Determination Of Pore Size Distribution Of Porous Media By Inverse Size-exclusion Chromatography

Chromatography is an effective method to separate biomacromolecule. The separation performances are directly influenced by the pore structure of porous adsorbents, with the pore size distribution (PSD) playing a major role. Inverse size-exclusion chromatography (ISEC) has been used for determining the PSD of porous media, which are more suitable for soft materials than traditional methods, such as gas sorption and mercury intrusion. The fundamentals and applications of ISEC in the characterization of the pore structure are reviewed, and this method is developed and used to determine the PSD of a series of chromatographic adsorbents.Firstly, the mathematical models used in ISEC are discussed. The most used PSD models are Gaussian distribution and log normal distribution, and the most used local partition coefficient model is spherical solutes in cylindrical pores model. These models are also used in the present work. As a result, using log normal distribution can avoid the minus value of radius which may appear with Gaussian distribution in some cases. Compared to sp, more accurate rp can be obntained. because it was found that rp play an important role in Kd but sp don't.Secondly, the experimental method of ISEC to determine the PSD of chromatographic adsorbents is developed, and the feasibility and reliability of the method is verified. The model calculation fitted well with the experimental data. The results demonstrate that ISEC is a feasible method to determine the PSD of porous chromatographic media. In addition, some parameters can be calculated from the PSD, such as the accessible internal pore surface area.Thirdly, ISEC is used to determine the PSD of series of agarose-based chromatographic adsorbents. The impacts of agarose concentration during the gel preparation are investigated, and it was found that the pore radius is larger as the agarose concentration is lower. Then FF series of ion-exchange resins (based on 6% agarose gels) with different functional ligands of Q, SP, DEAE and CM are studied. The PSDs of these ion-exchange resins are quite similar, and as same as that of 6% agarose gel base. In addition, different gel types of ion-exchange resins are investigated, including FF, XL and HP series. The pore radius of XL series is much smaller than that of FF series. The pore radius of HP series is a little larger than that of FF series and the size distribution is much wider.Finally, the PSD of some polysaccharide media, organic synthesis media, as well as home-made cellulose media developed in our laboratory are determined. As a result, the PSD of FF ion-exchange resins (based on 6% agarose gels) that are produced by different companies are a little different, but not far away, and the pore size of this type of media are larger than that of cellulose media tested. The PSD of organic synthesis media is larger and wider than that of polysaccharide media. In addition, the PSD of six home-made cellulose media are very narrow, and the pore-enlarged agents are effective.