The net charge of a molecule is the most critical factor affecting its mobility. 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 migration rate: the larger the size, the slower the molecule will move in electrophoresis.
The viscosity and pore size of the support media or gels used for electrophoresis influences the migration rate. Increased viscosity slows the migration, and increasing pore size speeds it up.
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 these factors 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 migration rate, and the separated solutes' sharpness. In electrophoresis, a cloud of ions forms over the medium and comprises a buffer, sample, 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.