Band Broadening in Size Exclusion Chromatography of Polymers. State of the Art and Some Novel Solutions. 25th Anniversary Issue

Abstract

This work reviews the main problems of band broadening (BB) in SEC, and also presents some novel and state-of-the-art solutions. The first part of the work describes Tung´s equation and presents an overview on the expected order-of-magnitude of BB effects. The second part deals with the experimental determination of the broadening function using ultra-narrow standards. The third part describes several algorithms for inverting the mass chromatograms. To allow for the simultaneous occurrence of narrow and broad regions in the same chromatogram, a novel regularization filter with a position-dependent parameter was introduced. When comparing different inversion procedures, the maximum entropy method has proven effective for recuperating structural details narrower than two times the width of the kernel. For broader and smoother regions, most other inversion procedures are equally effective. The fourth part of the work aims at producing unbiased estimates in multidetection SEC. For a derived variable obtained by linear combination of two or more chromatograms, it is preferable to directly perform the calculation from the raw measurements, and then to correct the (broadened) derived variable with the standard system kernel. When estimating molar masses from in-line molar mass sensors, intolerable errors are produced near to the baselines. To cope with this problem and to simultaneously correct for BB, a theoretical procedure is reviewed that is based on recuperating the linear (unbiased) molecular weight calibration.