Bonded stationary phases polar functional group

Liquid-solid chromatography (LSC), sometimes referred to as normal phase or straight phase chromatography, is characterized by the use of an inorganic adsorbent or chemically bonded stationary phase with polar functional groups and a nonaqueous mobile phase... 

Normal-phase partition chromatography also uses a polar stationary phase and an nonpolar mobile phase such as n-hexane, methylene chloride, or chloroform. In this LC mode, however, the stationary phase is a bonded siloxane with a polar functional group, which in order of increasing polarity may be the cyano (-C2H4CN), diolC-CjHfiOCHzCHOHCHzOH), amino (-C d I N11,). or dimethylamino (-CsHeNfCHsiz) group. 

Bonded-phase column packings for use in normal-phase chromatography are available in which the stationary phase is a polar functional group chemically bonded onto the silica surface. One... 

In order to accomplish the desired separation, the selection of appropriate stationary phase and eluent system is imperative. The most commonly used stationary phases in normal-phase chromatography are either (a) inorganic adsorbents such as silica and alumina or (b) moderately polar chemically bonded phases having functional groups such as aminopropyl, cyanopropyl, nitrophenyl, and diol that are chemically bonded on the silica gel support [16]. Other phases that are designed for particular types of analytes have also... 

Before the development of reversed-phase bonded phases, normal-phase chromatography was the most popular separation technique. It relies on the interaction of analytes with polar functional groups on the surfooe of the stationary phase, which is strongest when nonpolar solvents are used as mobile phase. Previously, it was also called adsorption chromatography. However, the technique has expanded from the exclusive application of metal oxide adsorbents such as silica and alumina as stationary phases to the use of polar bonded phases. Thus the name adsorption chromatography has become too narrow. 

Similarly, other polar functional groups in the stationary phase can influence the selectivity of the separation as well. Thus one can find significant differences in selectivity between reversed-phase packings based on silica and those based on polymers. Also, reversed-phase bonded phases with polar functional groups incorporated in the ligand can exhibit significant differences in selectivity compared to their purely hydrophobic counterparts. 

In order to broaden the capabilities of the Pirkle concept, both polar and polarizable groups were introduced into the molecule. The most popular of this type of chiral stationary phase are the (R,R) Whelk-01 and the (S,S)Whelk-01 phases, the structures of which are shown below. These phases are more versatile and have a wider field of application than the phases previously described. The phases are covalently bonded to the silica and so they can be used with almost any type of solvent. However, they have been found to operate most effectively in the normal phase mode. It should be noted that the polarizable character of the aromatic ring is essential for the stationary phase to function well. As the Pirkle phases are generally available in both the (R) and (S) configurations, the reversal of the elution order of a pair of enantiomers is possible. This stationary phase was originally designed for the separation of the Naproxen enantiomers but has found a wide application to the separation of epoxides, alcohols, diols, amides, imides and carbamates. 

The hydrophilic modified stationary phases developed so far for thin-layer chromatography possess as functional groups amino, cyano, and diol residues. In each case polar functional groups are bonded via short-chain nonpolar spacers to the silica matrix. Therefore, a straight- or normal-phase and a reversed-phase retention mechanism can be applied by using such stationary phases. 

In the most common application of this separation mode, components are separated according to the number and nature of the polar functional groups (e.g., ester bonds, phosphate, hydroxyl, and amine groups) in lipid molecules. Since the head group of an individual lipid class predominantly determines the polar interactions with stationary phase, normal-phase HPLC separates a lipid extract solution into the lipid classes rather than into molecular species. 

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