Bonded phases preparation

Fio. 12. Graph illustrating the dependence of the logarithm of retention factor for aromatic hydrocarbons on the carbon load of octadecyl silica bonded phases prepared from Par-tisil with octadecyhrichlorosilane. Mobile phase methanol-water (70 30) eluitest A, benzene A, naphthalene , phenanthrene , anthracene O, pyrene. Reprinted with permission from Herndon t al. (70). 

Finally, other proposals include the introduction of an amine into the eluent so that, unlike in bonded phases, preparation of the amino phase takes place in situ. This competes advantageously in terms of degradation of the column, since with this procedure columns may be immediately repaired by recoating and therefore losses in performance are minimized and even avoided. 

Use of alkylamide phases, in which alkyl chains are attached to the silica surface via an alkylamide group, reduces interactions with free silanols, by an internal masking mechanism. Residual silanols interact by hydrogen bonding with the embedded amide groups and thus become less active toward analytes. The embedded polar amide groups lessen the hydrophobicity of these phases compared to that of C18 bonded phases prepared from the same silica. Improved peak shapes of ionizable compounds were reported and this stationary phase was successfully used under IPC conditions to analyze streptomycin and its dihydrostreptomycin derivative in food... 

Figure 4.7. CP-MAS NMR spectra of a series of octadecylsiloxane-bonded phases prepared by different reaction mechanisms and the silica substrate. 1 = Porous silica (structural elements Q -85 to -115 ppm) 2 = monomeric phase prepared with octadecyldimethylchlorosUane (M 15 to 0 ppm) 3 = polymeric phase prepared by the solution method with octadecylmethyldichlorosilane (D -5 to -25 ppm) 4 = polymeric phase prepared by the solution method with octadecyltrichlorosilane T 5 to -70 ppm) and 5 = surface polymerized phase using octadecyltrichlorosilane. (Adapted from ref. [110]. American Chemical Society).

The higher surface coverage available with polyfunctional silanes may have an advantage with respect to the hydrolytic stability of the packing, but the results ate not clearcut. At acidic pH, a reduced rate of hydrolysis was observed for Cig-type bonded phases prepared from di- and trifunctional silanes (9). 

Bonded Phases. Substrate-bond hydrocarbon coatings for high pressure Hquid chromatography (hplc) and flash chromatography are prepared from octyltrialkoxysilanes and other long-chain alkyltrialkoxysilanes (see Chromatography). 

Silylation reactions have been widely used to prepare bonded phases. The... 

The drawback of the described adsorbents is the leakage of the bonded phase that may occur after the change of eluent or temperature of operation when the equilibrium of the polymer adsorption is disturbed. In order to prepare a more stable support Dulout et al. [31] introduced the treatment of porous silica with PEO, poly-lV-vinylpyrrolidone or polyvinylalcohol solution followed by a second treatment with an aqueous solution of a protein whose molecular weight was lower than that of the proteins to be separated. Possibly, displacement of the weakly adsorbed coils by the stronger interacting proteins produce an additional shrouding of the polymer-coated supports. After the weakly adsorbed portion was replaced, the stability of the mixed adsorption layer was higher. 

The suspension of influenza virus, strain A/X-53, was separated from the constituents of alantoic fluid by preparative size exclusion chromatography on a 10 x 120 cm column. The hemo-agglutination method revealed an elevated level (93%) of viral activity. The leakage of the bonded phases can be more efficiently minimized, however, with the use of positively charged polymers. 

The preparation of the lemon juice for analysis was simple, a sample of the lemon juice was filtered and 5 pi placed on the column. The separation was carried out on a novel bonded phase carrying amino-propyl groups. The separation obtained is shown in figure 11. 

Reversed-phase PLC precoated plates are based on silica gel matrices with chemical modifications in such a manner that the accessible polar, hydrophilic silanol groups at the silica gel surface are replaced by nonpolar, hydrophobic alkyl chains via silicon-carbon bonds. For preparative purposes, up to now only PLC precoated RP plates with C-18 modification are available. This abbreviation is often also designated as RP-18, meaning that an octadecyl alkyl chain is chemically bonded to the silica gel surface. 

Bonded phases have been prepared by other general methods besides those indicated so far [64-66]. Reaction of silica with an alcohol or isocyanate resulted in the formation of silicate esters (estersils), but these phases were too hydrolytically unstable to be generally useful. Bonded phases with an Sl-R or Sl-NHR structure are more hydrolytically stable than the estersils but... 

REAGENTS USED IN THE PREPARATION OF OCTADECYLSILOXANE BONDED PHASES IDENTIFIED BY ACID OR BASE CLEAVAGE... 

Sllylation, preparation of bonded phases (LC) 324 Simplex optimization selectivity (LC) 478 temperature program (GC) 56 Single column ion chroBatography 434, 438 Sintered glass layer (TLC) 671 Size-exclusion chroBatography 439... 

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