High-performance liquid chromatography (advances in packing materials)

Anderson, David J.

doi:10.1021/ac00108a032

Cited by 29 publications

(11 citation statements)

References 124 publications

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“…The surface is expected to exhibit negatively charged siloxy groups (≈5/nm 2 ) and a p K ranging from 5.8 to 7.2. The apparent range of silanol groups can be represented as two types (see refs −3 and 49 for discussion): “isolated” silanol groups are expected to be relatively acidic and may correlate with the “strongly reactive” silanols known to influence solute adsorption in liquid chromatography …”

Section: Resultsmentioning

confidence: 99%

Stability of Poly(ethylene glycol) Graft Coatings

1998

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Electrokinetic surface characterization is sensitive to both charge groups (pK and surface density) and neutral polymer coatings (molecular weight, surface density, grafting chemistry). It allows nondestructive, semiquantitative evaluation of coating stability, as regards alteration of the above parameters in relation to various environments. Characterization of surface electroosmosis versus pH (2 to 11) was used to evaluate poly(ethylene glycol) (PEG) coatings of biotechnical significance following a 3-week 22 °C exposure to 0.5 M sodium phosphate solutions of pH 4-11. The coatings involved epoxide-functionalized PEGs of Mr 3400 (E-PEG 3400) covalently grafted to aminosilane-modified fused quartz capillaries. Coatings made from PEGs with an epoxide group at one end (mE-PEG 5000) were stable at pH 4-11 whereas those made from PEGs with epoxide groups at both ends (diE-PEG 3400) were only stable at pH 4-9. During storage at pH 11 the latter exhibited time-dependent generation of surface negative charge groups of pK ≈ 5.3 and surface density (≈0.1/nm 2 ) similar to the PEG grafting density. The effect was significantly reduced by N2 purging of storage solutions to remove dissolved O2 and was mimicked by fresh, carboxyl difunctionalized PEG 3400 (diSPA-PEG 3400) coatings of similar surface density. The mE-, diE-, and diSPA-based coatings studied appeared to exhibit similar grafting densities (≈0.1/nm 2 ) and coating thicknesses (7 nm), suggesting grafting at only one end group. The factors responsible for limiting surface reaction by both end groups aided the ability of the diE-PEG coatings to secondarily tether (≈0.04/nm 2 ) a model amine-containing compound (n-propylamine) at the diE-PEG-coated quartz surface. Results are discussed in relation to practical applications.

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Section: Resultsmentioning

confidence: 99%

Stability of Poly(ethylene glycol) Graft Coatings

1998

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“…It is now possible to obtain less reactive stationary phases, called base-deactivated silica, which improve dramatically the peak shape of basic compounds [11,104]. It is now possible to obtain less reactive stationary phases, called base-deactivated silica, which improve dramatically the peak shape of basic compounds [11,104].…”

Section: Deactivated Supportsmentioning

confidence: 99%

Silica and other materials as supports in liquid chromatography. Chromatographic tests and their importance for evaluating these supports. Part I

et al. 2001

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Reversed-phase liquid chromatography (RP-HPLC) has become a powerful and widely employed technique in the separation and analysis of a great variety of compounds with different functionalities. The most common type of stationary phase for RP-HPLC consists of nonpolar, hydrophobic organic species (e.g., octyl, octadecyl) attached by siloxane bonds to the surface of a silica support. In the first part of this article, a description of the many beneficial properties that make porous silica the most employed support in RP-HPLC will be presented, starting from the synthesis of silica. It is noteworthy that the chromatographic properties of the final column are strictly correlated to the preparation type. A silica surface possesses a number of attractive properties, but also some drawbacks. Unreacted or residual silanols interact with basic compounds and can induced peak tailing, which means a loss in chromatographic performance. This problem has lead many manufactures to produce stationary phases with reduced silanol activity which improve dramatically the peak shape of basic compounds. In the second part of this review, different approaches are proposed to obtain less reactive stationary phases

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“…Silica-based materials such as glass and quartz are widely employed in a variety of analytical and separation methodologies. Examples include liquid chromatography, − analytical microparticle electrophoresis, , capillary electrophoresis, − and high-speed DNA analysis and sequencing. 7,11,12 The advantages and disadvantages of using such materials are well known. , The disadvantages primarily involve limited stability, variable performance, and strong solute adsorption (which reduces apparatus service life and causes phenomena such as peak tailing in chromatography and electrophoresis).…”

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confidence: 99%

Grafting Poly(ethylene glycol) Epoxide to Amino-Derivatized Quartz: Effect of Temperature and pH on Grafting Density

1996

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Microparticle capillary electrophoresis was used to characterize the surface of quartz capillaries grafted with the glycidyl ether of poly(ethylene glycol) (E-PEG). Site dissociation modeling of capillary electrokinetic behavior provided estimates of surface group pK and density, plus the distance (d) from the surface to the hydrodynamic plane of shear. Native quartz appeared to possess silanol groups of pK 3.6 and 6.9 whose surface densities varied with quartz treatment. Aminopropylsilane derivatization of quartz silanol groups in toluene yielded a coating which was stable (>6 h) at pH 10.3 and 60 °C. Aqueous grafting of E-PEG to this surface was relatively independent of pH (7.3-10.3) and reaction time (6-24 h) but was significantly influenced by reaction temperature (25-95 °C) and salt composition. PEG-grafted capillaries exhibited greatly reduced electroosmosis from pH 2 to 11. Significant grafting could be obtained under mild conditions (6 h, 35 °C, 0.4 M K(2)SO(4), pH 6.9). These results suggest that PEG chains increasingly extend normal to a surface as their grafting density increases, and that PEG conformation influences grafting density. The methods described should aid the use of PEG-coated surfaces in a variety of applications.

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High-performance liquid chromatography (advances in packing materials)

Cited by 29 publications

References 124 publications

Stability of Poly(ethylene glycol) Graft Coatings

Stability of Poly(ethylene glycol) Graft Coatings

Silica and other materials as supports in liquid chromatography. Chromatographic tests and their importance for evaluating these supports. Part I

Grafting Poly(ethylene glycol) Epoxide to Amino-Derivatized Quartz: Effect of Temperature and pH on Grafting Density

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