Determination of Band Broadening in SEC from the Analysis of Narrow Standards with Molar Mass Sensitive Sensors

MEIRA, G.R.; VEGA, J.R.; YOSSEN, M.M.

Bratislava (Eslovaquia)

Congreso; 20th Bratislava International Conference on Macromolecules: Advanced Polymeric Materials (APM 2006); 2006

A theoretical method for estimating the (asymmetrical and non-uniform) band broadening function (BBF) in size exclusion chromatography (SEC) is extended to simultaneously estimate the BBF and the interdetector volume (IDV). The following data is required: a) the concentration- and molar mass chromatograms from a set of narrow standards; and b) the molar mass calibration logM(V). In the narrow range of each standard, the BBF is assumed uniform but skewed. Such uniform BBFs are estimated through a nonlinear optimization procedure that compares one of the measured chromatograms with its theoretical prediction based on the other. The BBF can be assumed arbitrary or represented by an exponentially-modified Gaussian (EMG). The EMG is defined by 2 parameters: the standard deviation and the exponential decay. The global non-uniform BBF covering the complete fractionation range is obtained by interpolation between the uniform BBFs. The extended method was validated with 2 SEC experiments involving different chromatographs, detectors, and column sets. In Exp A, the standards were analyzed with a MALLS detector (Wyatt Tech.) in series with a differential refractometer (DR). In Exp B, three PS standards were analyzed with a Viscotek 200 detector (containing a specific viscosity sensor SV in parallel with a DR). The precise determination of the IDV seems vital for an adequate estimation of the BBF, and this problem is particularly serious when the detectors are in parallel. The non-uniform BBFs resulted skewed, and somewhat narrower in the mid-range of elution volumes.