Liquid Chromatography - Introduction 2
The statement made by Martin in 1941 contains all the necessary conditions to realize both the high efficiencies and the high resolution achieved by modern LC columns. Despite his recommendations, however, it has taken nearly fifty years to bring his concepts to fruition. Activity in the field of liquid chromatography was eclipsed in the 1950s by the introduction of gas chromatography and serious attempts were not made to improve LC techniques until the development of GC neared completion in the mid 1960s. The major impediment to the development of LC was the lack of a high sensitive detector and it was not until the refractive index detector was developed by A. Tiselius and D. Claesson (4) in 1942 could the technique be effectively developed.
Tswett's original LC consisted of a vertical glass tube, a few centimeters in diameter and about 30 cm high, packed with the adsorbent (calcium carbonate). The plant extract pigments was placed on the top of the packing and the mobile phase carefully added to fill the tube. The solvent percolated through the packing under gravity, developing the separation which could be seen as different colored bands at the wall of the tube. The simple apparatus of Tswett contained all the essentials to achieve a chromatographic separation.
The contemporary chromatograph, however, is a very complex instrument operating at pressures up to 10,000 p.s.i providing flow rates ranging from a few microliters per minute to 10 or 20 ml/minute depending on the type of LC that is carried out. Modern detectors can detect solutes at concentration levels of 1x10-9 g/ml and an analysis can be completed in a few minutes with just a few micrograms of sample.