Chromatography is a separation analysis method, separation is the core, so the separation of the chromatographic system is the heart of the chromatography system. The column requirements are column efficiency, selectivity, analysis speed and so on. Commercially available microparticulate fillers for HPLC such as porous silica and silica gel-based bonded phases, alumina, organic polymeric microspheres (including ion exchange resins), porous carbon and the like, typically have a particle size of 3,5 , 7,10μm, etc., the theoretical efficiency of up to 5 ~ 160,000 / m. For general analysis only 5000 plates efficiency; for homologue analysis as long as 500 can be; for more difficult to separate the material can be used up to 20,000 columns, so the general length of about 10 ~ 30cm can Meet the needs of complex mixture analysis.
Column efficiency is affected by internal and external factors. To achieve the best efficiency of the column, the column should have a reasonable column structure (minimize the dead volume outside the packed bed) and the filling technique in addition to the small dead volume outside the column. Even the best filling technology, the filling of the central part of the column and along the tube wall is always not the same. The parts close to the wall of the tube are loose and easy to produce ditches. The flow velocity is faster and the flow of the rinsing agent is affected. Band widening, which is the wall effect. This tube wall area is approximately 30 times the thickness of the tube wall inward. In a typical LC system, the effect of extra-column effects on column efficiency is much greater than the tube wall effect.
Column by the column, pressure cap, card sets (seal ring), sieve (filter), connectors, screws and other components. Column tube made of stainless steel, the pressure is not higher than 70 kg / cm2, but also thick-walled glass or quartz tube, the tube wall requires a high finish. In order to improve the efficiency, reduce the wall effect, the stainless steel column wall after polishing. Some people in the stainless steel column coated with fluorine plastic inner wall to improve the finish, the effect and polishing the same. There are also fused silica or glass liners for thin columns. The columns at both ends of the column are equipped with a sieve plate, sintered stainless steel or titanium alloy, pore size 0.2 ~ 20μm (5 ~ 10micro m), depending on the particle size, the purpose is to prevent the filler leakage.
Column by analysis can be divided into two types of preparation and preparation, size specifications are also different: conventional analytical column (constant column), diameter 2 ~ 5mm (commonly used 4.6mm, the domestic 4mm and 5mm), column length 10 ~ 30cm ; narrow bore (narrow bore, also known as semi-microcolumn semi-microcolumn), diameter 1 ~ 2mm, length 10 ~ 20cm; capillary column (also known as microcolumn microcolumn), an inner diameter of 0.2 ~ 0.5 mm; semi-preparative column, an inner diameter of> 5mm; laboratory preparation column, an inner diameter of 20 ~ 40mm, column length 10 ~ 30cm; Column diameter is generally based on column length, particle size and the equivalent flow rate to determine, the purpose is to avoid the tube wall effect.
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