Ionic functional groups found on polymers repel each other and/or aggregation take place, and therefore, the apparent molecular size of the polymers seems larger than actual. When analyzing such polymers by a organic SEC column (GPC KD-806M) with DMF as the eluent, the peak may elute early and/or abnormal peak shape may be obtained. The addition of salts such as LiBr is know to be effective for preventing ionic dissociation. Although the optimal concentration of LiBr is considered to be around 10 mM, no systematic study has been performed. The following study was used to determine the optimal concentration range of LiBr in DMF for polyvinylpyrrolidone. It is confirmed that the concentration of 10 mM which has been used traditionaly is in the range of optimal concentration range. The chromatograms show the output from RI detector and "x" marks show the output from MALS (multi angle light scattering) detector. The table shows the calculation result from the data of MALS detector. The inaccurate molecular weight and larger molecular size components are mesured when the LiBr concentration is low from 0 to 0.001 mM compared with the case when the LiBr concentration is higher from 0.5 to 50 mM. From the result, we can say that apparent large molecular weight components exist because of ion repellent within the polymer, electrostatic with column packing material and aggregation of the polymers when LiBr concentration is not enough.
Please refer to the case of cellulose acetate.

Sample: 100 μL
0.01 % Polyvinylpyrrolidone