Role of unreacted silanols in the adsorption properties of derivatized silica

Fóti, György; Kováts, Ervin sz.

doi:10.1016/s0021-9673(00)94290-0

Cited by 22 publications

(11 citation statements)

References 16 publications

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“…The practical usefulness of the RP-HPLC technique, however, seems to distract the chromatographer's attention from the theoretical problems that are left unsolved . For example, stationary phase stability and the relation between molecular stationary phase structure and chromatographic retention mechanism are still topics of discussion among stationary phase researchers. − Especially residual silanol functionalities, which remain at the silica surface after derivatization with alkylsilanes, have been the subject of investigation. − Apart from the solvophobic interactions between solutes and the nonpolar octadecyl phase, also the silanophilic interactions with residual silanols had to be taken into account to explain the observed chromatographic separation characteristics of silica-based alkylsilane phases.…”

Section: Introductionmentioning

confidence: 99%

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Fundamental Study of Residual Silanol Populations on Alkylsilane-Derivatized Silica Surfaces

et al. 1996

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Two commercially available reversed phases for high-performance liquid chromatography (one dimethyl-n-octadecylsilane phase and one di-isobutyl-n-octadecylsilane phase) and the native silica substrate were subjected to deuterium exchange in a mobile phase-like medium of acetonitrile and deuterium oxide (90/10, v/v). 29Si cross-polarization magic-angle-spinning (CP MAS) NMR was used to obtain information on the amounts and relaxation behavior of the internal silanols of the silica substrate, and the residual silanols of the alkylsilane-derivatized phases. Consequences for the correlation of silanol 29Si CP MAS NMR data and chromatography are discussed. Detection of deuterated silanol (SiOD) signals in 29Si CP MAS NMR of deuterium-exchanged phases depends on a transfer of magnetization (cross-polarization) from silane protons to silanol silicon atoms. It is concluded that a large portion of the residual silanol NMR signal of the phases stems from internal silanols and from silanols that are spatially very close to an alkylsilane attachment site. The former are considered chromatographically irrelevant while the latter are assumed to be inaccessible for analytes during the chromatographic separation process for reasons of steric constraints. One bulky di-isobutyl-n-octadecylsilane is capable of cross-polarizing proton magnetization to 0.8 residual surface silanols, whereas this is only 0.3 for the conventional octadecylsilane with dimethyl side groups. However, the lower surface concentration of bulky alkylsilanes leaves more space for free, unhindered silanols. The most important factor determining the relaxation behavior of the residual silanol NMR signal is the mobility of the octadecylsilane side chains, bulky silanes having the larger mobility quenching effect on residual silanols.

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Section: Introductionmentioning

confidence: 99%

“…Kováts et al . have demonstrated that, upon contact with acetonitrile mobile phases which contain D 2 O, all residual surface silanols are exchangeable, given enough time …”

Section: Introductionmentioning

confidence: 99%

Fundamental Study of Residual Silanol Populations on Alkylsilane-Derivatized Silica Surfaces

et al. 1996

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“…The silanol density of the silica gel after traditional procedure, i.e., drying and vacuuming as mentioned above is usually 8−9 µmol/m 2 [5] and every silanol group occupies an area of 0.2 nm 2 ; the average distance between two silanol groups is 0.5 nm, which means there are four to five hydroxyl groups each nm 2 ·Bonded Density % represents the ratio of the number of bonded organic groups to the number of hydroxyl groups that can potentially react.…”

Section: Burning Experiments-a Way To Express the Bonding Densitymentioning

confidence: 99%

Preparation and characterization of carbosilane dendrimer-bonded silica gel and its use in LC

2006

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Divergently synthesized carbosilane dendrimers generations 1(G1) and 2 (G2) with allyl end groups were bonded onto silica gel. Reactions between the dendrimers and acid-processed silica gel took place, with toluene reflux and organic base as catalyst. Chemically bonded silica gel was characterized by transmission electron microscopy (TEM), infrared (IR)，and other methods. The chemically modified silica gels were packed into high-pressure liquid chromatography (HPLC) column and their separation characters were evaluated. G2-bonded silica gel was effective in separating homologous compounds of alcohol, alkyl-substituted benzene, N-substituted benzene, metacrylic acid ester and phthalate.

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“…From spectroscopic evidence, it has been shown that the geminal and isolated silanol groups are the most reactive towards chlorosilanes [38,39]. From isotope exchange studies it has been shown that access to all unreacted surface silanols is sterically hindered to different extents by the dense graft [85]. Thus even at maximum surface bonding densities between 3 0 and 50 percent of the surface silanol groups will remain unreacted.…”

Section: Packingsmentioning

confidence: 99%

“…A number of Chromatographie test methods have been developed to determine some of the above properties (section 4.4). The concentration of unreacted silanol groups can also be determined by proton isotope exchange or by reaction with an organometallic reagent such as methyllithium [73,85,91,92]. The percent carbon loading for bonded phases is easily obtained by standard combustion analysis and is frequently quoted in the manufacturers literature [90].…”

Section: Packingsmentioning

confidence: 99%

The Column in Liquid Chromatography

Poole

1991

Chromatography Today

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Role of unreacted silanols in the adsorption properties of derivatized silica

Cited by 22 publications

References 16 publications

Fundamental Study of Residual Silanol Populations on Alkylsilane-Derivatized Silica Surfaces

Fundamental Study of Residual Silanol Populations on Alkylsilane-Derivatized Silica Surfaces

Preparation and characterization of carbosilane dendrimer-bonded silica gel and its use in LC

The Column in Liquid Chromatography

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