Packed columns classification

LeseUier E, West C. Description and comparison of chromatographic tests and che-mometric methods for packed column classification. J Chromatogr A 2007 1158 320-60. 

Each of the PLgel individual pore sizes is produced hy suspension polymerization, which yields a fairly diverse range of particle sizes. For optimum performance in a chromatographic column the particle size distribution of the beads should be narrow this is achieved by air classification after the cross-linked beads have been washed and dried thoroughly. Similarly, for consistent column performance, the particle size distribution is critical and is another quality control aspect where both the median particle size and the width of the distribution are specified. The efficiency of the packed column is extremely sensitive to the median particle size, as predicted by the van Deemter equation (4), whereas the width of the particle size distribution can affect column operating pressure and packed bed stability. 

Packed Columns. If the stationary phase is a liquid, it is held in the column on an inert solid support, which will still appear dry. This support, or an active solid, is the material packed in the column. The nature of these packed beds was discussed in Chapter 2. Theory predicts that improved performance should result from the use of small particles, so some attempts have been made to pack them into columns. Because the diameter of these columns is usually small too, they have been called packed capillaries or, more generally, micropacked columns. Packed columns with a dpldc 0.3 have been put in this classification and reviewed.5 Some very high efficiencies have been obtained, but sometimes at the expense of very high inlet pressures. 

The system constants for packed column stationary phases are summarized in Table 8. Classification of their properties by cluster analysis results in the connection dendrogram shown in Figure 4. Stationary phases with similar solvation properties are located next to each other and connected close to the left-hand side of the dendrogram. Stationary phases with no paired descendents are singular phases with properties that cannot be duplicated by other phases from the data set (Table 8). Classification results in six groups with three phases behaving... 

This chapter discusses the types of stationary phases, their classification, their applications, and the criteria used in selecting an appropriate liquid phase for a given separation. With packed columns, the choice of the stationary phase is critical, but it is less so for open tubular columns because of their higher efficiency. Individual chapters are devoted to each of the two column types, and this chapter is more relevant for packed columns (Chapter 5). 

Two types of gas chromatography exist gas-liquid chromatography (GLC) and gas-solid chromatography (GSC). Other classification schemes such as GSC. GLC plus capillary gas chromatography (CGC) are outdated because nowadays GLC and GSC can be performed both in packed columns and in capillary or open tubular columns,... 

There were several significant consequences resulting from these classification procedures. Phases that have identical chromatographic behavior also have identical constants. In this case the selection of a stationary phase could be based on a consideration such as thermal stability, lower viscosity, cost, or availability. McReynolds constants of the more popular stationary phases for packed column GC are listed in Table 3.8. Note that the DC-200 (a silicone oil of low viscosity) and OV-101 or SE-30 (a dimethylpolysiloxane) have nearly identical... 

D. Kite, Jr, Safety Hazard Classification of Water-Wet Explosives , PATR 3223 (1965) (AD-460363/5ST) [Table 7 lists deton data for 18 granular w-filled expls loosely packed in Plexiglas tubes of 1.75" ID with wall thicknesses of from 1/8" to 1/4". Expl column lengths were from 10" to 20". Deton was achieved using either 33g Tetryl pellets or 40-grain RDX wafers, electric cap initiated. 

Specific and essentially stand-alone mode of liquid chromatography is associated with the absence or suppression of any analyte interactions with the stationary phase, which is called size-exclusion chromatography (SEC). In SEC the eluent is selected in such a manner that it will suppress any possible analyte interactions with the surface, and the separation of the analyte molecules in this mode is primarily based on their physical dimensions (size). The larger the analyte molecules, the lower the possibility for them to penetrate into the porous space of the column packing material, and consequently the faster they will move through the column. The schematic of this classification is shown in Figure 1-1. 

Special processes have been developed to manufacture spherical packing materials with a given particle size distribution. The size distribution is narrowed by a size classification process, e.g. by air elutriation. Typically, the average particle size of a packing for an analytical column lies between 3 and 5 xm, the dp of a packing for preparative columns ranges from 10 to 50 xm. 

There are two general classifications of gas chromatographic columns, packed and capillary or open tubular columns. 

These are arbitrary classifications of chromatographic techniques, and some types of chromatography are considered together as a separate technique, such as gas chromatography for gas-solid and gas-liquid chromatography. In every case, successive equilibria are at work that determine to what extent the analyte stays behind or moves along with the eluent (mobile phase). In column chromatography, the column may be packed with small particles that act as the stationary phase... 

The flame ionization detectors (as well as the other flame detectors) can be used equally well with packed and capillary columns. Different considerations may apply to other detector types. The well-known classification of chromatographic detectors into the concentration-sensitive and the mass-flow-sensitive types is highly relevant in this respect. A response enhancement [108] to the mass-flow-sensitive detector types is given as... 

A range of particle sizes can be produced from the reaction just described. For packing materials to be as homogeneous as possible, with uniform flow channels, particles of equal size are most suitable. Narrow particle size distributions and regular, spherical particles are therefore desirable (8). If the particle size distribution is too broad, the permeability of the column decreases. Refinement of particle size distribution by some form of particle classification is used to produce narrow distributions for optimum performance. 

The classification of polymer mesophases have been considered in many reports (P-70). On analyzing the published data there arises much controversy in the identification. In order to avoid confusion in terminology it is necessary to define the basic terms relating to polymer columnar mesophases before further discussion. Columnar polymer systems have both a correlation of the centers of gravity and molecular orientation, but have mesomorphic properties due to the conformational disorder both of the polymer back-bone and side chains. The structural unit of the polymeric columnar mesophase is a macromolecule. In columnar phases macromolecules form regular 2D-periodic arrays. The two-dimensional symmetry of the column packing and the parameters of two-dimensional lattice are strongly dependent on the form and dimensions of the cross-section of a polymer molecule. 

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