Columns mechanical packing

Although hplc columns are packed under high pressure, the column bed can be disturbed by sudden pressure variations, or mechanical... 

Enantiomeric separation is a great challenge. Every separation requires a dedicated column. Some packings are more able to separate many racemates. When a chiral selector is used as the stationary phase, the primary retention mechanism is complexation with the surface-... 

Hindered diffusion, the primary transport mechanism in porous solids, can be qualitatively described as a series of hops by the analyte, via gas-phase diffusion, from one surface site to the next. Thus, hindered diffusion is composed of two main components a pure diffusion-related term, often Fickian in nature, associated with movement of the analyte in the gas phase and a term describing the noninstantaneous equilibration between gas-phase analyte and the solid surface at each point where the analyte touches down (adsorbs). In extended porous solids (e.g., a chromatographic column tightly packed with porous beads), transport is often more complex, requiring the consideration of such factors as eddy diffusion and Knudsen effusion. This is important if there is a significant pressure drop along the path of the analyte [109]. Finally, the presence of any external fields (thermal, electric, etc.) must be considered as well. 

Mechanical reciprocation Karr Column Pulsed Packed Column Pulsed Perforated Plate Column... 

Gas chromatography is a separation technique based on the fact that different components in the mixture exhibit different average residence times due to interactions with the porons packing material. These interactions can be classified as intrapellet diffusion and the column operates similar to a packed catalytic tubular reactor. The important mass transfer mechanisms are convection and diffusion. Hence, it is important to calculate the mass transfer Peclet number that represents an order-of-magnitude ratio of these two mass transfer rate processes. Intrapellet diffusion governs residence times, and interpellet axial dispersion affects the degree to which the output curve is broadened. For axial dispersion in packed columns and packed catalytic tubular reactors. 

Values of the mass transfer coefficients and interfacial areas for the more common contactors (packed columns, plate columns, bubble columns, mechanically agitated contactors, and static mixers) are usually known, or can be estimated from correlations published in the literature, or are supplied by the manufacturers. Typical values are given in Table 16.1. 

N 0.03 0.03-CJVcolumn Packed column Plate column Mechanically agitated contactor... 

These two packing techniques can be used for column diameters up to about 10 cm columns having diameters greater that 10 cm usually employ particles with diameters greater than 20 pm and thus, can be dry packed. The two mechanical packing methods are depicted in figure 9.6. 

Moreover, it should also be noted that an increase in pore size also leads to reduced mechanical stability, since the structure of the support becomes thinner. This is particularly important with materials for UffPLC because there the pressure can reach 1500 bar and the columns are packed at even higher pressures. 

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