There are several factors to take into account when you use GPC method to determine the Mw of polymers. The first one is the molecular weight and the Molecular Weight Distribution of the standards. The conformation of Pullulan, Dextran and PS-OBG is different. The conformation of Pullulan and Dextran is similar to Globular coil in water while the conformation of PS-OBG standards are expanded flexible chains.
Secondly, because of this conformation difference, the hydrodynamics volume will not be the same what will lead to a distinctive elution time.
Nowadays, a wider range of industries are using polymers like hyaluronic acid, chitosan, carboxymethyl cellulose, fungal polysaccharide. The conformation of this type of polymers is similar to the one of PS-OBG. So, if you use Pullulan or Dextran to determine the Molecular Weight of these, it can lead to significant overestimation of Molecular Weight. Oat beta-glucan standards can better reflect the genuine molecular weight of these polysaccharides.
.