Junior E. Sandoval

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...

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.

Method for the accelerated measurement of electroosmosis in chemically modified tubes for capillary electrophoresis.

A traditional neutral marker approach is combined with fast pressure-driven mobilization to achieve a method that provides accelerated electroosmosis measurements in capillary electrophoresis systems. A marker injection is made prior to and following timed high-voltage application. The marker-sandwiched electrolyte plug is then pressure-driven out of the capillary tube under closely controlled conditions, while the signal is monitored in the usual way. Substantial reduction in measurement time is achieved by allowing the marker to travel only a fraction of the effective length (the injection to detection distance) over a shorter period of time, compared to the traditional method where voltage is applied until the neutral marker shows up at the detector window. One simple equation was derived to express the electroosmotic mobility of the electrolyte (μ(eo)) in terms of common operational variables. The method is particularly useful for low-electroosmosis measurements in wall-modified capillary tubes. The scope and limitations of the method are discussed.

New alumina-based stationary phases for high-performance liquid chromatography: Synthesis by olefin hydrosilation on a silicon hydride-modified alumina intermediate

A silanization procedure is used to form a layer of silicon hydride on the surface of alumina. IR and NMR data confirm the presence of the hydride on the surface. Modification of the hydride intermediate is accomplished by reaction with a terminal olefin in the presence of a transition metal catalyst to form an alkyl-bonded material. Both IR and NMR confirm the bonding of the alkyl ligand to the hydride surface. Chromatographic tests indicate reversed-phase behavior. Exposure to high concentrations of phosphate solution for an extended period resulted in no significant deterioration of the bonded phase.

Chromatographic Evaluation of Alkyl-Bonded Phases Prepared Through Olefin Hydrosilylation on a Hydride-Silica Intermediate.

Abstract The chromatographic characterization of alkyl-bonded silica-based stationary phases for HPLC is described. A previously established method involving catalytic hydrosilylation of terminal olefins on a hydride-modified intermediate was used to obtain octyl and octadecyl packings. Generally speaking, the resulting phases were found to be chromatographically equivalent (comparable retention and selectivity) to sorbents produced in a conventional manner using organosilanization. The new bonded phases are, however, significantly more stable toward hydrolysis than conventional bonded silicas. This highly desirable feature of the new bonded phases not only reduces the need for frequent column replacement but also provides enhanced long-term reproducibility of retention data. The new bonded phases exhibit good separation of polycyclic aromatic hydrocarbons, basic solutes and polypeptides.

CHARACTERIZATION OF WALL MODIFIED SILICA CAPILLARIES FOR OTCEC AND CE

Fused silica capillaries with an i.d. of 50 and 75 μm are chemically modified by the silanization/hydrosilation method to attach organic moieties for use in electrokinetic chromatography. An etching process was utilized to increase the surface area of the capillary inner wall. A comparison of Si-C bonded capillary columns to those obtained by conventional organosilanization (Si-O-Si-C) bond was performed. The etched capillaries after chemical modification are shown to have an anodic electroosmotic flow (EOF) below pH 4.5 while the bare modified capillaries show a cathodic EOF at all pHs studied. The use of these etched chemically modified capillaries eliminates the need for frits and the difficulties associated with packed capillaries such as bubble formation. This open tubular approach to CEC is also suitable for an analysis of a number of different types of basic compounds.