Instrumentation for Gel Electrophoresis

A power supply, an electrophoresis chamber with buffer reservoirs and a cooling thermostat are the major components required for gel electrophoresis (Fig. 3.6). The separation can be performed vertically or horizontally. 

The power supply delivers voltages of typically 200 to 500 V with electrical currents of 400 p,A to about 100 mA. The electrodes are dipped into the buffer reservoirs on each side of the gel. For most biomolecular separations, the pH is chosen such that the analytes are negatively charged. The analytes therefore migrate towards the anode. Hence, the electrode at which samples are introduced into the gel is chosen as the cathode, and the electrode at the other side of the gel is the anode. The whole instrument is encased in an insulating box to shield users from the high voltages. 

The electrophoresis chamber contains the gel matrix immersed in an electrolyte buffer. Vertical gels can be polymerised in a glass or perspex tube with 0.5 to 1 cm 

For vertical separations, the samples are dissolved in a glycerol or sucrose solution of high density to prevent them from mixing with the buffer in the upper reservoir. The sample wells in the slab gel are made during casting by using appropriate combs or formers. Due to the shape of the sample wells, the analytes move in the form of wide narrow bands. 

A thermostat is required for temperature control. Temperature controlled chambers ensure more reproducible separations as they help to dissipate heat from Joule heating (section 3.1.2) and protect sensitive analytes from thermal degradation. 

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