Polydispersity Study of Narrow Polystyrene Standards Using Light Scattering

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Abstract
Manufacturers of narrow polystyrene standards for use as column calibrants with size exclusion chromatography (SEC) often label the corresponding polydispersity (Mw/Mn) as < ∼1.05. These values appear to reflect more the errors associated with the measurement than the true narrow polydispersity. Ideally, we would measure polydispersity by a light scattering measurement of Mw and a membrane osmometry measurement of Mw. The ratio of such measurements would be expected to have an error on the order of 5%- a number comparable to the difference of the measured polydispersity and unity Multi-angle light scattering (MALS) allows the absolute determination of the rms radius independent of the separation technique and any other detector. Using this information and following the method of Shortt,1 column band broadening effects may be corrected and a far more precise determination of polydispersity made. A variety of standards from several manufacturers were measured, and the polydispersity of each was determined to be far smaller than stated, further confirming their suitability for column calibration purposes.