AN EXTRAPOLATION METHOD FOR ELIMINATING OVERLOAD EFFECTS FROM GEL PERMEATION CHROMATOGRAMS

For high polymers eluted through a gel permeation chromatograph by tetrahydrofuran at 50°C and by Tetralin at 130° to 145°C the level of distortion of a chromatogram decreases as the weight of polymer injected into the gel permeation chromatograph decreases. The effect is present down to injected weights of 44 microgrammes. Comparing single chromatograms of polymers of different molecular weight by injecting constant weight may be misleading because the level of distortion of the chromatogram also decreases as the molecular weight of the polymer decreases. A method to eliminate distortion due to finite injected weight by extrapolating data to zero injected weight has been developed for polystyrenes eluted by tetrahydrofuran. This method gives viscosity average molecular weights which agree with intrinsic viscosity measurements. The systematic and random errors in the calculation of average molecular weights from a single chromatogram and hence the errors in the extrapolation method are examined. The major random error stems from uncertainty in the chromatograph baseline. The size of this error first depends on the level of instrumental noise and drift and secondly depends strongly on the shape of the distribution. © 1969.