Rate of Migration

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The page below is a sample from the LabCE course Electrophoresis. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Rate of Migration

The net charge of a molecule is the most important factor affecting the mobility of that molecule. The greater the net charge, the greater the mobility or the more quickly the molecule migrates. The net charge of a particular compound depends upon the buffer and the resultant pH set by that buffer.
The size and shape of a molecule also influence the rate of migration in that the larger the size, the slower the molecule will move in electrophoresis.
The viscosity and the pore size in the support media or gels used for electrophoresis influence the rate of migration. Increased viscosity slows the migration, and increasing pore size speeds up the migration.
Increasing the strength of the electrical field by raising the voltage and increasing the temperature used for the electrophoresis will increase the mobility and rate of migration. When increasing these factors that affect mobility, caution is necessary. An increase in temperature could denature the sample and alter the characteristics of the support medium.
The ionic strength of the buffer and its effect on mobility is more complicated. The ionic strength of the buffer affects the thickness of the ionic cloud, the rate of migration, and the sharpness of the separated solutes. In electrophoresis, a cloud of ions forms over the medium and is composed of buffer ions, sample ions, and other nonbuffer ions. Increasing the buffer ionic strength increases the buffer ions in the cloud, slows the movement of solutes, and creates sharper bands. However, this also increases heat production.