Plate number Polarity”

Plate number, 3,4,7, 27, 52, S3 Plates per second, 30-33 PLB, see Porous layer beads Polar group selectivity, 181-183 Polar solvent, selective uptake from eluent by polar adsorbent, 8S Polarizability, 206... 

Partition coefficient, 9, 10 Partition ratio, 11 time optimization of, 57-58 Peak, definition of, 69 Peak capacity, 18, 19 Pellicular supports, 157 Permeability, 63-64 Phase selection diagrams, 218-219 Phase volume ratio, 11 Pinkerton (ISRP) columns, 225-226 Plate height, 17 Plate number, 14-16 Plate theory, 3, 28 Polarity index, 210, 211 Pore size of LC supports, 157 Porosity, 27 Precision, 99-100 Preparative scale ... 

It is advisable to carry out practical measurements in order to determine the amount of solvent required, yield and plate number for the process. See the literature [4-6] for further details. The selectivity of the solvent is of special importance with solid-liquid extraction. If the solute to be extracted is chemically uniform, the required solvent can be selected based on the similar polarity with the solutes. Table 2.1 provides further details. 

The use of small spherical particles for NPC results in plate numbers in excess of 10,000 which compares favourably with the efficiencies of stationary phases currently in use for reversed phase HPLC. A list of the common functional groups used in NPC are shown in Table 6.1. Most of the popular supports used in NPC are silica based since alumina undergoes undesirable side reactions (e.g. irreversible reaction with carboxylic acid). The introduction of bonded phase supports has led to the availability of many other polar stationary phases, some of which can also be used in the reversed phase mode (Lochmuller et al., 1979). A bonded diamino phase was found to be optimal for aromatic hydrocarbons (Chmielowiec and George, 1980). 

During recent years, SFC methods for the characterization of lipids have been developed at the Arrhenius Laboratories. The separation of complex mixtures of TGs on non-polar open tubular SFC was first attempted. However, several TG species showed overlapping in the chromatograms, and it seems that at the present level of SFC performance it is not possible to perform such separations by virtue of plate number alone. Separation of TG species was also incomplete on more polar open tubular columns (van Oosten et al, 1991). Thus, separation has to be achieved by means of selectivity, and that is best performed on packed columns. Employing such columns, we have demonstrated the separation of neutral as well as polar lipids. ... 

Other polar phases, i.e., silicas with covalently bonded nitrile, nitro, amine, or diol groups, are valuable alternatives to silica. They are less polar (hence the mobile phase can be weaker) and have different selectivities. However, in most cases, they are used in the reversed-phase mode with aqueous mobile phases. Normal-phase applications of some importance are the separation of aromatics on nitro-derivatized phases, and of non-ionic surfactants on diol-derivatized phases. The theoretical plate numbers are usually lower than with non-derivatized sUica. Activity control (see Section 2.2.4 on troubleshooting of NP separations) is not necessary. The stability of the chemical bonding can be limited. 

Ethanol and choline glycerolipids were isolated from calf brain and beef heart lipids by PTLC using silica gel H plates. Pure ethanol amine and choline plasmalogens were obtained with a yield of 80% [74]. Four phosphohpid components in the purple membrane (Bacteriorhodopsin) of Halobacterium halobium were isolated and identified by PTLC. Separated phosphohpids were add-hydrolyzed and further analyzed by GC. Silica gel G pates were used to fractionate alkylglycerol according to the number of carbon atoms in the aliphatic moiety [24]. Sterol esters, wax esters, free sterols, and polar lipids in dogskin hpids were separated by PTLC. The fatty acid composition of each group was determined by GC. 

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