I know it separates compounds based on size, but I don’t understand what the numbers can tell you and what situations GPC is ideal for. And do the numbers represent molecular weight, or what are they supposed to tell you?
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My understanding as a basic chemistry student is:
GPC consists of a porous gel medium that is combined with a solvent. The compound(s) to be tested/separated are dissolved in the solvent at one end of the gel medium and allowed to diffuse to the other side, with a chance to be absorbed into and retained by the pores of the gel. Depending on a compound’s size as compared to the pore’s size, it may be absorbed by the gel, slowing or even halting its progress to the other side. If the compound is completely absorbed, then it is “retained” by the gel. Basically, the smaller a compound’s molecular size, the longer it should take to move through the gel/solvent medium, if it makes it through at all, and this time is related to the intrinsic viscosity of the compound.
GPC should tell you the intrinsic viscosity of the compound by measuring the time the volume of compound takes to move through the gel/solvent, which for polymers, you can use to find the Molar Mass of the compound due to the Mark–Houwink equation, and from there you can find the molecular formula provided you know the empirical formula.
GPC is nice for quickly/easily separating out various compounds by using specific gel pore sizes, and for finding the molar mass of a polymer as a function of intrinsic viscosity, but it only works to separate compounds of differing molar masses and it needs some filtration which can throw the results off a bit.
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