MULTIDETECTOR SIZE-EXCLUSION CHROMATOGRAPHY - A NOVEL-APPROACH TO CALIBRATION ELIMINATING LAG TIME-ESTIMATION

In order to obtain the correct calibration of molecular-weight sensitive detectors (such as on-line viscometers or light scattering detectors) in size-exclusion chromatography, it is necessary to account for the (molecular) non-uniformity of the calibration standards. This is true even in the case of the narrow molecular weight distribution standards typically commercially available for calibration. Methods of taking this non-uniformity into consideration are presented. For a multi-detector size-exclusion chromatography system calibrated in this way, independent calibration curves can be established for each detector. Thus, at a given hydrodynamic volume, corresponding signals from the different detectors can be obtained. This eliminates the need to estimate additional parameters such as interdetector volumes or lag times for matching signals from different detectors. The practicability of this approach in the analysis of (molecularly) nonuniform polymers is demonstrated by combining on-line viscometer and concentration signals (to obtain intrinsic viscosity versus molecular weight information) for two different polymers, viz. polystyrene and poly(methyl methacrylate). The resultant intrinsic viscosity versus molecular weight data is then compared to that predicted from the literature.