10-08-2012, 11:21 AM
Electrical conductivity of Electrodes and Recording Electrodes
[attachment=30889]
Electrode – Electrolyte Interface
a) If electrode has same material as cation, then this material gets oxidized and enters the electrolyte as a cation and electrons remain at the electrode and flow in the external circuit.
b) If anion can be oxidized at the electrode to form a neutral atom, one or two electrons are given to the electrode.
Half Cell Potential
A characteristic potential difference established by the electrode and its surrounding electrolyte which depends on the metal, concentration of ions in solution and temperature (and some second order factors) .
The half cell potential of the standard hydrogen electrode has been arbitrarily set to zero. Other half cell potentials are expressed as a potential difference with this electrode.
Reason for Half Cell Potential : Charge Separation at Interface
Oxidation or reduction reactions at the electrode-electrolyte interface lead to a double-charge layer, similar to that which exists along electrically active biological cell membranes.
Motion Artifact
Why
When the electrode moves with respect to the electrolyte, the distribution of the double layer of charge on polarizable electrode interface changes. This changes the half cell potential temporarily.
What
If a pair of electrodes is in an electrolyte and one moves with respect to the other, a potential difference appears across the electrodes known as the motion artifact. This is a source of noise and interference in biopotential measurements
Microelectrodes
Why
Measure potential difference across cell membrane
Requirements
Small enough to be placed into cell
Strong enough to penetrate cell membrane
Typical tip diameter: 0.05 – 10 microns
Types
Solid metal -> Tungsten microelectrodes
Supported metal (metal contained within/outside glass needle)
Glass micropipette -> with Ag-AgCl electrode metal
[attachment=30889]
Electrode – Electrolyte Interface
a) If electrode has same material as cation, then this material gets oxidized and enters the electrolyte as a cation and electrons remain at the electrode and flow in the external circuit.
b) If anion can be oxidized at the electrode to form a neutral atom, one or two electrons are given to the electrode.
Half Cell Potential
A characteristic potential difference established by the electrode and its surrounding electrolyte which depends on the metal, concentration of ions in solution and temperature (and some second order factors) .
The half cell potential of the standard hydrogen electrode has been arbitrarily set to zero. Other half cell potentials are expressed as a potential difference with this electrode.
Reason for Half Cell Potential : Charge Separation at Interface
Oxidation or reduction reactions at the electrode-electrolyte interface lead to a double-charge layer, similar to that which exists along electrically active biological cell membranes.
Motion Artifact
Why
When the electrode moves with respect to the electrolyte, the distribution of the double layer of charge on polarizable electrode interface changes. This changes the half cell potential temporarily.
What
If a pair of electrodes is in an electrolyte and one moves with respect to the other, a potential difference appears across the electrodes known as the motion artifact. This is a source of noise and interference in biopotential measurements
Microelectrodes
Why
Measure potential difference across cell membrane
Requirements
Small enough to be placed into cell
Strong enough to penetrate cell membrane
Typical tip diameter: 0.05 – 10 microns
Types
Solid metal -> Tungsten microelectrodes
Supported metal (metal contained within/outside glass needle)
Glass micropipette -> with Ag-AgCl electrode metal