Octadecylsilyl-bonded silica

In order to determine the applicability of retention indices, based on the alkyl arylketone scale, as the basis of a reproducible method of reporting retentions, the separation of 10 barbiturates and a set of column test compounds were examined on an octadecylsilyl bonded silica (ODS-Hypersil) column with methanol-buffer of pH 8.5 as eluent [100]. The effects on the capacity factors and retention indices, on changing the eluent composition, pH, ionic strengthened temperature, showed that the retention indices of the barbiturates were much less susceptible to minor changes in the eluent than the capacity factors. 

Figure 7.9 Reaction scheme illustrating the preparation of octadecylsilyl-bonded silica.

The most common packing used in the purification of biologically important species has been octadecylsilyl bonded silica (ODS, Cis). ODS silicas are available from a number of companies either in free form or as... 

Nimura, N., Itoh, H., Kinoshita, T., Nagae, N., Nomura, M. (1991). Fast protein separation by reversed-phase high-performance liquid-chromatography on octadecylsilyl-bonded non-porous silica-gel — effect of particle-size of column packing on column efficiency. J. Chromatogr. 585(2), 207-211. 

ODS—Octadecylsilyl bonded phase material or column in which the material bound to silica is an 18-carbon saturated hydrocarbon chain. See Ci8.)... 

Stationary phases. Five stationary phases from Shandon (Runcorn, Cheslvie, GB) were used they were spherical microparticules of 5 pm mean diameter. The four bonded silicas were manufactured from the same parent silica (Hypersil) and possess a monolayer coverage of trimethylsilyl (SAS Hypersil), dimethyloctylsilyl (MOS Hypersil), octadecylsilyl (ODS Hypersil) and cyanopropylsllyl (CPS Hypersil) groups. Their physicochemical properties are listed in Table II. The elemental analysis of carbon (SIC), corrected for the SIC value of naked silica, enables to estimate the surface concentration of the substituent (r ) with ... 

Simple and comprehensive 2D HPLC was reported in a reversed-phase mode using monolithic silica columns for the 2nd-D separation (Tanaka et al., 2004). Every fraction from the lst-D column, 15cm long (4.6 mm i.d.), packed with fluoroalkylsilyl-bonded (FR) silica particles (5 pm), was subjected to the separation in the 2nd-D using one or two octadecylsilylated (Cig) monolithic silica columns (4.6 mm i.d., 3 cm). Monolithic silica columns in the 2nd-D were eluted at a flow rate of up to lOmL/min with separation time of 30 s that provides fractionation every 15-30s for the lst-D, which is operated near the optimum flow rate of 0.4-0.8 mL/min. The 2D-HPLC systems were assembled, as shown in Fig. 7.6, so that the sample loops of the 2nd-D injectors were back flushed to minimize band broadening. 

Values of aj = Ink- for various functional groups, on silica with the bonded octadecylsilyl groups at 50°C, using ethanol-water (35 65) eluent... 

Figure 14. Correlation between the experimental and calculated values of In k of cardiac glycosides and steroid hormones, at 50°C on silica gel with bonded octadecylsilyl groups from eluent ethanol water (35 65). The numbers correspond the compounds on Fig. 13.

Changes in the differential enthalpy of adsorption (—AH) of some cardiac glycosides and steroid hormones from aqueous ethanol used as the eluent, on silica gel with bonded octadecylsilyl groups... 

The contributions of steroids functional groups to the differential entropy of adsorption from ethanol-water eluents ( — AH i) on silica with bonded octadecylsilyl groups... 

Excellent separation can be achieved by using silica with bonded octadecylsilyl groups and optimized composition of alcohol - hydrocarbon eluent [16]. At separation of Ceo and C70 on fj. Bondapak 10 C18 from mobile phase containing 70% of n-hexane and 30% of isopropanol the selectivity was 1.91 (Fig. 3 a.). For the detection UV detector at 254 nm can be used. In this case the oxide of Ceo can be separated from Ceo with the selectivity 1.18 and the oxide is eluted before Ceo owing to more strong interaction of Ceo oxide with alcohol in eluent. The determination of fullerene oxides is quite important in analysis of the purity of fullerenes. 

The materials introduced initially, and still used most often, were silicas with apolar long chain alkylgroups (e.g., octadecylsilyl (ODS) groups) chemically bonded to the surface. Thus, the materials were intended for reversed phase chromatography (cf.. Fig. 4.4.7). Since then various materials have been introduced with bonded short chains carrying polar groups, e.g., nitril, amino, dimethylamino, dihydroxy, nitro. 

Reversed-phase chromatography is perhaps the most widely used chromatographic method. It was first developed by Howard and Martin (1950) to separate fatty acids by using a polar eluent (mobile phase) and a nonpolar stationary phase that consisted of paraffin oil and octane. Today the stationary phase consists of a liquid that is chemically bonded to a support. For example, the column packings contain octadecylsilyl (Cig), octylsilyl (Cg), butylsilyl (C4), or propylsUyl (C3), which are bonded to silica supports having various pore sizes (e.g., 100, 300, and 500 A) and particle sizes (e.g., 5 and 10 pm). The extent of retention of a molecule depends on the number, size, and stereochemistry of its hydrophobic (e.g., alkyl) and hydrophilic (e.g., ionic) groups. 

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