Optimization of Column Design and Operating Parameters In High Speed Liquid Chromatography

Abstract

Using the fundamental equations for the resolution and the carrier liquid flow velocity and assuming that the HETP is proportional to dpβ uγ the authors derive a general equation relating the analysis time to the column design and operating parameters, to the characteristics of the chromatographic system selected and to the resolution desired. The discussion of this equation allows the optimization of these parameters and shows the cost of resolution. The interest in the use of particles of small diameters to pack the columns and of large inlet pressures is explained and quantitatively accounted for. As expected, the use of small particles induces a very steep increase of the inlet pressure necessary to ensure the high velocities at which analyses are presently carried out. The pressure requirements, however, can be drastically reduced by using shorter columns and by working at lower velocities, provided that the velocity remains larger than the one corresponding to the minimum plate height. Whenever this condition is fulfilled, excellent chromatographic performances can be achieved with pressures not exceeding a few tens of bars. However, the use of very efficient, short columns presently available requires very stringent detector specifications. Finally, for various independent reasons, it seems that in practice the lower limit in the average diameter of packing particle lies somewhere between 2 and 5 µm at the present time.