The Fractal Approach to Secondary Mechanisms in SEC

Abstract

Size-exclusion chromatography (SEC) is one of the most used experimental techniques to characterize polymers in solution; it has been applied to interpret the elution behaviour of many polymer-solvent systems in five types of column packings. The experimental data have revealed that the classical universal calibration is not accomplished. Deviations from a unique curve are a consequence of two effects: entropic (exclusion by size) and enthalpic (binary and ternary interactions between solvent, polymer, and gel), which results in secondary mechanisms accompanying the main "ideal" SEC separation mechanism. Therefore, three approaches of building a calibration curve have been compared in this work: (i) the classical universal calibration based on the elution of tetrahydrofuran (THF)-polystyrene (PS) system as reference; (ii) the specific or proper calibration curve made with standards of the sample under study; and (iii) the fractal calibration. The understanding of the secondary mechanisms has been based on the fractal characteristics of the porous gel surfaces, as well as on the swelling and crosslinking degrees. The global analysis of data has allowed us to propose an alternative relationship between the fractal dimension, D f , and the chromatographic distribution coefficient, K D , independently of the chemical nature of the solvent, polymer, and gel. From a quantitative point of view, the fractal methodology considerably reduces the deviations found when estimating polymer molar masses by SEC.

Treatment of poly(styrene‐co‐methacrylic acid)/poly(4‐vinylpyridine) blends in solution under liquid–liquid phase‐separation conditions. A new method for phase‐separation data attainment from viscosity measurements

“…After repose of 24 h two phases appear, which compositions are analyzed by liquid chromatography. Using CHCl 3 as eluent, RI as detector and the system equipped with three complete sets of TSK columns (with pore size names TSK Gel Super AW 2500, TSK Gel Super AW 3000 and TSK Gel Super AW 4000, suitable for any eluent,23 and able to completely separate PS with M n = 38,000 g mol −1 or PS‐MAA with M n = 33,000 g mol −1 from PVPy with M n = 25,000 g mol −1 , cf. Table II), copolymer and homopolymer have been calibrated separately (peak height versus quantity of injected polymer).…”

Size Exclusion Chromatography for the Quantitative Profiling of the Enzyme-Catalyzed Hydrolysis of Xylo-oligosaccharides

“…The elution of the polysaccharide is then determined by the time it takes for the polysaccharides to travel through the pores (10). To calculate the molecular weight of the polysaccharides, calibration curves can be constructed by measuring the retention volumes (or retention times) of synthetic polymer standards such as pullulan or polyethylene glycol molecules having a known narrow molar mass distribution (11).…”