Strategies for speed optimisation in gas chromatography: an overview

An overview is given of existing methods to minimise the analysis time in gas chromatography being the subject of many publications in the scientific literature. Packed and (multi-) capillary columns are compared with respect to their deployment in fast gas chromatography (GC). It is assumed that the contribution of the stationary phase to peak broadening can be neglected (low liquid phase loading and thin film columns, respectively). The treatment is based on the minimisation of the analysis time required on both column types for the resolution of a critical pair of solutes (resolution normalised conditions). Theoretical relationships are given, describing analysis time and the related pressure drop. The equations are expressed in reduced parameters, making a comparison of column types considerably simpler than with the conventional equations. Reduction of the characteristic diameter, being the inside column diameter for open tubular columns and the particle size for packed columns, is the best approach to increase the separation speed in gas chromatography. Extremely fast analysis is only possible when the required number of plates to separate a critical pair of solutes is relatively low. Reducing the analysis time by reduction of the characteristic diameter is accompanied by a proportionally higher required inlet pressure. Due to the high resistance of flow of packed columns this seriously limits the use of packed columns for fast GC. For fast GC hydrogen has to be used as carrier gas and in some situations vacuum-outlet operation of capillary columns allows a further minimisation of the analysis time. For fast GC the columns should be operated near the conditions for minimum plate height. Linear temperature-programmed fast GC requires high column temperature programming rates. Reduction of the characteristic diameter affects the sample capacity of the ‘fast columns'. This effect is very pronounced for narrow-bore columns and in principle non-existing in packed columns. Multi-capillary columns (a parallel configuration of some 900 narrow-bore capillaries) take an intermediate position