Silica surface controversies, strong adsorption sites, their blockage and removal. Part II

Nawrocki, J.

doi:10.1007/bf02274571

Cited by 74 publications

(40 citation statements)

References 149 publications

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“…This parameter depends on the conditions of synthesis but also on the raw materials used (e.g., water glass, silica sol, sulfuric acid, or ammonia), which are intrinsically contaminated with trace amounts of metal ions. Conventional silica gel contains 0.1 to 0.3% of metal impurities, although recent articles deal with trace metal impurity levels of about 10 ppm [43]. Obviously, in many cases these low impurity levels may differ from batch to batch at the same manufacturer.…”

Section: Surface Purity Of Supportmentioning

confidence: 98%

“…On the other hand, hydrochloric acid removes metal impurities quite efficiently from the silica hydrogels [46]. Ethylenediaminetetraacetic acid (EDTA) has been claimed to remove all the metallic impurities [43], although others have found acid washing more effective than EDTA [42 -44]. The cleaning of silica gel adsorbents has been shown to increase the coverage density of alkylsilyl ligands and to improve the chromatographic properties of resulting packings.…”

Section: Surface Purity Of Supportmentioning

confidence: 99%

“…All available supports differ in the presence and concentration of metal impurities [8,37,41,43,44]. This parameter depends on the conditions of synthesis but also on the raw materials used (e.g., water glass, silica sol, sulfuric acid, or ammonia), which are intrinsically contaminated with trace amounts of metal ions.…”

Section: Surface Purity Of Supportmentioning

confidence: 99%

See 2 more Smart Citations

Survey and Trends in the Preparation of Chemically Bonded Silica Phases for Liquid Chromatographic Analysis

Buszewski¹,

Jezierska

Wełniak

et al. 1998

J. High Resol. Chromatogr.

145

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Section: Surface Purity Of Supportmentioning

confidence: 98%

Section: Surface Purity Of Supportmentioning

confidence: 99%

See 1 more Smart Citation

Survey and Trends in the Preparation of Chemically Bonded Silica Phases for Liquid Chromatographic Analysis

Buszewski¹,

Jezierska

Wełniak

et al. 1998

J. High Resol. Chromatogr.

145

View full text Add to dashboard Cite

“…Additionally, capillary wall activity toward basic compounds has been one of the most troublesome difficulties encountered in current CE practice. While for the most part highly acidic isolated silanols have been generally considered the strongest adsorption sites in LC and CE, metallic impurities even at the trace level may be an additional source of acidic species on the silica surface [6][7][8]. It has been postulated that trace metals significantly increase the acidity of adjacent silanol groups [6,7].…”

Section: Introductionmentioning

confidence: 98%

The effect of conditioning of fused‐silica capillaries on their electrophoretic performance

Gómez

Sandoval

2008

Electrophoresis

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In CE practice, conditioning of the capillary tube with strong base, acid, or both in sequence, has been recognized as essential to obtain reasonable precision in electroosmotic mobility (EOM), and consequently, in the migration times of analytes. This report focuses on the comparative study of three different approaches for capillary conditioning: etching with HF, etching with NaOH, and leaching with HCl after NaOH treatment. EOM-based measurements, including the hysteresis effect that characterizes the dependence of EOM with pH, were used to evaluate the conditioned silica surface. Additionally, indirect inspection of the conditioned surface was carried out by examining the electrophoretic profile of the cationic probe Ru(bpy)(3) (2+), known to strongly interact with the ionized silica surface while displaying no significant acid-base activity. It was shown that, once conditioned and prior to any CE measurement, extensive rinse of the capillary with the running electrolyte at high flow rate was essential to attain relatively rapid re-equilibration of the tube with the fluid. Insufficient rinse with the running electrolyte would result in negatively biased EOM measurements and significant drift in migration times. It was also established that relatively high flow rates of 1 M NaOH conditioning solution (4-5 column volumes per minute) was required to attain capillaries with reproducible electrophoretic performance within a reasonable conditioning time (typically, 1 h). In addition to relatively more extensive rehydroxylation of the silica surface, evidenced by the highest EOM values obtained, the sequential use of NaOH-etching and HCl-leaching provided better precision than HF-etching or NaOH-etching alone.

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“…Estes suportes têm estrutura semelhante a da sílica onde a superfície é recoberta por grupos siloxanos ( Si-O-Si) e silanóis (Si-OH) 3 . Tais grupos apresentam características adsortivas, pois enquanto um funciona como doador de próton o outro funciona como aceptor.…”

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Estudo da Determinação dos Grupos Silanóis ( º Si-OH) em Sílica: Aplicação à Materiais de Recheio Utilizados em Cromatografia Gasosa

Pizzutti¹,

Schwerz²,

Viaro³

et al. 1997

Quím. Nova

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  Si-OH) in silica as well as in coated chromatographic supports for use in packedcolumn Gas Chromatography. After adsorption of 10 µ µ µ µ µg/mL methylene blue, centrifuging action and filtration, the absorbance of the solution was inversely proportional to the silanol quantity. The difference between the absorbance of the pure solution and that of the solid -free filtrate was related to the silica weight, yielding a quantitative analysis of these groups.Keywords: methylene blue; silanol group; UV-Vis spectrophotometry. ARTIGO INTRODUÇÃOA potencialidade das cromatografias gasosa e líquida como técnicas de separação, identificação e subsequente quantificação já é bem estabelecida. O poder de separação de ambas as técnicas está relacionado à coluna cromatográfica e ao material nela contido. No caso de cromatografia gasosa com colunas recheadas, o referido material de recheio pode ser um sólido finamente dividido (cromatografia gás-sólido) ou um líquido pouco volátil recobrindo um suporte sólido (cromatografia gás-líquido)1 . Quando o material da coluna é um sólido, a separação baseia-se na adsorção física e química das substâncias da amostra no sólido, o que constitui uma limitação do método já que a adsorção, que pode ser irreversível, produz picos com caudas, as vezes demonstrando uma pobre separação que dificulta a análise quantitativa. Quando a fase estacionária é um líquido, ela solubiliza as substâncias presentes na amostra de maneira seletiva para que as mesmas não eluam da coluna sem a devida separação. A separação, neste caso, baseia-se nas diferentes solubilidades das substâncias na fase estacionária e nas suas diferentes volatilidades 2 . Na prática da Química Analítica, quando se utiliza a cromatografia gás-líquido com colunas recheadas, o conhecimento do suporte sólido empregado é de extrema importância pois, na maioria das vezes, este é o responsável pelos problemas que acontecem nas separações.O suporte mais comumente utilizado em cromatografia gasosa é proveniente de diatomita, material obtido do esqueleto de algas diatomáceas (terras diatomáceas ou Kieselgur). Estes suportes têm estrutura semelhante a da sílica onde a superfície é recoberta por grupos siloxanos ( Si-O-Si) e silanóis (Si-OH) 3 . Tais grupos apresentam características adsortivas, pois enquanto um funciona como doador de próton o outro funciona como aceptor. Estas propriedades adsortivas são indesejáveis e por isso, muitas vezes é necessário que o suporte sofra processos de desativação 4 de forma a tornar a sua superfície mais apolar e não causar problemas de adsorção com moléculas da amostra.Sabe-se que a sílica gel completamente hidrolizada apresenta uma concentração de silanóis de 8-9 µmol OH/m 2 que podem ser do tipo isolado, vicinal e geminal 4 . Além disso, há os grupos siloxanos que diferem dos demais na reatividade química e no comportamento adsortivo. Estudos mostraram que o grupo silanol geminal (=Si-(OH) 2 ) é o mais reativo das espécies de superfície 5 .Devido ao sério problema de adsorção causado por estes grupos, ...

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Silica surface controversies, strong adsorption sites, their blockage and removal. Part II

Cited by 74 publications

References 149 publications

Survey and Trends in the Preparation of Chemically Bonded Silica Phases for Liquid Chromatographic Analysis

Survey and Trends in the Preparation of Chemically Bonded Silica Phases for Liquid Chromatographic Analysis

The effect of conditioning of fused‐silica capillaries on their electrophoretic performance

Estudo da Determinação dos Grupos Silanóis ( º Si-OH) em Sílica: Aplicação à Materiais de Recheio Utilizados em Cromatografia Gasosa

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