chemical reactions or vice versa
• Consists of electrodes, electrolyte,
power supply, voltmeter, wattmeter,
salt bridge.

7. Potentials in electrochemical cell…
• The potential of the cell depend upon
the activity of the reactants and
products and indirectly to their molar
concentrations

8. what is activity???
• Measure of the effective conc of the
species in a mixture
• Dimensionless quantity
• Depends on temp, pressure, standard
state of species and conc

9. What is standard state?
• It is a reference point used to
calculate the properties of the
materials under different conditions.
• The standard potential is equal to the
cell potential when the activity is unity,
ie, when a=1, then Ecell= E°cell

10. Potentiometry..
• Methods of analysis based on the
measurement of potential of electrode
system
• consists of two electrodes called
reference and indicator electrode,
potentiometer and a solution of analyte
• enable selective detection of ions in
presence of other substances.

11. Reference electrodes
• Highly desirable: to know the half cell
potential of one electrode
• Thus the electrode whose half cell
potential is- constant and completely
insensitive to the composition of
analyte under study- reference
electrode

12. Ideal reference electrode..
• Reversible and always obeys nerst eqn
• Exhibits a constant potential
• Returns to original potential after being
subjected to small currents

15. Ion selective electrodes..
• The membrane electrodes- allow rapid
and selective determination of numerous
cations and anions by direct
potentiometric measurements
• Also known as specific ion electrode
• Converts the activity of a specific ion
dissolved in the solution into an electric
potential that can be measured by
voltmeter

16. Properties..
Properties:
• Minimal solubility.
• Electrical conductivity.
• 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

17. Types of ion selective membrane
electrodes…
• Crystalline: 1.single (ex:LaF3 for f-)
2. polycrystalline (ex:Ag2S
. for
Ag+)
• Non crystalline: 1. glass (ex: silicate
glasses for Na+ and H+)
• 2.liquid: (ex: liq ion
exchanger for Ca2+ and K+)
• 3.immolized liquid in a
rigid polymer ( ex: PVC matrix for Ca2+
and NO3-)

19. Molecular selective electrodes….
• These are selective towards certain of
molecules
• Two types:
• 1. for determination of dissolved gasses
• 2. determination of organic compounds
like glucose and urea

20. Gas sensing probes…
• An indicating electrode is first placed
into a specific solution
• On the opposite side there is a
permeable membre
• When the solution containing Co2 is
brought into contact with the porous
membrane, it passes through and
equilibrium is established

21. • in the internal medium another
equilibrium is established
• This causes change in the pH of the
internal medium to change and the glass
electrode immersed in the film of
internal solution detects this pH change

23. Biocatalytic membrane electrodes…
• Used to determine the compunds of
biological interest
• It combines the selectivity of enzyme
catalysed reactions with
electrochemical transducers

24. Mechanism..
• When the sample is brought into
contact with an immoblized enzyme, the
analyte undergoes a catalytic reaction
to yield species like ammonia, Co2, H+
ions,or H2O2
• The conc of this product is directly
proportional to the analyte conc that is
determined by the transducer

25. Instruments…
• Direct-Reading Instruments
• Commercial Instruments
– Utility
– General-purpose
– Expanded-scale
– Research

26. Potentiometer
• Instrument used to measure the EMF,
TPD, internal resistance of a cell.
• It consists of a board where a tungsten
or manganese wire is fitted on it
• Driving cell (E) of some EMF which is
always greater than the EMF (E’) to be
measured is used to send current
through the circuit

29. Principle and working..
• Generally when the cells of same emf if
connected to the galvanometer shows
zero deflection
• But if emfs vary then deflection is
observed
• the potential dropped between two
points in a wire of uniform cross section
is directly proportional to the distance
between the points