CAMLPR Chemistry Practice Test

Size exclusion chromatography separates components by molecular size (their hydrodynamic volume or Stokes radius). The column uses porous beads: large molecules can’t enter the pores and are excluded from the interior, so they take a shorter, more direct path through the column and elute first. Smaller molecules can enter many pores, taking a longer, more tortuous route, and thus elute later. Because retention depends on how easily a molecule can access the pore network, not on solubility, polarity, or charge, this method sorts mixtures by size rather than by these other properties. This is why the technique is often called gel filtration, and columns are calibrated to relate elution volume to molecular size.