Gas chromatography

Gas chromatography (GC) provides separation and quantitative analyses for volatile, thermally stable compounds in a broad variety of mixtures, from the simplest to the most complex ones. Packed columns range in sizes from capillary dimensions to preparative columns having inner dimensions of centimeter proportions. There are a number of aspects differentiating packed and capillary GC columns. While the back pressure in packed columns prohibits lengths in excess of 5–10 m, the ease of carrier flow in capillary columns allows much longer columns to be used. Their similar plate heights confer significantly greater efficiency to the capillary column. Thus, components with similar separation factors are better resolved in the capillary column, whereas packed columns must rely on phase selectivity to provide resolution in some instances. The chapter also describes an alternative mode of analysis—multidimensional gas chromatography (MDGC)—where two columns are employed, but only designated fractions are allowed to pass through the second column.