Principles and Practice of Chromatography - Molecular Forces and Chromatographic Selectivity > Separations Based on Polar Interactions > Page 32

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Figure 13 The Separation of Some Airborne Contaminants by GC


The solutes that disclose the nature of the interactions that are taking place with the two stationary phase are methanol and benzene. On the polyethylene glycol stationary phase, methanol (B. Pt. 64.7oC, polar) and benzene (B. Pt. 80.1oC, polarizable) are eluted well after n-heptane (B. Pt. 98.4oC, dispersive) and 1-heptene (B. Pt. 93.6oC, dispersive and slightly polarizable). The strong polar interactions between the OH groups of the polyethylene glycol and both the OH groups of the methanol and the polarized nucleus of the benzene are far greater than the dispersive interactions with heptane and heptene. This difference occurs despite the greater molecular weights and higher boiling points of heptane and heptene. On the stationary phase Carbopack, methanol, weakly dispersive, is eluted almost at the dead volume while the more dispersive solutes are extensively retained.