During the last years, there has been a marked increase of interest in column liquid chromatography (LC). One reason that this technique, whose discovery preceded gas chromatography (GC) by many years, has not been used extensively until relatively recently, has been due to the inherent shortcoming of suitable detection devices to times involved. Promising improvements in detector design during the last years, however, have made it possible to use a number of different modes of detection with highspeed, highefficicncy liquid chromatographic columns.
High resolution column LC is a technique which is experimentally analogous to GC, in that one makes use of small sample sizes (microlitrc quantities), long, narrow bore columns, fast moving liquids, and continuous and highly sensitive detection dcviccs. The term "liquid chromatography" includes several distinct types of interaction, i. å., (1) liquid-liquid, in which the components arc separated by partitioning between a mobile and stationary liquid; (2) liquid-solid, in which the components arc selectively adsorbed on an active surfacc; (3) ion exchange, in which ionic components of the sample arc separated by selective exchange with replaceable ions of the support; (4) permeation, in which separations occur on a permeable gel by a sieving action based on molecular size.
The advantage of liquid chromatography is that thermally unstable, nonvolatile compounds which cannot be cluted by GC, can often be separated by LC, since columns are operated at or near room temperature. Applications therefore seem feasible for such high molccular weight compounds as proteins and polymers. Too, the interchange of solvents can provide special selectivity cffccts in LC, since the relative retention of two solutes is strongly influenced by the nature of the elucnt used. Although LC is not likely to replace GC as an analytical technique, the two methods should complement one another.
The current interest in column LC is evidenced by numerous articles which arc now appearing in the literature. Column liquid chromatography has been successfully employed by several workers in the analysis of steroids, herbicides, insecticides, metal organic compounds and biologically active materials. Recently, reports have appeared, describing improvement in performance and efficiency of LC columns by the development of controlled surfacc porosity supports and by the use of high speeds and high pressures, enabling the technique to become competitive with GC.