Some reflections on speed and efficiency of modern chromatographic methods

The development of high-performance liquid chromatography in the years 1965-1985 was undeniably a success story. Nevertheless, during those years a painstaking limitation of the technique, noticed by some and ignored by other workers in the field, remained: the resolving power accessible in a reasonable analysis time is poor, at least in comparison to capillary gas chromatography. The latter technique went through a delayed, but comparable success story during the same years. The limitation is well described in terms of the Knox concept of separation impedance; the available pressure limitation determines that the analysis time increases in proportion to the square of the plate number, i.e., to the fourth power of the resolution aimed at. By the introduction of a range of miniaturized liquid phase fractionation techniques, exploiting either classical pressure or electrical propulsion, a new era appears to have begun. Since then efficiencies similar to those in gas chromatography are accessible. The price to pay is the miniaturization needed. This leads to an aggravation of the detection problems. In this contribution an attempt is made to compare various techniques in terms of attainable efficiency and speed as well as of the demands on the detectors. Some speculations on future proliferation will be given. (C) 1997 Elsevier Science B.V.