GC Columns

The most common form of GC columns used in the fragrance industry is the wall-coated, open tubular (WCOT) type. These are made of fused silica tubing coated with a thin film of stationary phase on the inside and covered with polyamide on the outside for protection. Fused silica columns are usually between 25 m and 60 m long, with inner diameters from 0.53 mm to 0.1 mm. A widely used range of stationary phases is based on phenyl-substituted methyl silicones. The polarity of the phase is determined by the number of phenyl groups, a greater proportion of which increases the polarity of the phase. OV-1 is a common ‘non­polar’ stationary phase composed of dimethyl siloxane, while SE-54 is a more polar phase in which 5% of the dimethyl groups have been substituted with phenyl groups (Figure 12.2). Phases with greater polarity are achieved by using polyethylene glycol (PEG). The range of GC stationary phases is being modified continuously and expanded

OV-1 type





Figure 12.2 Common GC stationary phases

with new materials for specific applications. Cyclodextrin-based sta­tionary phases are now available commercially for the separation of optical isomers, a technique referred to as Chiral-GC.

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