An Introduction to OPLC Operation and Applications

2 Introduction Column liquid chromatography (LC) systems are the mainstay in modern laboratory practice for both analysis and preparative isolation of natural and synthetic organic samples. Standard highand medium-pressure column LC uses an essentially one-dimensional (1D) format, (i.e., a cylindrical column onto which a single sample is injected). Optimum performance laminar chromatography (OPLC1), in contrast, is a pumpedflow chromatography system that uses a planar 2D column format. This can increase throughput by allowing side-by-side analysis of several samples in a single run, provide added loading capacity by using the whole column width for a single sample and improve separation efficiency by allowing twodimensional (2D) chromatography directly on a square column. The multidimensional capacity of OPLC is not limited to the separation technique alone, but also to the multitude of sample application and detection methods that are available.2 The acronym OPLC, also described as overpressured layer chromatography or forced-flow TLC, describes a technique that dates back to the late 1970s.42 The instruments at that time used nuts and bolts to compress a modified TLC plate between metal or glass sheets. There was little control over the pressure applied to the layer as this was a purely manual technique. The TLC plate was also modified by the user with the addition of a sealant to the edges of the plate. To distribute the solvent homogeneously across the layer, it was also necessary to scrape a horizontal line of silica from the plate directly below the solvent inlet. These aspects, and others not mentioned here, hindered the development of the technique in modern analytical laboratories. Three very important factors contribute to an optimized homogeneity of lateral and laminar flow inside the 200 μm thick sorbent bed. First, the introduction of electronic controls gives a better control of the chromatographic conditions and the quality of the separation.43 Second, factory-made flat columns have a high precision positioning and a more regular seal. Finally, the flowing eluent wall technology (FEW) dramatically reduces disturbances at the layer edge and the inlet site (see text below and Figure 1). The technology described in recent articles demonstrates the jump in progress that justifies a new terminology, optimum performance laminar chromatography introduced in 2000.44 This review will describe the basis of modern OPLC instrumentation and the separation techniques, as well as give a brief account of some recent applications in OPLC.