Chromatography involves separating out a mixture, typically by passing it through a separation medium that gradually traps solutes due to their size – in Gel permeation chromatography (GPC) a sample is dissolved in suitable solvent and passed through a gel-based separation medium. This could be done immediately ahead of analysis step, perhaps to see how much of a specific protein is within a sample, or it could be done to synthesise a highly purified material for later fabrication steps.