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GPC/MALS Analysis of NBS706 (KF-806, KD-806)

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It is known that elution of Polystyrene, PS using DMF eluent is later than that with THF eluent when organic SEC (GPC) columns packed with styrene-divinylbenzene polymer. Its separation was analyzed for THF and DMF eluents using Multi Angle Light Scattering (MALS) detector. NBS706, a linear type poly disperse Polystyrene standard, was used as a sample, which is supplied by the US National Bureau of Standard (NBS). Figure 1 shows the relationship between the RMS radius and the elution volume for each eluent. The elution with DMF eluent is rather late, but the correlation between the molecular size and the elution volume is good except for the small RMS area. In this area, separation of both eluents is done by GPC. The absolute molecular weights of NBS706 by GPC/MALS for both eluents are similar (286,000 by THF and 283,000 by DMF), the recovery rate by a RI detector is 100%, which means nothing was retained in the column. Fig. 2 is similar with Fig. 1, but its y-axis is molar mass. There is a big difference between the two eluents. This means that the GPC separation is performed by the molecular sizes, but not molar mass. Based on Fig. 1 and 2, the relationship between molar mass and RMS radius is shown in Fig. 3. Comparing molecules which have the same molar mass between DMF and THF, the RMS radius of molecules in DMF is smaller than that of THF due to shrinkages in DMF. Therefore, MALS enables the measurement of the absolute molecular weight and size, which can track the separation behavior and facilitate the evaluation.


Sample :
(1) 0.198% NBS706 in THF, 50μL
(2) 0.0935% NBS706 in 10mM LiBr in DMF, 100μL

 

Columns      : (1) Shodex GPC KF-806 (8.0mmI.D. x 300mm)
               (2) Shodex GPC KD-806 (8.0mmI.D. x 300mm)
Eluent       : (1) THF , (2) 10mM LiBr in DMF
Flow rate    : 1.0mL/min
Detector     : MALS + RI
Column temp. : 26°C

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