Size Exclusion Chromatography Calibration Assessment Utilizing Coupled Molecular Weight Detectors

Abstract

This paper shows that the usual method of representing an SEC calibration curve by a single polynomial curve may often be inadequate with new high resolution columns. Data points wind about the fitted line. The significant magnitude and systematic nature of these deviations clearly appear when a plot of residuals is derived from the conventional calibration curve and expressed in terms of the percent error in molecular weight. The deviation of the calibration data from the fitted line was approximately 10% for the conventional molecular weight and intrinsic viscosity calibration curves. It became 20% for the universal calibration curve. LALLS and DV detectors were used together with the DRI detector to provide evidence that the calibration curve deviations were due to the column packings and not due to some other cause (e.g., vendor values of molecular weight). Use of a polynomial fit to a portion of the curve corresponding to the retention volume range of an unknown was used to show the significant improvement in results which occurred when the calibration variations were taken into account. At present, use of many individual narrow standards is necessary to elucidate the effect.