<P> 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 . </P>
in gel electrophoresis what is the purpose of the buffer
to reduce pH changes due to the electric field