Polystyrene narrow standards, effect

The molecular-weight distributions were measured using a Waters GPC in the dual-detector mode (DRI and UV). The UV detector was operated at 254 nm. The samples were prepared by dissolving 2 mg of polymer in 10 ml of THE The injection volume was 200 pi. Separations were effected using two Polymer Labs 10-gm PL mixed-B columns. THF was used as the mobile phase. The molecular-weight distributions were calculated relative to narrow polystyrene standards ranging from 102 to 4 x 106 M ,... 

Figure 1. The calibration relation M(Vp) and effective relations M (v) of narrow MWD polystyrene standards.

Fig. 2. Effect of the uv detector noise on the estimation of the molecular weight as function of elution volume for a narrow polystyrene standard. The symbols represent molecular weights obtained using the universal calibration and viscosity measurements on collected fractions...

Since the calibration of a GPC is dependent upon the effective size in solution of the sample molecules, the type (structure) of molecules used for the calibration is important. The ideal case is to calibrate with a standard sample(s) of the material of interest. However, this is not always possible. In those instances, arbitrary standards are chosen. The arbitrary standards are used to construct a size calibration where the molecular size is calculated from the standard. For polymer analysis, these standards are often polystyrene of narrow molecular weight distribution. These standards may be purchased from a variety of suppliers. 

The SEC columns were calibrated using narrow molecular weight distribution water soluble polymer standards sodium polystyrene sulfonate, NaPSS (Pressure Chemical Company, Pittsburgh, PA) and dextrans (Pharmacia Fine Chemicals, Piscataway, NJ). The universal calibration curve proposed by Grubisic et al. (13) was found not to be applicable for these polymer standards. The alternative calibration procedure of Coll and Prusinowski (J ) which incorporates excluded volume effects in the numerical value of the Flory parameter was found to be applicable for this system ( ). The calibration curve for the two-column network system described above is shown in Figure 3. The Kyyy parameter used on the abscissa of Figure 3 is a normalized elution volume parameter defined by Equation 1,... 

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