2D gel electrophoresis

It is a powerful method of separating protein along a tubular gel using iso-electric focusing and sodium dodecyl sulphate polyacrylamide gel. The sample undergoes iso-electric focusing first; producing first dimension. The sample is then placed horizontally on top of SDS-PAGE and spreads across. The sample then moves vertically down again to yield the second dimension;producing a 2D pattern. So the sample has been separated by virtue of Iso-electric point (pI), when they move horizontally and by virtue of their size; when they move down vertically.