Poly(Vinylpyrrolidone) (4) (DMF Eluent: Effect of LiBr Concentration)

In the case of polymers which have ionic functional groups, the ionic functional groups repel each other and/or aggregation take place, and therefore, the apparent molecular size of the polymers become large. When analyzing such polymers by a organic SEC (GPC) column (GPC KD-806M) with DMF as the eluent, elution time may be very fast and/or abnormal peak shape may be obtained. To prevent such ionic dissociation, the addition of salts such as LiBr is know to be effective. Although the optimal concentration of LiBr is considered to be around 10mM, no systematic study on this point has been performed. Here, the result of the study to determine the optimal concentration range of LiBr in DMF is shown for polyvinylpyrrolidone. It is confirmed that the concentration of 10mM which has been used traditionaly is in the range of optimal concentration range. In the figure, chromatograms show the output from RI detector and "x" marks show the output from MALS (multi angle laser light scattering) detector. The table shows the calculation result from the data of MALS detector. As you can see from the table and figure, larger molecular weight and larger molecular size components are mesured when the LiBr concentration is 0 to 0.001mM compared with the case when the LiBr concentration is 0.5 to 50mM. 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.



LiBr conc. Mw(x104) Mn(x104) Rw(nm) Rz(nm)
0mM
(750)
(297)
(222)
(371)
0.001mM
(220)
(132)
(243)
(259)
0.01mM
95.6
54.1
67.3
92.0
0.1mM
78.2
36.2
48.9
58.9
0.5mM
78.5
32.5
48.3
56.7
1mM
79.0
25.5
40.0
56.8
10mM
79.2
29.2
44.7
56.8
50mM
78.9
23.4
37.2
56.8

Sample : 0.01% PVP, Poly(vinylpyrrolidone), 100micro-L

Column       : Shodex GPC KD-806M (8.0mmID*300mm)
Eluent       : LiBr in DMF
Flow rate    : 1.0mL/min
Detector     : Shodex RI, MALS
Column temp. : 40deg-C