Abstract
Two silica gels, untreated and thermally pretreated at 1000°C, were coated with different loadings (6, 15, 25 wt%) of Carbowax 20M. The surface of the coated silica gels was characterized by means of nitrogen adsorption measurements at - 196°C and infrared spectroscopy. It was found that the coating reduces the surface dimensions of silica gel due to free entrance of polymer molecules occupying preferentially the micropores in the 5-60 Å range. Infrared spectroscopy indicated that the low polymer loading (6 wt%) is not sufficient to deactivate the surface of silica gels. Surface deactivation of unmodified and coated silica gels was also confirmed via thermodynamic parameters (ΔH and ΔS) which were calculated by the aid of inverse gas chromatography using n-hexane as a probe. The coated silica gels were evaluated as gas chromatographic stationary phases using two groups of nonpolar and polar solutes. The efficiency of chromatographic separation was discussed in terms of surface deactivation and pore structural changes brought about by different polymer loadings.