Surface silanol concentration change

TABLE 3-2. Surface Silanol Concentration Change after Chemical Modification [18]... 

Interaction of HPF with the silica surface could be analyzed for dried HPF/silica samples on the basis of changes in the FTIR spectra of the OH-stretching vibrations of free surface silanols at 3748 cm with increasing surface concentration (Cgpp j ) of protein (Figure 6.16). 

The change of the preparation media completely modifies the surface reactivity of the silica. The ammoximation results a convenient reaction for proUng the "defective state" and the silanol concentration. 

The most widely accepted condensation mechanism involves the attack of a nucleophilic deprotonated silanol on a neutral silicate species, as outlined earlier for the condensation in aqueous silicates [Eq. (5.4)]. This condensation mechanism pertains above the PZC (or lEP) of silica (pH > 2) because the surface silanols are deprotonated (i.e., they are negatively charged) and the mechanism changes with the charge on the silanol. Condensation between larger, more highly condensed species, which contain more acidic silanols, and smaller, less weakly branched species is favored. The condensation rate is maximized near neutral pH where significant concentrations of both protonated and deprotonated silanols exist. A minimum rate is observed near the PZC (or lEP). 

In a study utilizing SEC and fluorescence, retention time increased with increased concentration of Cu " which in this mode of HPLC would indicate that there had been a decrease in molecular size (3). It was also hypothesized that ionic interactions between the humic-metal complex and charged surfaces such as free silanol groups in the column packing may have also contributed to the increased retention time. In addition to changes in retention time, there was a decrease in peak area with increased copper concentration for both the UV and fluorescence chromatograms. This may have been due to an irreversible binding (in the time-scale of the separation) of copper-humic complexes to the stationary phase in the presence of increased Cu. ... 

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