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

Nawrocki, J.

doi:10.1007/bf02274570

Cited by 149 publications

(75 citation statements)

References 162 publications

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“…To explain the role of the silica substrate of the column in controlling the EOF, the hypothesis of Tanabe et al [33][34][35] can be applied. This model was developed to describe the surface acidity caused by the charge distribution in binary metal oxides.…”

Section: Discussion On Influence Of Surface Treatment On Eofmentioning

confidence: 99%

The influence of surface treatments on the electroosmotic flow in micellar electrokinetic capillary chromatography

Claessens

Cramers

1992

Chromatographia

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Section: Discussion On Influence Of Surface Treatment On Eofmentioning

confidence: 99%

The influence of surface treatments on the electroosmotic flow in micellar electrokinetic capillary chromatography

Claessens

Cramers

1992

Chromatographia

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“…The acidity of silanols can be increased by neighboring metal ions in the silica matrix. [41][42][43][44] These acidic silanols are probably responsible for the ionic interaction at pH 3. However, on the Caltrex ® columns they will be effectively shielded by the large calixarenes and the ionic interaction at the silanols is suppressed.…”

Section: Ionic Selectivitymentioning

confidence: 99%

Selectivity of Calixarene-bonded Silica-phases in HPLC: Description of Special Characteristics with a Multiple Term Linear Equation at Two Different pH-Values

2008

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Calixarenes are supramolecules consisting of phenol units linked via methylene bridges. Covalently bonded to a silica gel, they act as a reversed-phase. Their application as a stationary phase in HPLC has been recently reviewed. 1Additionally to the well known interactions of alkyl-bonded silicas, they can give rise to retention by forming complexes [2][3][4][5][6][7][8][9][10] and by providing p-p-interactions 3,7,11,12 or p-electron-transfer. 7-12For that reason, calixarene-bonded phases exhibit special selectivities. It is obvious that differences of selectivities can be distinct between different kinds of calixarene-bonded phases and especially between calixarene-bonded phases and common C18-phases. In order to select suitable columns for new separation problems, it would be beneficial to numerically describe the retention characteristics and the selectivity of each column. Numerous works have been done in that field and mathematical models relating the retention factor to properties of the column, the solute and the mobile phase were developed. [13][14][15][16][17][18][19][20] The retention has been related to physicochemical parameters or, in more empiric ways, to parameters derived from retention data.The retention and selectivity characteristics of novel calixarene-bonded HPLC-phases are described here. Therefore a multiple term equation has been used. The mechanisms of retention are estimated with its single parameters. Theory Mathematical modelsA linear equation describing solute retention was introduced by Snyder:Here the retention of a solute ln k¢ is defined by its retention in pure water, a solute specific value S and the volume fraction of organic modifier f. Yet the equations applicability is limited to a range of 0.2 -0.8f. Equations valid over the whole range of mobile phase composition were described by Schoenmakers et al. 14,15 and by Bosch, Bou and Rosés. 16 Schoenmakers quadratic equation uses factors based on Hildebrands solubility parameter. 21 The factors can be calculated from physical parameters.The model of Rosés et al. is based on the Dimroth Reichardt polarity parameter ET(30). 22 This parameter had been related to log k¢ by Johnson et al. 17 and has been found to give better linear relations to log k¢ than the volume fraction of methanol. Under the assumption that stationary phase polarity is independent of mobile phase composition, Rosés model predicts retention factors by use of two variables. This leads to a simple equation which can be handled easily. Pappa-Louisi et al.23 studied various two-and three-parameter-models concerning their applicability to predict ln k¢. The best predictions could be given by a three-parameter-model, while the two-parametermodels gave comparatively poor results. They pointed out that generally the largest errors occur for predicting retention times of late eluting substances at low modifier concentrations and that predictions deteriorate if the observed modifier range expands.However, although such "compact" systems include only a small number of p...

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“…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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Silica surface controversies, strong adsorption sites, their blockage and removal. Part I

Cited by 149 publications

References 162 publications

The influence of surface treatments on the electroosmotic flow in micellar electrokinetic capillary chromatography

The influence of surface treatments on the electroosmotic flow in micellar electrokinetic capillary chromatography

Selectivity of Calixarene-bonded Silica-phases in HPLC: Description of Special Characteristics with a Multiple Term Linear Equation at Two Different pH-Values

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

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