Joseph J. Pesek

Chemically modified surfaces

Opening Remarks - Ivan Leigh. Plenary Lecture - Conversion of Oxide Surfaces to Hydride Surfaces - Joseph J. Pesek. New Synthetic Methodology for Grafting at Polymer Surfaces - David E. Bergbreiter. The Synthesis and Properties of Mutually Interpenetrating Organic-Inorganic Networks - Bruce M. Novak, Mark W. Ellsworth and Celine Verrier. The Physisorption and Condensation of Aminosilanes on Silica Gel - Karl. C. Vrancken, P. van Der Woort, K. Possemiers, P. Grobet and E.F. Vansant. Extraordinary Thermal Stabilization of Enzymes Through Surface Attachment by Covalently-Bound Phospholipids - K.M.R. Kallury and M. Thompson. Ellipsometry, X-Ray Photoelectron Spectroscopy and Surface Plasmon Resonance as Techniques for the Study of Chemically Modified Surfaces - John D. Brennan, R.F. DeBono, Krishna M.R. Kallury and Ulrich J. Krull. Spectroscopy of Evaporated and Langmuir-Blodgett Films of Gadolinium Bisphthalocyanine on Metal Surfaces - B. Berno, R. Aroca and A. Nazri. Surface Chemistry of Microporous Manganese Oxides - S.L. Suib, H. Cao and W.S. Willis. High Temperature Sorbents for Oxygen Supported on Platinum Modified Zeolites - Pramod K. Sharma. Catalysts for Environmental Control - Ronald M. Heck and Robert J. Farrauto. Mechanism of Surfactant-Assisted Increase in Coal Liquefaction Yields - Gregory S. Hickey and Pramod K. Sharma. The Effect of Glass Fibre Surface Coatings on Fibre Strengths and the Distribution of Flaws - J.A. Gomez and J.A. Kilgour. Stability and Reactivity of Dimethylethoxysilane - Richard E. Johnson and Douglas I. Ford. Molecular Dynamics of Liquid Chromatography: Chain and Solvent Structure Visualization - Mark R. Schure. 2H and 13C NMR Studies of Reversed Phase Liquid Chromatographic Stationary Phases: Solvation and Temperature Effects - K.B. Sentell, D.M. Bliesner and S.T. Shearer. Spectroscopic and Chromatographic Characterization of a Self-Assembled Monolayer as a Stationary Phase - M.J. Wirth and H.O. Fatunmbi. FTIR Study of Adsorption at the Silica / Solution Interface: Interaction of Surface Sites with Carbonyl Groups - J.M. Berquier.

Analysis of hydrophilic metabolites by high-performance liquid chromatography–mass spectrometry using a silica hydride-based stationary phase

A novel silica hydride-based stationary phase was used to evaluate the retention behavior in the aqueous normal-phase (ANP) mode of standards representing three classes of metabolites. The effects on retention behavior of amino acids, carbohydrates and small organic acids were examined by altering the column temperature, and by adding different additives to both the mobile phase and sample solvent. Gradient mode results revealed the repeatability of retention times to be very stable for these compound classes. At both 15 and 30 degrees C, excellent RSD values were obtained with less than 1% variation for over 50 injections of an amino acid mixture. The ability to separate the 19 nonderivatized amino acid standards, organic acids and carbohydrates was demonstrated as well as the potential for this material to separate polar metabolites in complex fluids such as urine.

Synthesis, Characterization and Applications of Hydride-Based Surface Materials for HPLC, HPCE and Electrochromatography

Abstract The chemical modification method based on the silanization of an oxide surface to a hydride intermediate followed by hydrosilation with an organic molecule containing a terminal olefin is reviewed. The resulting bonded organic moiety is attached to the surface via a direct Si-C bond which leads to high stability. The method has been more extensively applied to silica surfaces for the production of stationary phases in HPLC but it can also be used on other oxides such as alumina, zirconia, titania and thoria. More recent applications have been in the modification of the inner wall of fused silica capillaries for HPCE. The bonded moieties possess high stability and useful applications have been developed for the separation of proteins and peptides under a variety of buffer conditions. The same procedure for modifying the inner wall of a fused silica capillary has also been extended to etched surfaces for use in electrochromatography (CEC). This type of CEC has been shown to be applicable to the sep...

Separation of tetracyclines by high-performance capillary electrophoresis and capillary electrochromatography

Separations of various tetracycline mixtures by high-performance capillary electrophoresis (HPCE) and a new form of electrochromatography (CEC) are compared. The new CEC method involves etching the inner wall of the capillary surface with an appropriate reagent (ammonium dihydrogen fluoride) in order to produce a significant increase in surface area. The etched surface is then modified by a silation/hydrosilation reaction sequence to first produce a hydride intermediate which is then further reacted to attach a C18 moiety. The bare and hydride capillaries are tested under HPCE conditions while the C18 capillary functions in the CEC mode. The effects of pH and the presence of an organic modifier (methanol) are also studied. Detection limits ( < 10 micrograms/ml) are comparable to previous HPLC and HPCE results. Resolutions for mixtures which simulate real analytical problems are equal to or better than those reported for separations on polymeric and diol columns by HPLC and in earlier studies by HPCE and MECC.

Separation of proteins and peptides by capillary electrochromatography in diol- and octadecyl-modified etched capillaries

This study involves the evaluation of a capillary electrochromatography method based on etching the inner walls of a fused-silica tube, which is subsequently modified by a silanization/hydrosilation reaction scheme. Two different organic moieties, octadecyl and diol, are attached to the etched capillary wall. The performance of these two columns is compared to a bare capillary using peptide (angiotensins) and protein samples. It is concluded that the etching process increases the surface area of the inner wall sufficiently to induce solute-bonded phase interactions for the capillaries modified with the octadecyl and diol moieties. The separation capabilities of the two modified capillaries are not the same, presumably due to differences in the chemical properties of the two ligands. When compared to a bare capillary where separation is due only to electrophoretic mobility effects, the bonded etched capillaries also exhibit significant differences in separation factors for the same solutes under identical experimental conditions.

Capillary electrophoretic separation of proteins using stable, hydrophilic poly(acryloylaminoethoxyethanol)-coated columns

Abstract Capillary electrophoretic separations of high efficiency and resolution were obtained using poly(acryloylaminoethoxyethanol)-coated capillaries. The polymer was covalently attached to a silica surface previously modified with a α-methacryloxlypropyl functionality. The latter was realized by catalytic hydrosilylation of allyl methacrylate on an SiH-modified fused-silica capillary. The lifetime of the new type of coating used at pH 8.5 was more than twice that of conventional polyacrylamide.

Open tubular capillary electrokinetic chromatography in etched fused-silica tubes.

This review describes an open tubular approach to capillary electrochromatography (OTCEC) that first etches the inner surface of the fused-silica tube using ammonium hydrogen diflouride. This process can increase the inner surface area significantly. The new surface is then chemically modified to attach a bonded stationary phase using a silanization/hydrosilation reaction process. The surfaces are characterized spectroscopically by diffuse reflectance infrared Fourier transform and by electroosmotic flow measurements. Applications of OTCEC columns with C18, diol and chiral stationary phases are described.

Analysis of hydrophilic metabolites in physiological fluids by HPLC‐MS using a silica hydride‐based stationary phase

Aqueous normal-phase chromatography was used for the analysis of metabolites in human saliva and urine samples. The column was packed with a silica hydride type separation material. Several gradients were tested with different mobile phase additives in order to produce retention for amino acids, small organic acids, and carbohydrates. Detection was done by TOF MS. In some cases the relative concentration levels of various metabolites in human saliva were compared for normal patients and patients with pancreatic cancer or pancreatitis. The reproducibility of retention of individual metabolites in these complex matrices was tested for several compounds.

Molecular shape recognition capability of liquid-crystal bonded phases in reversed-phase high performance liquid chromatography

SummaryThe chromatographic retention behaviour of two liquidcrystal bonded phases have been evaluated using polycyclic aromatic hydrocarbons (PAHs) as the probe samples in reversed-phase high performance liquid chromatography (RP-HPLC). The results clearly indicate that these phases have better planarity and shape recognition capabilities than commercially-avaialble polymeric octadecylsilica (ODS) phases whose strong planarity and shape selectivities were found earlier. It can also be concluded from the chromatographic observations that the shape recognition capability of these phases is dependent on both mobile phase composition and column temperature, but that the effect of mobile phase and temperature on the shape selectivity work independently. The retention behaviour can be explained by changes in the phase structure with changes of eluent composition and temperature.

Open tubular capillary electrochromatography in etched, chemically modified 20 μm I.D. capillaries

Fused silica capillaries with an I.D. of 20 microns are etched and then chemically modified by the silanization/hydrosilation method to attach an octadecyl moiety for use in electrokinetic chromatography. The etched capillaries after chemical modification are shown to have an anodic electroosmotic flow below pH 4.5. In comparison to bare 20 microns capillaries and unetched but chemically modified 20 microns capillaries, the etched C18 fused silica tubes show better separation of mixtures of lysozymes and cytochrome cs under identical conditions of buffer, pH and applied voltage. It was also demonstrated that this open tubular approach to capillary electrochromatography was amenable to a number of different types of basic compounds ranging in size from typical small amines to biomolecules. As expected, pH is an important variable that must be controlled in order to obtain an optimized separation. Reproducibility studies verify the stability of the silicon-carbon linkage produced in this modification method so that column lifetimes of at least 300 injections can be expected.