Gas chromatography 'polarity' of thin, bonded layers (modified supports)

Modified gas chromatographic supports based on very thin, non-extractable layers of Carbowax 20M on Chromosorv W have become popular phases, and other polymer—support combinations may follow. It is therefore desirable for the practitioner of gas chromatography to know something about the “polarity” of these phases. The available polarity scales predicated on gas—liquid partition involving heavy loads of liquid phase. Thus they are not, in principle, applicable to very thin, bonded layers. In practice, however, it is helpful to know that supports modified by pola materials such as Carbowax 20M or polyethylene glycol adipate appear much less polar than their regular gas—liquid chromatographic counterparts, i.e., packings with heavy loads of Carbowax 20M or polyethylene glycol adipate: the retention indices for typical probes differ by ca. 100–400. Phases based on non polar materials, e.g., Apiezon L, can show the opposite effect.