Phenyl-bonded silica

Cation-exchanger. Phenyl-bonded silica gel is suspended in chlorosulfonic acid-acetone and boiled under reflux. After filtration and washing with acetone and dilute HC1, the sulfonated gel is then converted into a suitable salt form ... 

Figure 3.10 Selectivity of phenyl-bonded silica gel compared with ODS silica gel.

Columns. ODS-silica, YMC ODS, 15 cm x 6.0 mm i.d., phenyl-bonded silica gel, YMC phenyl, 10 cm x 6.0 mm i.d. eluent, aqueous acetonitrile. Compounds, x, polycyclic aromatic hydrocarbons O, alkylbenzenes O,polychlorobenzenes +, alkanols A, alkanes 1, benzene 2, benzopyrene 3, toluene 4, heptylbenzene 5, hexachlorobenzene 6, hexanol 7, tetra-decanol 8, pentane and 9, octane. 

Since the 1970s numerous HPLC methods using lEC, RP and ion-pair chromatography have been proposed. In the last years, RP chromatography has become the most used method, thanks to its simplicity, sensitivity, and compatibility with different detection techniques. The stationary phases usually used are C18 or phenyl-bonded silica-based phases. More recently, alternative stationary phases, such as polar-embedded, polar endcapped, and perfluorinated phases, have been successfully tested for folate analysis [577]. The mobile phase is usually a mixture of phosphate or acetate buffer and acetonitrile or methanol. 

Tire preferred type of reversed-phase sorbents is Cjg bonded silica (Table 29.4). Using this reversed-phase sorbent, ion-pair separation of lincomycin (154), spiramycin (138), and tylosin (145) residues has also been reported through use of octanesulfonate, heptanesulfonate, and tetrabutylammonium pairing ions, respectively. Phenyl-bonded silica or polymeric stationary phases have also been described for the separation of tilmicosin (133) and lincomycin (146) residues, respectively. 

Liquid chromatographic separation of sedatives and -blockers is usually performed using reversed-phase columns. The preferred type of reversed-phase material is Cig-bonded silica (Table 29.16), but phenyl-bonded silica has also been employed for separation of xylazine and its major metabolite (525). Ion-pair liquid chromatography has also been suggested for separation of carazolol and xylazine residues, by addition to the mobile phase of dodecyl sulfate (522) or heptanesulfonate (520) pairing ions, respectively. 

T. Hanai and J. Hubert, Selectivity of phenyl-bonded silica gel, /. Chromatogr. 291 (1984), 81-89. 

Figure 12.11 Sample chromatogram for separation of pilocarpine (P), isojnlocarpine (I) and pilocarpic acid (A). A phenyl-bonded silica was used with mobile phase of acetonitrile-aqueous buffer (3 90 v/v), (pH 2.5).

Porous graphitized carbon > polymers made from cross-linked styrene/divinylben-zene > n-octadecyl (C18) bonded silicas > n-octyl (C8) bonded silicas > phenyl-bonded silicas > n-butyl (C4) bonded silicas > n-propylcyano-bonded silicas > diol-bonded silicas... 

LC-Ph Phenyl-bonded silica Nonpolar to moderately polar... 

Cahours, X., et al.. Fast separation of nucleosides by capillary electrochromatography on non-endcapped phenyl-bonded silica phase using short-end injection method, J. High Resol. Chromatogr., 23, 138, 2000. 

The most common reverse-phase sorbent used in SPE is C-18 silica with various particle sizes (40-70 j,m) and pore sizes (55-125 A). Other reverse-phase sorbents include C-8, C-4, C-2, cyclohexyl, and phenyl-bonded silica, as well as polymeric sorbents such as polystyrene-divinylbenzene (PS-DVB) and graphitized carbon. 

Flavonol isomers, which differ only in the position of hydroxyl group on their chemical structures, showed different chromatographic behaviors. Liu et al. ° separated three flavonol isomers (3-hydroxyflavone, 6-hydro-xyflavone, and 7-hydroxyflavone) by a lab-constructed packed column SFC system with carbon dioxide modified with ethanol containing 0.5% (VAO phosphoric acid as the mobile phase. The effects of temperature, pressure, composition of mobile phase, and packed-column type on the separation were studied. It was indicated that the addition of phosphoric acid to the mobile phase enabled flavonol isomers to be eluted from the column. It was also shown that a phenyl-bonded silica column was better and the ODS column was not as effective for the isomer separation. Increasing pressure shortened the retention time of each compound, with good resolution, and higher temperature led to longer retention times, and even the loss of the bioactivities of these components. Under selected conditions, the separation of these isomers was very satisfactory, as illustrated in Fig. 2. 

These materials are suitable for RP-TLC owing to their lipophilic properties. The commonly used RP layers consist of dimethyl-(RP-2), octyl-(RP-8), octadecyl-(RP-18), and phenyl-bonded silica gel, type 60, with different mean particle sizes and particle size distributions. Recently, C30-modified silica gel was proposed for the separation of tocopherol homologues. 

---