There are limits to electrophoretic techniques. Since passing current through a gel causes heating, gels may melt during electrophoresis. Electrophoresis is performed in buffer solutions to reduce pH changes due to the electric field, which is important because the charge of DNA and RNA depends on pH, but running for too long can exhaust the buffering capacity of the solution. There are also limitations in determining the molecular weight by SDS - PAGE, especially if you are trying to find the MW of an unknown protein. There are certain biological variables that are difficult or impossible to minimize and can affect the electrophoretic migration. Such factors include protein structure, post-translational modifications, and amino acid composition. For example, tropomyosin is an acidic protein that migrates abnormally on SDS - PAGE gels. This is because the acidic residues are repelled by the negatively charged SDS, leading to an inaccurate mass - to - charge ratio and migration. Further, different preparations of genetic material may not migrate consistently with each other, for morphological or other reasons.
in gel electrophoresis what is the purpose of the buffer
to reduce pH changes due to the electric field