SEC of simple polymers with molar mass detection in presence of instrumental broadening. Computer simulation study on the calculation of unbiased molecular weight distributions

This theoretical work presents a correction procedure for calculating an un biased MWD when analyzing a linear homopolymer by size exclusion chromatogr aphy with molar mass detection. The fractionation and the measurements are ideal, but the chromatograms are distorted by a nonuniform and skewed instr umental broadening (IB), and are contaminated with a zero-mean random noise . The main assumption is that the molecular weight calibration is linear in the chromatogram range. The following phenomenological procedure was proposed: (i) independently co rrect the mass- and molar mass chromatograms for IB through a robust invers e filtering technique; (ii) estimate the unbiased calibration from the rati o of the corrected chromatograms; (iii) adjust a straight line to the mid-v alues of that calibration; and (iv) estimate the unbiased MWD from the line ar calibration and the corrected mass chromatogram. For the chromatogram inversions, a minimum sized broadening matrix was sele cted and a singular value decomposition technique was applied. The followin g effects were evaluated: of an increased measurement noise, of uncertainti es in the range of the measured chromatograms, and of systematic errors in the IB function. The method fails for very narrow MWDs.