Studies on the states of water in separation media of aqueous liquid chromatography in relation to separation selectivity

Abstract

The states of water incorporated in a cross-linked dextran (Sephadex G-10, G-15), polyacrylamide (Bio-Gel P-2, P-4), a polyethylene glycol (TSKgel Ether-250), cross-linked poly(vinyl alcohol) (Toyopearl HW-40S, 50S, 55S, and 75S), and polystyrene-divinylbenzene copolymer gel packings (TSKgel Styrene-60 and Styrene-250) were investigated by means of differential scanning calorimetry. It was found that there were three types of water in these gels; non-freezing water, intermediate or freezable bound water and free or bulk water. The amount of water that functions as the stationary phase in the column packed with the each gel was also estimated by a liquid chromatographic method. The estimated amount of the stationary phase water is in good agreement with the sum of the amount of non-freezing water and that of intermediate water for Sephadex G-10, G-15, Bio-Gel P-2, P-4, and Toyopearl HW-40S, 50S, 55S, while it agrees with the amount of only non-freezing water for TSKgel Ether-250 and Toyopearl HW-75S. This means that the stationary phase water consists of non-freezing water and freezable bound water for the former hydrophilic polymer gels, while only non-freezing water functions as the stationary phase in the latter two gels. On the other hand, no water in the polystyrene-divinylbenzene copolymer gels functioned as the stationary phase. This result can be attributed to the differences in the affinity of the polymer matrix for water molecules and in the structure of the gels; the hydrophilic polymer gels containing a polymer matrix at relatively high concentrations have a homogeneous gel phase, whereas the others have a heterogeneous gel phase consisting of hydrated polymer domains and macropores with a relatively hydrophobic surface. The freezable bound water in Toyopearl HW-75S and TSKgel Ether-250 as well as that in TSKgel Styrene-250 may be water isolated in pores of the hydrophobic domains. © 2006 The Japan Society for Analytical Chemistry.