Sol-gel immobilized cyano-polydimethylsiloxane coating for capillary microextraction of aqueous trace analytes ranging from polycyclic aromatic hydrocarbons to free fatty acids

Sol-gel coating containing highly polar cyanopropyl and nonpolar poly(dimethylsiloxane) components (sol-gel CN-PDMS coating) was developed for capillary microextraction (CME). The sol-gel chemistry provided an efficient means to immobilize the CN-PDMS coating by establishing chemical anchorage between the coating and the fused silica capillary inner surface. This chemical bond provided excellent thermal and solvent stability to the created sol-gel coating. For the extraction of polar and nonpolar analytes, the upper allowable conditioning temperatures were 330 degrees C and 350 degrees C, respectively. To our knowledge, this is the first time when a CN-PDMS thick coating survived such a high operation temperature. The prepared sol-gel CN-PDMS coating provided effective extraction of polar and nonpolar analytes simultaneously from aqueous samples. The cyanopropyl moiety in sol-gel CN-PDMS coatings provided effective extraction of highly polar analytes such as free fatty acids, alcohols, and phenols without requiring derivatization, pH adjustment or salting out procedures. The PDMS moiety, on the other hand, provided efficient extraction of nonpolar analytes. The extraction properties of the sol-gel CN-PDMS coatings can be fine tuned via manipulation of relative proportions of 3-cyanopropyltriethoxysilane and hydroxy-terminated PDMS in the sol solution used to create the coatings. Detection limits of nanogram/liter (ng/L) were achieved for both highly polar and nonpolar analytes directly extracted from aqueous media using sol-gel CN-PDMS coated microextraction capillaries followed by GC analysis.     

Sol-gel methyl coating in capillary microextraction hyphenated on-line with high-performance liquid chromatography Counterintuitive extraction behavior for polar analytes

A sol-gel coating with anchored methyl groups was developed for capillary microextraction hyphenated on-line with high-performance liquid chromatography (HPLC). This was accomplished by using methyltrimethoxysilane as the sol-gel precursor. The methyl group on the sol-gel precursor ultimately turned into a pendant group on the created sol-gel coating and was primarily responsible for the extraction of nonpolar analytes. A 40-cm segment of 0.25mm I.D. fused silica capillary containing the sol-gel methyl coating on the inner surface was installed as a sampling loop in an HPLC injection port. The analytes were extracted by the coating when an aqueous sample containing the analytes was passed through this capillary. The extracted analytes were then transferred to the HPLC column using isocratic elution with an acetonitrile/water mobile phase. This capillary demonstrated excellent extraction capability for polycyclic aromatic hydrocarbons and ketones. Unexpectedly, this coating also provided good extraction for polar analytes, including aromatic phenols, alcohols, and amines. Considering the fact that the methyl group is nonpolar in nature, such an extraction behavior of sol-gel methyl coating toward polar analytes is counterintuitive. Thus, sol-gel sorbents with short alkyl side chains have the potential to offer a polymer-free alternative to traditional sol-gel capillary microextraction (CME) media commonly prepared with the use of polymers in the sol solution. Elimination of polymers from the sol-gel coating solution is conducive to improving thermal stability and solvent tolerance of the created sol-gel extracting phase. This also makes the preparation of sol-gel coatings facile and cost-effective. Possessing excellent solvent stability, such sol-gel coatings offer the opportunity for effective on-line hyphenation of capillary microextraction with HPLC and other liquid-phase separation techniques that employ organo-aqueous mobile phases.     

Solvent-resistant sol-gel polydimethyldiphenylsiloxane coating for on-line hyphenation of capillary microextraction with high-performance liquid chromatography

A sol-gel polydimethyldiphenylsiloxane (PDMDPS) coating was developed for capillary microextraction on-line hyphenated with high-performance liquid chromatography (HPLC). This coating was created using methyltrimethoxysilane (MTMS) as the sol-gel precursor and di-hydroxy-terminated PDMDPS as the sol-gel active polymer. The methyl and phenyl groups on the sol-gel active polymer and the methyl groups on the sol-gel precursor ultimately turned into pendant groups providing the ability to extract non-polar analytes. A 40-cm segment of 0.25mm I.D. fused silica capillary containing the sol-gel PDMDPS coating was installed as an external sampling loop in an HPLC injection port. Aqueous samples containing polycyclic aromatic hydrocarbons (PAHs), aromatic compounds, ketones, and aldehydes were passed through this capillary wherein the analytes were extracted by the sol-gel coating. The extracted analytes were then transferred to the HPLC column using isocratic or gradient elution with an acetonitrile/water mobile phase. This capillary demonstrated excellent extraction capability for non-polar (e.g., polycyclic aromatic hydrocarbons and aromatic compounds) as well as moderately polar compounds, such as aromatic amines, ketones, and aldehydes. The test results indicate that PDMDPS can be successfully immobilized into a sol-gel network and that the resulting solvent-resistant sol-gel organic-inorganic hybrid coating can be effectively used for on-line hyphenation of capillary microextraction with high-performance liquid chromatography. The test results also indicate that the sol-gel PDMDPS coated capillary is resistant to high-temperature solvents, making it suitable for applications in high-temperature HPLC. To the best of our knowledge, this is the first report on the creation of a silica-based sol-gel PDMDPS coating used in capillary microextraction on-line hyphenated to HPLC.     

Parts per quadrillion level ultra-trace determination of polar and nonpolar compounds via solvent-free capillary microextraction on surface-bonded sol-gel polytetrahydrofuran coating and gas chromatography-flame ionization detection

Sol-gel polytetrahydrofuran (poly-THF) coating was developed for high-sensitivity sample preconcentration by capillary microextraction (CME). Parts per quadrillion (ppq) level detection limits were achieved for both polar and nonpolar analytes through sample preconcentration on sol-gel poly-THF coated microextraction capillaries followed by gas chromatography (GC) analysis of the extracted compounds using a flame ionization detector (FID). The sol-gel coating was in situ created on the inner walls of a fused silica capillary using a sol solution containing poly-THF as an organic component, methyltrimethoxysilane (MTMOS) as a sol-gel precursor, trifluoroacetic acid (TFA, 5% water) as a sol-gel catalyst, and hexamethyldisilazane (HMDS) as a deactivating reagent. The sol solution was introduced into a hydrothermally-treated fused silica capillary and the sol-gel reactions were allowed to take place inside the capillary for 60 min. A wall-bonded coating was formed due to the condensation of silanol groups residing on the capillary inner surface with those on the sol-gel network fragments evolving in close vicinity of the capillary walls. Poly-THF is a medium polarity polymer, and was found to be effective in carrying out simultaneous extraction of both polar and nonpolar analytes. Efficient extraction of a wide range of trace analytes from aqueous samples was accomplished using sol-gel poly-THF coated fused silica capillaries for further analysis by GC. The test analytes included polycyclic aromatic hydrocarbons (PAHs), aldehydes, ketones, chlorophenols, and alcohols. To our knowledge, this is the first report on the use of a poly-THF based sol-gel material in analytical microextraction. Sol-gel poly-THF coated CME capillaries showed excellent solvent and thermal stability (>320 degrees C).     

Sol-gel approach to in situ creation of high pH-resistant surface-bonded organic-inorganic hybrid zirconia coating for capillary microextraction (in-tube SPME)

A novel zirconia-based hybrid organic-inorganic sol-gel coating was developed for capillary microextraction (CME) (in-tube SPME). High degree of chemical inertness inherent in zirconia makes it very difficult to covalently bind a suitable organic ligand to its surface. In the present work, this problem was addressed from a sol-gel chemistry point of view. Principles of sol-gel chemistry were employed to chemically bind a hydroxy-terminated silicone polymer (polydimethyldiphenylsiloxane, PDMDPS) to a sol-gel zirconia network in the course of its evolution from a highly reactive alkoxide precursor undergoing controlled hydrolytic polycondensation reactions. A fused silica capillary was filled with a properly designed sol solution to allow for the sol-gel reactions to take place within the capillary for a predetermined period of time (typically 15-30 min). In the course of this process, a layer of the evolving hybrid organic-inorganic sol-gel polymer got chemically anchored to the silanol groups on the capillary inner walls via condensation reaction. At the end of this in-capillary residence time, the unbonded part of the sol solution was expelled from the capillary under helium pressure, leaving behind a chemically bonded sol-gel zirconia-PDMDPS coating on the inner walls. Polycyclic aromatic hydrocarbons, ketones, and aldehydes were efficiently extracted and preconcentrated from dilute aqueous samples using sol-gel zirconia-PDMDPS coated capillaries followed by thermal desorption and GC analysis of the extracted solutes. The newly developed sol-gel hybrid zirconia coatings demonstrated excellent pH stability, and retained the extraction characteristics intact even after continuous rinsing with a 0.1 M NaOH solution for 24 h. To our knowledge, this is the first report on the use of a sol-gel zirconia-based hybrid organic-inorganic coating as an extraction medium in solid phase microextraction (SPME).     

High-performance polyethylene glycol-coated solid-phase microextraction fibers using sol-gel technology

The sol-gel method is applied for the preparation of solid-phase microextraction (SPME) fibers. An electron microscopy experiment suggested a porous structure for Superox-4 (polyethylene glycol, PEG) coating. SPME-GC analyses provided evidence that the sol-gel fibers have some advantages, such as high velocities of mass transfer, efficient extraction rates. high thermal stability, long life span, and spacious range of application for both polar and non-polar analytes. Efficient SPME-GC analyses of benzene-toluene-ethylbenzene-xylenes, phenols, phthalic diesters, naphthalene congeners and pesticides were achieved using sol-gel-coated PEG fibers.     

Applications of Poly(Ethylene)Glycol (PEG) in Separation Science

The wide range of applications of poly(ethylene)glycol (PEG) in primarily chromatography and other closely related analytical methods has been reviewed. PEG has been used as mobile phase modifier in capillary electrophoresis (CE) as well as ion exchange, size exclusion, and hydrophobic interaction liquid chromatography (LC) methods. Generally in the presence of PEG, LC retention of macromolecules is altered and stability of their structure is maintained. PEG was effective in CE as a permanent coating for fused silica capillaries to shield free silanol groups that can cause protein adsorption to the wall resulting in band broadening and low recovery of the separated proteins. In gas chromatography, PEG-based stationary phases were applied for separation of polar analytes. PEG could also serve as an extraction medium in solid phase microextraction and aqueous two phase systems. Selected analytical applications, primarily LC and CE, involving PEG to facilitate the determination of either small molecules or macromolecules such as proteins in their native form are discussed and representative figures provided.

     

Ionic liquid-mediated bis[(3-methyldimethoxysilyl)propyl] polypropylene oxide-based polar sol–gel coatings for capillary microextraction

Two ionic liquids (IL), namely, 1-methyl-3-octylimidazolium chloride (MOIC) and trihexyltetradecylphosphonium tetrafluoroborate (TTPT) were used to prepare polar and nonpolar sol–gel coatings for capillary microextraction (CME). Bis[(3-methyldimethoxysilyl)propyl] polypropylene oxide (BMPO), containing sol–gel active terminal methoxysilyl groups and polar propylene oxide repeating units, was used to prepare polar sol–gel hybrid organic–inorganic coatings. Hydroxy-terminated poly(dimethyl-co-diphenylsiloxane) was used as the sol–gel active organic component for nonpolar sol–gel hybrid coatings. Compared to a sol–gel BMPO coating prepared without IL, the sol–gel BMPO coatings prepared with the use of both of these ILs provided more efficient extraction as is evidenced by more pronounced GC peak areas. The MOIC-mediated sol–gel BMPO coating provided larger GC peak areas compared to the TTPT-mediated sol–gel BMPO coating. Scanning electron microscopy results suggested that MOIC provided a more porous morphology of the sol–gel BMPO extraction media compared to that prepared with TTPT. Thus, individual ILs can affect the porosity of sol–gel materials to different degrees. Overall, the sol–gel BMPO coating prepared with the ILs could extract nonpolar to polar analytes directly from aqueous samples. Detection limits were on the order of nanograms per liter (1.9–330.5 ng/L) depending on the analyte class. Furthermore, the MOIC-mediated sol–gel BMPO coating demonstrated high thermal stability (330 °C), solvent resistance, and fast extraction equilibrium (10–15 min) for polar and moderately polar analytes.     

Development of a Sol-Gel Procedure for Preparation of a Diglycidyloxycalix[4]arene Solid-Phase Microextraction Fiber with Enhanced Extraction Efficiency

5,11,17,23-Tetra-tert-butyl-25,27-dihydroxy-26,28-diglycidyloxycalix[4]arene (diglycidyloxy-C[4]) has been synthesized and used for preparation of a sol-gel solid-phase microextraction fiber with enhanced extraction efficiency. The sol-gel procedure was developed using a sol solution containing diglycidyloxy-C[4] as organic component and both tetraethoxysilane and 3-aminopropyltriethoxysilane (KH-550) as precursors. No additional catalysts were used and no centrifugation was performed. Diglycidyloxy-C[4] was highly chemically reactive toward KH-550 even at room temperature, which increased the calixarene content of the coating, simplified the sol-gel procedure, reduced the sol-gel reaction time, enhanced the polarity of the coating, and improved extraction performance. The sol-gel mixture also had very good coating properties and was highly uniformly distributed on the surface of the fiber; because of these characteristics several fibers could be prepared from one sol-gel solution. Efficient extraction of trace analytes (µg L^?1 levels) from aqueous samples was accomplished using this kind of new fiber. Very low detection limits (ng L^?1 level) were achieved for most polar (aromatic amines and phenols) and nonpolar (polycyclic aromatic hydrocarbons) aromatic compounds by SPME followed by gas chromatography with flame ionization detection. The new coating had excellent solvent and thermal (350 °C) stability. Lifespan was also good—a fiber could be used more than 300 times in headspace SPME without substantial changes in the properties of the coating.     

Preparation and characteristics of high pH-resistant sol-gel alumina-based hybrid organic-inorganic coating for solid-phase microextraction of polar compounds

A novel alumina-based hybrid organic-inorganic sol-gel coating was first developed for solid-phase microextraction (SPME) from a highly reactive alkoxide precursor, aluminum sec-butoxide, and a sol-gel-active organic polymer hydroxyl-terminated polydimethylsiloxane (OH-TSO). The underlying mechanism was discussed and confirmed by IR spectra. The porous surface structure of the sol-gel coating was revealed by scanning electron microscopy. A detailed investigation was conducted to evaluate the remarked performance of the newly developed sol-gel alumina-OH-TSO hybrid materials. In stark contrast to the sol-gel silica-based coating, the alumina-based coating demonstrated excellent pH stability. In addition, good thermal resistance and coating preparation reproducibility are also its outstanding performance. As compared to silica-based hybrids material, the ligand exchange ability of alumina makes it structurally superior extraction sorbents for polar compounds, such as fatty acids, phenols, alcohols, aldehydes and amines. Practical applicability of the prepared alumina-OH-TSO fiber was demonstrated through the analysis of volatile alcohols and fatty acids in beer. The recoveries obtained ranged from 85.7 to 104% and the relative standard deviation values for all analytes were below 9%.     

Sol-gel approach for fabrication of coated anodized titanium wire for solid-phase microextraction: highly efficient adsorbents for enrichment of trace polar analytes

Nanotubular titania film was prepared in situ on titanium wire and was used as the fiber substrate for solid-phase microextraction (SPME) because of its high surface-to-volume ratio, easy preparation, and mechanical stability. Three different functional coatings, β-cyclodextrin (β-CD), β-cyclodextrin-co-poly(ethylenepropylene glycol) (β-CD/PEG), and polyethylene glycol (PEG)-based sorbents were chemically bonded to the nanostructured wire surface via sol-gel technology to further enhance the absorbing capability and extraction selectivity. Coupled to gas chromatography-flame ionic detection (GC-FID), the prepared SPME fibers were investigated using diverse compounds. The results indicated that the fibers showed good mechanical strength, excellent thermal stability, and wonderful capacity and selectivity to polar compounds, including polar aromatic compounds, alcohols, and ketones. Combining the superior hydrophilic property of a bonded functional molecule and the highly porous structure of a fiber coating, the prepared PEG-coated SPME fiber showed much higher adsorption affinity to ephedrine and methylephedrine than β-CD and β-CD/PEG fibers. The as-established PEG-coated SPME-GC analytical method provided excellent sensitivity (LODs, 0.004 and 0.001 ng mL^–1 for ephedrine and methylephedrine, respectively) and better linear range (0.01–2 000 μg L^?1). In addition, it has surprising repeatability and reproducibility. Finally, the present approach was used to analyze ephedrine and methylephedrine from real urine samples, and reliable results were obtained.

A new polyethylene glycol fiber prepared by coating porous zinc electrodeposited onto silver for solid-phase microextraction of styrene

A new polyethylene glycol fiber was developed for solid-phase microextraction (SPME) of styrene by electrodepositing porous Zn film on Ag wire substrate followed by coating with polyethylene glycol sol-gel (Ag/Zn/PEG sol-gel fiber). The scanning electron micrographs of fibers surface revealed a highly porous structure. The extraction property of the developed fiber-to-styrene residue from polystyrene packaged food was investigated by headspace solid-phase microextraction (HS-SPME) and analyzed with a gas chromatograph coupled with flame ionization detection (GC-FID). The new Ag/Zn/PEG sol-gel fiber is simple to prepare, low cost, robust, has high thermal stability and long lifetime, up to 359 extractions. Repeatability of one fiber (n = 6) was in the range of 4.7-7.5% and fiber-to-fiber reproducibility (n = 4) for five concentration values were in the range 3.4-10%. This Ag/Zn/PEG sol-gel fiber was compared to two commercial SPME fibers, 75 μm carboxen/polydimethylsiloxane (CAR/PDMS) and 100 μm polydimethylsiloxane (PDMS). Under their optimum conditions, Ag/Zn/PEG sol-gel fiber showed the highest sensitivity and the lowest detection limit at 0.28 ± 0.01 ng mL⁻¹.     

A novel solid-phase microextraction using coated fiber based sol-gel technique using poly(ethylene glycol) grafted multi-walled carbon nanotubes for determination of benzene, toluene, ethylbenzene and o-xylene in water samples with gas chromatography-flame ionization detector

In this study, poly(ethylene glycol) (PEG) grafted onto multi-walled carbon nanotubes (PEG-g-MWCNTs) were synthesized by the covalent functionalization of MWCNTs with hydroxyl-terminated PEG chains. For the first time, functionalized product of PEG-g-MWCNTs was used as selective stationary phase to prepare the sol-gel solid-phase microextraction (SPME) fiber in combination with gas chromatography-flame ionization detector (GC-FID) for the determination of ultra-trace levels of benzene, toluene, ethylbenzene and o-xylene (BTEX) in real water samples. The PEG-g-MWCNTs were characterized by Fourier transform infrared spectra and also thermo-gravimetric analysis, which verified that PEG chains were grafted onto the surface of the MWCNTs. The scanning electron micrographs of the fiber surface revealed a highly porous structure which greatly increases the surface area for PEG-g-MWCNTs sol-gel coating. This fiber demonstrated many inherent advantages, the main being the strong anchoring of the coating to the fused silica resulting from chemical bonding with the silanol groups on the fused-silica fiber surface. The new PEG-g-MWCNTs sol-gel fiber is simple to prepare, robust, with high thermal stability and long lifetime, up to 200 extractions. Important parameters influencing the extraction efficiency such as desorption temperature and time, extraction temperature, extraction time, stirring speed and salt effect were investigated and optimized. Under the optimal conditions, the method detection limits (S/N=3) were in the range of 0.6-3 pg mL(-1) and the limits of quantification (S/N=10) between 2 and 10 pg mL(-1). The relative standard deviations (RSDs) for one fiber (repeatability) (n=5) were obtained from 4.40 up to 5.75% and between fibers or batch to batch (n=3) (reproducibility) in the range of 4.31-6.55%. The developed method was successfully applied to real water samples while the relative recovery percentages obtained for the spiked water samples at 20 pg mL(-1) were from 90.21 to 101.90%.     

Sol-gel microextraction phases for sample preconcentration in chromatographic analysis

Sol-gel technology provides a simple and reliable method for solid-phase microextraction (SPME) fiber preparation through in situ creation of surface-bonded organic-inorganic hybrid coatings characterized by enhanced thermal stability and solvent-resistance properties that are important for the coupling of SPME with GC and HPLC, respectively. The sol-gel coating technology has led to the development of an extensive array of sol-gel sorbent coatings for SPME. In this article, sol-gel microextraction coatings are reviewed, with particular attention on their synthesis, characterization, and applications in conjunction with GC and HPLC analyses. In addition, the development of sol-gel-coated stir bars, their inherent advantages, and applications are discussed. Next, the development and applications of sol-gel capillary microextraction (CME) in hyphenation with GC and HPLC is extensively reviewed. The newly emerging germania- and titania-based sol-gel microextraction phases look promising, especially in terms of pH and hot solvent stability. Finally, sol-gel monolithic beds for CME are reviewed. Such monolithic beds are in a position to greatly improve the extracting capabilities and enhanced sensitivity in CME.     

溶胶-凝胶法制备用于分离极性有机化合物的毛细管气相柱

 采用溶胶 凝胶法制备了用于分离有机极性化合物的毛细管气相柱 ,其制备工艺简单 ,制柱时间较传统工艺大为缩短。该柱涂层与毛细管内壁间形成的化学键使得其热稳定性好。游离的脂肪酸、有机碱可直接在该柱上得到很好的分离 ,其他极性化合物也在该柱上得到极好的分离。该类柱不仅在同一柱上显示了良好的分离重复性 ,而且不同柱间在容量因子、柱效、对称性及姆氏常数上也显示了良好的重复性。     

Ultra-high-stability,pH-resistant sol–gel titania poly(tetrahydrofuran) coating for capillary microextraction on-line coupled to high-performance liquid chromatography

A sol–gel titania poly(tetrahydrofuran) (poly-THF) coating was developed for capillary microextraction hyphenated on-line with high-performance liquid chromatography (HPLC). Poly-THF was covalently bonded to the sol–gel titania network which, in turn, became chemically anchored to the inner surface of a 0.25 mm I.D. fused silica capillary. For sample preconcentration, a 38-cm segment of the sol–gel titania poly-THF coated capillary was installed on an HPLC injection port as a sampling loop. Aqueous samples containing a variety of analytes were passed through the capillary and, during this process, the analytes were extracted by the sol–gel titania poly-THF coating on the inner surface of the capillary. Using isocratic and gradient elution with acetonitrile/water mobile phases, the extracted analytes were desorbed into the on-line coupled HPLC column for separation and UV detection. The sol–gel titania poly-THF coating was especially efficient in extracting polar analytes, such as underivatized phenols, alcohols, amines, and aromatic carboxylic acids. In addition, this coating was capable of extracting moderately polar and nonpolar analytes, such as ketones and polycyclic aromatic hydrocarbons. The sol–gel titania poly-THF coated capillary was also able to extract polypeptides at pH values near their respective isoelectric points. Extraction of these compounds can be important for environmental and biomedical applications. The observed extraction behavior can be attributed to the polar and nonpolar moieties in the poly-THF structure. This coating was found to be stable under extremely low and high pH conditions—even after 18 h of exposure to 1 M HCl (pH ≈0.0) and 1 M NaOH (pH ≈14.0).     

Solid Phase Microextraction Fibers Coated with Sol-gel Aminopropylsilica/polydimethylsiloxane: Development and Its Application to Screening of Beer Headspace

The preparation and applicability of solid phase microextraction (SPME) fibers coated with a sol-gel organically modified silica based on 3-aminopropyltrimethoxysilane and polydimethylsiloxane (APTMS/PDMS) are described here. Micrographs of the coated fibers revealed a rugous surface; the thickness of the coating was estimated to be less than 30 microm. The APTMS/PDMS fibers were tested with synthetic samples and compared to commercial fibers for headspace SPME analysis of beer. Extraction and desorption using the APTMS/PDMS fibers were faster, which is typical for sol-gel SPME fibers. For polar and semi-polar compounds on beer headspace, the extraction efficiencies of the APTMS/PDMS fiber were superior to those of conventional fibers. The APTMS/PDMS fiber was found to be capable of extracting a broad range of analytes, including highly polar acidic species such as organic acids.     

Negatively charged sol-gel column with stable electroosmotic flow for online preconcentration of zwitterionic biomolecules in capillary electromigration separations

A negatively charged sol-gel coating was developed for on-line preconcentration of zwitterionic biomolecules in capillary electrophoresis (CE), using asparagine and myoglobin as representative zwitterionic bioanalytes. The sol-gel coating was created by using a solution containing three precursors: mercaptopropyltrimethoxysilane (MPTMS), tetramethoxysilane (TMOS), and n-octadecyltriethoxysilane (C18-TEOS). The resulting sol-gel coating contained chemically bonded mercaptopropyl functional groups that were further oxidized by hydrogen peroxide to the corresponding sulfonic acid moieties. Such a surface-bonded sol-gel coating can carry a negative charge over a wide range of pH due to the presence of deprotonated sulfonic acid groups. Under favorable pH conditions, the negatively charged sol-gel coating can facilitate the extraction of positively charged analytes from a zwitterionic sample through electrostatic interaction. This principle was employed to extract myoglobin and asparagine by passing aqueous samples of these zwitterionic analytes through a negatively charged sol-gel column. The extracted analytes were then desorbed and focused via local pH change and stacking. The local pH change was accomplished by passing a buffer solution with a pH above the solute p/ value, while a dynamic pH junction between the sample solution and the background electrolyte was utilized to facilitate solute focusing. The sorption/desorption phenomena could, perhaps, also be explained on the basis of ion-exchange and local pH junction effects. On-line preconcentration and analysis results obtained on sulfonated sol-gel columns were compared with those obtained on an uncoated fused silica capillary of identical dimensions using conventional sample injections. Using UV detection, the presented sample preconcentration technique provided a sensitivity enhancement factor (SEF) on the order of 3 x 10(3) for myoglobin, and 7 x 10(3) for asparagine.     

Modification of micro-cantilever sensors with sol-gels to enhance performance and immobilize chemically selective phases

A chemical sensor based on the deflection of a surface modified silicon micro-cantilever is presented. A thin film of sol-gel was applied to one side of the micro-cantilever surface using a spin coating procedure. The sensor has been shown to give different responses to vapor phase analytes of varying chemical composition, as well as to varying concentrations of a given analyte. Ethanol, a highly polar molecule, exhibits a strong affinity for the polar sol-gel coating resulting in a large response; pentane, a non-polar hydrocarbon, shows very little response. The sol-gel coating has also been shown to function as a backbone for the immobilization of chemically selective phases on the cantilever surface. Reaction of the sol-gel film with chlorotriethoxysilane and subsequent capping of the remaining reactive surface silanols with hexamethyldisilizane increases the non-polar nature of the film. This results in an increase in the response of the sensor to non-polar analytes. The effects of film thickness and cantilever structure thickness on response were also investigated.     

Preparation and investigation of polymethylphenylvinylsiloxane-coated solid-phase microextraction fibers using sol-gel technology

Summary Poly(methylphenylvinylsiloxane) (PMPVS) coating was first prepared using sol-gel technology and applied for solid-phase microextraction (SPME). The extraction properties of the novel coating for volatile and semi-volatile organic compounds were investigated using a homemade SPME device coupled with GC-FID. The porous surface structure of the coating provided high surface area and allowed for high extraction efficiency. Compared with commercial SPME stationary phase, the new phase showed better selectivity and sensitivity toward the various analytes, due to their inherent multifunctional properties and the features of sol-gel chemistry. Furthermore, PMPVS coating showed good thermal stability and long lifetime.