Bonded stationary phases octyl group

Variations in retention and selectivity have been studied in cyano, phenyl, and octyl reversed bonded phase HPLC columns. The retention of toluene, phenol, aniline, and nitrobenzene in these columns has been measured using binary mixtures of water and methanol, acetonitrile, or tetrahydrofuran mobile phases in order to determine the relative contributions of proton donor-proton acceptor and dipole-dipole interactions in the retention process. Retention and selectivity in these columns were correlated with polar group selectivities of mobile-phase organic modifiers and the polarity of the bonded stationary phases. In spite of the prominent role of bonded phase volume and residual silanols in the retention process, each column exhibited some unique selectivities when used with different organic modifiers [84],... 

Only about 50% of the free silanols in silica are bonded in octyl and octadecyl stationary phases. These residual silanols contents is further reduced by a process called endcapping, in which hexamethyl and isobutyl groups are additionally introduced into the matrix. Endcapped columns offer better separation and retention in addition to reduced peak tailing. 

Dolinar found that the packing with chemically bonded octyl groups was the most suitable stationary phase for the separation of ergot alkaloids with a wide range of polarities (Fig.9.1). The separations obtained on an octadecyl column were similar (Fig.9.2). On a dimethylsilyl column (RP2) and a spherical octadecyl column (Spherisorb 0DS), the less polar alkaloids were not as well separated as on the above-mentioned columns however, the more polar alkaloids were... 

Mixed mode or zwitterionic siloxane-bonded phases have been prepared by cobonding hydrophobic ligands, such as octyl or octadecyl, with cationic, anionic or polar ligands, in a single stationary phase [99]. An alternative approach is to first bond a ligand with a reactive terminal group, such as a 3-aminopropyl group, that... 

R is usually octyl (CgHjy) or octadecyl (C18H37) and is the active site in the case of reversed-phase liquid chromatography (RPLC). The notation RP-18 means that the stationary phase is a siloxane-bonded silica with octadecyl groups on its surface. This stationary phase is nonpolar and thus is suitable for RPLC. 

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