I know that DNA molecules or proteins can be separated in electrophoresis because the electrical charge is used to pull the DNA through the gel. So instead of using electrical, can I using physical impact like pumping ?
If you tried to set up a system in which movement of DNA molecules through a gel matrix was driven by pumping buffer, the gel would become compressed. I am old enough to remember running vertical agarose gel electrophoresis overnight, and these gels would collapse under normal pressure to about 2/3rds of their initial height. A gel porous enough to give useful separation of DNA molecules just isn't strong enough to withstand pumping.
not from gels but physical force can be used to separate molecules.. e.g. density centrifugation, filtration. Closest to what you are asking is size exclusion chromatography in HPLC where molecules are separated based on size and high pressure is maintained in order to pump the solution (containing the analytes) through the stationary phase.
As Alan Boyd mentioned, the gels cannot withstand high pressure. In HPLC silica beads are used (sometimes coated with specific resins for e.g. in ion-exchange chromatography).
The principal differences between electrophoresis and HPLC (chromatogrphy) are:
- HPLC relies on differential interaction of the molecules with the stationary phase (i.e beads) whereas electrophoresis is purely based on the hydrodynamic size of the molecules.
- HPLC uses pressure to keep the entire mobile phase (solution) pumping through the stationary phase, whereas electrophoresis uses electric field to move the molecules.
- HPLC can also be used for uncharged molecules
Size exclusion and gel-filtration chromatographies resolve the molecules based on size as in the case of electrophoresis but as I previously mentioned, the molecules need not be charged. The techniques used for analysis of molecules in both techniques can be similar. For e.g UV absorption/fluorescence. An advantage of HPLC is that it can be connected to other analyzers like Mass Spectrometer, Flame Photometer etc.