The Microscope Method of Electrophoresis

 

This method of electrophoresis is only effective for examining the mobilities of fairly large particle such as blood cells, clay particles and certain micro-organisms. The particles are suspended in a buffer solution that is situated in the electric field and are directly observed by a microscope. The apparatus is simple and consists of a suitable cell into which a microscope that can be focussed and includes electrodes and an appropriate power supply. A number of different types of cell have been used, both flat cells and cylindrical cells and they can be oriented vertically or horizontally. In mounting the cell, it is essential that any convective liquid flow other than that induced by the electric field is completely eliminated. The use of small currents and thermal shields can reduce thermal convection. An example of the Abramson cell is shown in figure 3.

Figure 3. The Abramson Cell

 

It is essential to avoid any convective flow that does not arise from electrophoresis. Thermal convection can be avoided or minimized by using heat filters and low electrophoretic currents. The measurements can be difficult due to electro-osmotic flow that arises from the charges on the glass surfaces. Hydrodynamic theory predicts that the flat cell of the type described by Abranson can only be operated where osmotic flow is reduced to zero at positions of 0.21 and 0.79 of the cell thickness. Consequently, measurements must be taken at these levels. Today, microscope techniques are not widely used and their application is confined largely to the determination of the isoelectric points and mobilities of a range of micro organisms and the cellular components of blood. The elctrophoretic mobility of the red blood cells of animals within a species is constant but varies significantly between species.