A mathematical model for hydrodynamic and size exclusion chromatography of polymers on porous particles

The fractal calibration method applied to the characterization of polymers in solvent mixtures and in mixed gel packings by SEC

The size-exclusion chromatographic (SEC) behaviour of different solvent/polymer systems in three packing sets has been analysed from fractal considerations. The three-column sets studied are specifically formed by: (i) 'pure' micro-styragel, (ii) 'mixed' TSK Gel H(HR + XL + HR) and (iii) mixed TSK Gel H(XL + HR + XL). The experimental data reveals that in most of the systems assayed the classical universal calibration (UC) is not fulfilled, denoting the existence of secondary effects accompanying the main SEC mechanism. In order to obtain an accurate characterization of different polymers eluted in solvent mixtures and/or mixed packings, the use of a reliable and trusted calibration curve is required. In this sense, two alternative procedures have been analysed: the specific (SC) and the fractal (FC) calibrations. The results have evidenced that the use of the FC instead of the classical universal method diminishes up to nine times (in the case of the micro-styragel set) the mean deviation on the calculated molar mass with respect to the value given by the supplier. In the case of TSK Gel-based sets, the mean deviation is reduced to the half. The SC curve made with standards of the sample under study also reduces the mean deviation values but needs a broad set of narrow standards, whereas the fractal approach only needs one polymeric sample to build up the calibration curve.

Distribution analysis of ultra-high molecular mass poly(ethylene oxide) containing silica particles by size-exclusion chromatography with dual light-scattering and refractometric detection

Two different size-exclusion chromatography (SEC) systems, connected in-line either to a low-angle light scattering (LALS) or to a multiangle light scattering (MALS) detector, are employed for determination of molecular mass distributions (MMD) of poly(ethylene oxide) (PEO) samples having a weight average molecular mass up to eight millions. The detrimental effect of the presence of strongly scattering silica particles in the samples on the light scattering signal can be eliminated using a suitable sample dissolution procedure utilizing silica solubility in aqueous mobile phase. The selection of flow-rate and sample concentration have a large impact on the obtained results. Hydrodynamic retardation phenomena and nonlinearity effects are shown to introduce severe errors in the molecular mass distributions unless flow-rate and sample concentration are kept at sufficiently low levels. Self-compensating ability of the dual detection in flow-rate effects is shown to be the main advantage here. A good agreement between the results obtained using LALS and MALS detection is found provided that a carefully selected angular extrapolation procedure is used in the case of MALS data. Thus, using carefully selected experimental conditions, SEC with light-scattering (LS) and refractometric detection proved to be an efficient technique for MMD characterisation also of ultra-high molecular mass (UHM) PEO polymers.

Fractal calibration in size-exclusion chromatography I. An introduction

The elution behaviour of different polymer-solvent systems in three types of organic columns for SEC has been compared and interpreted. The experimental data show that the classical universal calibration is not accomplished. Deviations from a unique curve are observed due to the binary and ternary interactions between the components of the system (solvent, polymer and gel) which results on secondary mechanisms accompanying the main pure or "ideal" SEC separation mechanism. Both, enthalpic and entropic effects are interpreted in terms of the swelling and crosslinking degrees of the gel packings, and are also related with the fractal characteristics of their surfaces, such as the fractal dimension and the available pore size. Moreover, a relationship between the fractal dimension of the pore surface and the chromatographic distribution coefficient is proposed.

Separation in slalom chromatography: stretching and velocity dependence

Slalom chromatography (SC) is used for the separation of large double-stranded DNA molecules. In this technique, the progression of the DNA fragments through the closed column packing follows the flow direction and is like a snake edging is way into long grass. A novel mathematical model is developed in this paper to describe this hydrodynamic phenomenon. The results obtained provided a model for the resolution between two adjacent peaks on a chromatogram. As well, a chromatographic response function was used to obtain the most efficient separation conditions for a mixture of DNA fragments with sizes higher than 15 kbp in a minimum analysis time.

Supercoiled circular DNA and protein retention in non-equilibrium chromatography temperature and velocity dependence: testimony of a transition

Non-equilibrium chromatography (NEC) is a chromatographic mode for the rapid separation of polymers. The retention behavior of various proteins (human, chicken, bovine serum albumin) and supercoiled circular double-stranded DNA (plasmids) was investigated using a phosphate buffer as a mobile phase at different velocities and column temperatures with a C1 column with very low-packing particle diameter as a stationary phase. It was shown that the two factors (temperature and velocity) constituted important parameters in the retention mechanism of plasmids and proteins in NEC. The protein was retained more than the plasmid. At all the temperatures (5, 10, 15, 20, 25 degrees C) the plasmid retention increased over the entire flow-rate range (0.02-1.8 ml/min). For the protein, the retention curve presented a decrease in the relative retention time until a critical value of the mobile phase flow-rate, followed by an increase. The transition between the two well known NEC methods, slalom chromatography and hydrodynamic chromatography was clearly visualized for proteins at the lowest temperature, but did not appear for plasmids due to their strong compact structure.