Page 206 - Introduction to Colloid and Surface Chemistry

Charged in terfaces 195

Boundary
8
Buffer Protein
1
solution— * ^ — solution
I
^
V 1 Horizontal
Boundary
1
cross-section

Figure 7.8 A Tiselius electrophoresis cell

assembly is immersed in a thermostat. On attaining hydrostatic and
thermal equilibrium, the sections of the cell are slid into alignment to
form two sharp boundaries. A current is passed through the cell, and
the migration of the boundaries is usually followed by a schlieren
technique which shows the boundaries as peaks.
The elongated rectangular cross-section of the cell provides a
reasonably long optical path for recording the boundary positions,
and at the same time permits efficient thermostatting. By working at
around 0-4°C (at which aqueous solutions have maximum density
and dp/dT is small), convectional disturbance of the boundaries due
to the heating effect of the applied current can be minimised even
further. The density difference at the boundaries is usually sufficient
to prevent disturbance due to electro-osmotic flow at the cell walls.

Albumin

Figure 7.9 Electrophoretic diagram (ascending) for human blood serum