Separation stationary phase

Fig. 2. Effect of silica pore structure on separation. Stationary phases are 10 LiChrospher SI 100, SI 00, SI 1000, and SI 4000 having 100, 500, 1000. and 4000 A mean pore diameter, respectively. Rowrate and inlet pressure are 5 ml/min and 125 bar, respectively. Sample components I, benzene 2. diphenyl 3, m-terphenyl 4, m-quaterphenyl 5, m ipiliiqiicphcnyl 6, m-sexiphenyl. (Cotiuesy of Merck AO.)...

Fio. 10. Effect of pressure programming on chromatographic separation. Stationary phase, nitrobenzyl-silica, SI 200 d, 35 /tm column, 50 x 2 mm eluent, n-hepune, temp., 23 C. Sample components 1. unretained 2, bromobenzene 3, toluene 4, naphthalene 5, anthracene 6, brasan 7, o,A-[Pg.50]

With the advent of improved column deactivation, elution of more polar analytes has become possible. For this type of analytes, columns coated with selectively separating stationary phases may provide the most rapid analysis. This is the background to the increasing demand for moderately polar and polar stationary phases. Users want universal columns, that is, columns that can solve a number of analytical tasks. For that purpose, tire new generation of stationary phases should include phases in which different types of functional groups such as phenyl and cyanopropyl are present simultaneously (48). 

Adsorption chromatography. This chromatographic technique is best known because of its use in the last century as a preparative method of separation. Stationary phases have made a lot of progress since Tswett. who used calcium carbonate or sugar. The separation of organic compounds on a thin layer of silica gel or alumina with solvent as a mobile phase are examples of this type of chromatography. Solutes bond to the stationary phase because of physisorption or chemisorption interactions. The physico-chemical parameter involved is the coefficient of adsorption. 

Over 100 stationary phases of various types have been described in the literature for packed columns, which are slowly being abandoned. However, for bonded phase capillary columns the choice of stationary phase is limited because the generation of the film at the surface of the column requires a different principle than impregnation. Generally, two families of compounds are used to modify the polarity polysiloxanes and polyethylene (silicones) glycols. Very special phases such as cyclodextrins can be used for enantiomeric separations. Stationary phases can be used between a minimum temperature under which equilibrium is too slow to occur and a maximum temperature above which degradation of the polymer occurs. The maximum temperature depends on the film thickness and the nature of the polymer. 

Actually, solid-phase extraction is used not only as a rough preliminary fractionation procedure. Prieto et al. described the complete fractionation of the total lipids from wheat into eight neutral lipid, two glycolipid, and four phospholipid classes in addition to PC and LPC, TV-acyl PE and A-acyl LPE were detected (37). However, two separate stationary phases (silica and aminopropyl) as well as seven different mobile phases were needed. Moreover, 14% crosscontamination of PC and LPC was observed, and the recovery of the phospholipids was limited to about 85%. Hence, SPE is a rapid and efficient technique for preliminary fractionation, but loses its advantages if more complex separations are tried. 

Component(s) Separated Stationary Phase Mobile Phase Composition Mode Ref. 

Compounds separated Stationary phase Mobile phase Ref. 

Substances separated Stationary phase Column temperature, °C Other details Ref. 

Compounds separated Stationary phase" Mobile phase Ref. 

Surfactants separated Stationary phase Developing system Visualizer Ref. 

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