Polydextran column

Figure 13.4. Apparent MWs of HS from different environments as determined by SEC [compiled from the data reported by Perminova et al. (2003)]. Bars represent a range of weight-averaged molecular weights determined for different groups of humic materials. Two black dots represent two IHSS standards Suwannee River FA and HA. SEC chromatograms were obtained with column-packing Toyopearl HW-50S using 0.028 M phosphate buffer at pH 6.8 as a mobile phase. Two different sets of standards were used to calibrate the column polystyrene sulfonates (PSS) and polydextrans the upper MW scale corresponds to dextran calibration and the bottom one—to PSS calibration.

There are two classes of stationary phases in SEC, one type for GFC and the other for GPC. Stationary phases for GFC are hydrophilic and include polydextrans, polyvinyl alcohol gel, and silica gel those for GPC are hydrophobic, typically cross-linked, rigid polystyrene-divinylbenzene gels. Generally, columns of 15 to 50 cm length are used, packed with 7- to 10-/t,m particles and with an internal diameter between 0.6 and 0.8 cm. In SEC, unlike in other chromatographic modes, the stationary phase is the primary factor controlling retention. 

In addition to the classical column packing materials (silica gel, alumina, celite), other widely used columns are of the polydextran gel type for the fractionation of the polar steroids, Sephadex LH-20, and for the less polar steroid compounds its hydro-xyalkyl derivative, Lipidex. The use of ion exchange columns (e.g., DEAE-Sephadex A-25, Amberlite XAD-2) is also widespread. High selectivity is attainable with immunoaffinity chromatography, where antibodies are immobilized on chemically modified agarose gel and filled in columns. For the solid-phase... 

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