Polarity in chromatography is not normally expressed in terms of the dielectric constant but empirically, for chromatographic separations, the rule of thumb is that 'like separates like'. This means that for gas chromatographic analysis, non-polar analytes are best separated by non-polar stationary phases. A hydrocarbon stationary phase such as squalene (a terpene hydrocarbon)for instance, will separate a mixture of hydrocarbons such as butane, pentane, heptane and nonane. Thus it is necessary for chromatography laboratories to have a range of columns available, in order to be able to select the most appropriate column to perform a particular analysis. Note: In tlc (see Chapter 6 of this teaching and learning programme), it was the polarity of the mobile phase which was 'matched' to that of the analytes.
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