Reverse phase chromatography octyl

In reverse-phase chromatography, which is the more commonly encountered form of HPLC, the stationary phase is nonpolar and the mobile phase is polar. The most common nonpolar stationary phases use an organochlorosilane for which the R group is an -octyl (Cg) or -octyldecyl (Cig) hydrocarbon chain. Most reverse-phase separations are carried out using a buffered aqueous solution as a polar mobile phase. Because the silica substrate is subject to hydrolysis in basic solutions, the pH of the mobile phase must be less than 7.5. 

If solutes dissolve only in nonpolar or weakly polar solvents, the decision tree suggests that we try reversed-phase chromatography. Our choices include bonded phases containing octadecyl (CJg), octyl, butyl, ethyl, methyl, phenyl, and cyano groups. 

Kennedy 1990). This form of chromatography uses hydrophilic gel-based material as a matrix, which has been partially substituted on the surface with non-polar alkyl (e.g., methyl or octyl) or aryl (e.g., phenyl) groups (Table 4-3). Similar materials are used in reverse-phase chromatography (RPC), but the degree of substitution used for HIC chromatography (10-50 pmol ml-1 gel) is much lower than that used in RPC (100-500 pmol ml-1 gel). The solvent used for elution in HIC is low ionic strength buffer and not organic solvents which are characteristic of RPC. 

Fig. 2 Variation of the available capaeity Cj as a function of the solute concentration in the mobile-phase Q (logarithm scales). In the case of reversed-phase chromatography, the stationary phase is n-octyl-bonded silica Lichroprep R.R8 with 11.6% of carbon, the mobile phases are water-methanol mixtures, and the solute is phenol. 

Ion pairing extends reversed-phase chromatography to the separation of ionic solutes, which are generally unretained by hydrophobic stationary phases. A hydrophobic counterion, such as octyl sulfonate or tetrabutyl ammonium ion, is added to solution and forms a coulombic ion pair with oppositely charged... 

Reversed-phase chromatography is now widely used for the fractionation of biological molecules. The technique is based on the use of a non-polar stationary phase and a polar mobile phase. The stationary phase is usually made of a hydrocarbonaceous layer, either n-octyl. Cfl, or n-octadecyl, Cib, ligands, chemically bonded to the surface of a silica matrix via siloxane bonds. Separation Is achieved by exploiting the difference in the hydrophobic properties of the molecules. 

As is apparent from Table II and for the reasons indicated above, reverse-phase chromatography has been used mainly for the separation of the more-polar retinoids, although an excellent separation of a mixture of retinyl esters has been obtained on an octyl reverse-phase column (Ross, 1981 Fig. 4). While straight-phase chromatography offers better resolution of the isomers of retinol and retinaldehyde (Stancher and Zonta, 1982a), reverse-phase HPLC is capable of partially separating a complex mixture of the more polar retinoic acid isomers (McKenzie et al., 1978a Fig. 5), as well as the isomers of the metabolites of... 

Several improved stationary phase materials have been synthesized for reversed-phase liquid chromatography. One material is vinyl alcohol copolymer gel. This stationary phase is quite polar and chemically very stable however, it demonstrated a strong retention capacity for polycyclic aromatic hydrocarbons.45 9 Although stable octadecyl- and octyl-bonded silica gels have been synthesized from pure silica gel50,51 and are now commercially available, such an optimization system has not yet been built. Further experiments are required to elucidate the retention mechanism, and to systematize it within the context of instrumentation. 

At present, liquid chromatography is the method of choice for determining residues of quinolone antibacterials in edible animal products (Table 29.6). Separation is generally carried out on nonpolar reversed-phase columns containing octadecyl, octyl, phenyl, or polymeric sorbents. Either methanol or acetonitrile... 

At present, liquid chromatography has become the most widely used technique for determining anticoccidial drugs in edible animal products (Table 29.11). The separation of these drugs is generally done on nonpolar reversed-phase columns (octadecyl, octyl and phenyl), the preferred type being the octadecyl bonded silica. However, polar (389, 390, 392, 398, 400) columns have also been used for the determination of the polyether antibiotics in edible animal products. 

The use of reversed-phase liquid chromatography is growing in applications for separating mixtures of peptides. In this type of chromatography, the stationary phase is nonpolar, whereas the mobile phase is polar. The stationary phase is normally porous silica with bonded n-alkyl chains, mainly octadecyl but also octyl, hexyl, butyl, and propyl chains. 

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