PC-505B Manual, Rev. 201013
Warner
Instruments
A Harvard Apparatus Company
39
Reference electrodes
A reference electrode in the recording chamber maintains the bath at circuit ground
potential, the reference potential for all measurements. It is also the return path for currents
from the pipet electrode. A variety of Ag-AgCl reference electrodes are available from Warner
Instruments.
A simple reference electrode can be made from a silver wire. Use wire somewhat thicker than
the one in the pipet electrode holder. The end applied to the bath should be chlorided as
described on page 26 such that the Ag-AgCl coating can be submerged with no bare Ag exposed
to solution. The free end is connected to circuit ground.
Any exposed Ag surface that could potentially contact the bathing solution should be
insulated with a waterproof coating of epoxy cement, insulating varnish, or similar durable
waterproof coating. This precaution provides a stable baseline as long as the bath solution is not
changed.
When bath solutions are to be changed during an experiment, a KCl salt bridge can be used
to minimize changes in the junction potential that accompany these solution changes. A small
glass or plastic U tube filled with saturated or 3 M KCl in warmed 2% agar gel is usually employed
for this purpose. The AgCl reference electrode goes into one end of the tube and the other end is
applied to the bath.
