Semi-microcolumn high-performance liquid chromatography

Attempts to miniaturize columns for liquid chromatography (LC) have been reported since the late 70's. A series of advantages were repeatedly claimed in the use of microcolumns, whose inner diameters were less than 1 mm. However, several requirements and limitations have kept microcolumn LC within a very limited area of applications. On the contrary, semi-microcolumn LC (inner diameter: 1 similar to 2 mm) has been widely accepted in academia and industry, possessing both advantages shown by microcolumn LC and the reliability of conventional LC. Although certain modifications, such as miniaturizing dead volumes of components, are required in instrumental arrangements, it became possible to easily obtain highly efficient separation with a semi-microcolumn, even under isocratic conditions. The benefits of semi-microcolumn LC seem most pronouncing when a column-switching system is arranged. A tremendous concentrating effect could be earned by first injecting a sample solution into a short conventional-bore precolumn, and then transferring an analyte-containing fraction to a semi-microcolumn connected into a detector. This analytical format was applied to the analysis of various substances contained in biological liquids at very low concentrations. The later sections of the article discuss some of these applications, including forensic analysis and diagnosis in clinical chemistry.