Microparticulate high efficiency columns

McCalley, D.V. (2002). Comparison of conventional microparticulate and a monolithic reversed-phase column for high-efficiency fast liquid chromatography of basic compounds. J. Chromatogr. A 965, 51-64. 

Analytical hplc these days is nearly always done with microparticulate column packings, which are small porous particles, usually spherical or irregular silica, with nominal diameters of 3,5 or 10 fxm. They combine the best features of the other two types, having high efficiency as well as a large surface area. In bulk, the appearance of a microparticulate silica resembles that of a fine talcum powder. With microparticulates, dry packing methods result in column beds that are unstable under pressure, so they are packed into columns using a slurry of the material in a suitable solvent and under considerable pressure. 

Currently, almost all the available SEC columns are packed with the high efficiency, microparticulate packings (<10u). Recent state-of-the-art developments on column packings have been described by Majors (10). A listing of such type of packing materials is shown in Table 1. 

One can see three routes to an increase in the value of resolution First, one can increase the plate number N which results in an increase in resolution proportional to the square root of N The use of microparticulate packings was a major breakthrough in this respect If we assume, however, that the chromatographer already has at his disposal a high efficiency column, then he must go to great... 

Since efficiencies for microparticulate columns are very high (optimum H values of 0.01-0.03 mm), only short columns (15-25 cm) are required for analytical HPLC, as can be seen in Figure 21.14C. The use of 5- m particles implies greatly increased column back-pressures compared to those produced by the larger porous or pellicular particles, as suggested by Equation 21.13. However, these short columns exhibit moderate back-pressures (less than 200 atm) when used at flow rates of... 

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