Temperature effect on HPLC retention of PCBs on porous graphitic carbon

The effect of column temperature on solute retention was investigated for 10 PCBs with different degrees of planarity (degree of ortho position substitution). The variation of retention values (ln k) with temperature was measured using two solvents, n-hexane and dichloromethane, as mobile phase: retention decreases as temperature increases. The relationship between ln k values and temperature (1/T) exhibits a good linearity. The ΔH0 values calculated are in the -2 to -5 kcal mole-1 range: they are very similar for compounds with the same degree of ortho-substitution and are significantly higher for non-ortho substituted congeners. High temperature significantly improves separation efficiency (plate number significantly increases): this effect is the dominant factor controlling chromatographic resolution, which improves with increasing temperature. Operating at 40 °C, an efficient separation of planar PCBs was obtained with low solvent consumption.