Monolithic Silica Gel Research Articles

Profiling volatile compounds from culture supernatants of periodontal bacteria using gas chromatography/mass spectrometry/olfactometry analysis with a monolithic silica gel adsorption device

Halitosis is formed mainly by the volatile compounds produced by periodontal bacteria. Three volatile sulfur compounds (VSCs), hydrogen sulfide, methanethiol, and dimethyl sulfide, have attracted attention as major components of halitosis. However, these compounds cannot account for all odors. In this study, we profiled volatile compounds from the culture supernatants of periodontal bacteria using gas chromatography/mass spectrometry/olfactometry analysis with a monolithic silica gel adsorption device to investigate the potential odorous compounds. Periodontal bacteria have been found to produce volatile compounds belonging to various classes, such as alcohols, ketones, fatty acids, and aromatic compounds, in addition to VSCs. In addition, VSCs different from hydrogen sulfide and methanethiol, which are considered important causative compounds, may also influence to halitosis.

Nonlinear optical responses of carbon quantum dots anchored on graphene oxide hybrid in solid-state transparent monolithic silica gel glasses

Exploring the nonlinear optical (NLO) response of graphene-based hybrids in solid-state three-dimensional macrostructures is vital to promote the practical development of graphene-based photonic and optoelectronic devices. Here, a solid-state hybrid of ultrafine and well-dispersed carbon quantum dots (CQDs) supported on graphene oxide (GO) was chosen as representative of such materials. The hybrid was introduced into organically modified silica gel glasses using a facile sol-gel wet chemical technique to obtain stable transparent monolithic nanocomposites, and their practical application in nonlinear optics was explored. The NLO performances were investigated by the open-aperture (OA) and closed-aperture (CA) Z-scan techniques in the nanosecond regime using a laser with a wavelength of 532 nm. The as-prepared CQD/GO SiO2 gel glasses displayed completely different NLO behavior from that of a CQD/GO suspension. The NLO performance of CQD/GO significantly improved after incorporation into SiO2 gel glasses because of the more graphitized structure of the CQD/GO hybrid. Both the OA and CA Z-scan patterns suggested that the NLO properties of the CQD/GO suspension combined nonlinear absorption and nonlinear scattering, while the NLO response of the CQD/GO SiO2 gel glasses stemmed primarily from nonlinear absorption and nonlinear refraction. In addition, this is the first report of the third-order nonlinear susceptibility χ(3) of a CQD/GO hybrid doped in solid-state gel glasses. The present results therefore demonstrate the feasibility and versatility of CQD/GO silica gel glasses, a promising new class of highly efficient NLO materials that can be applied in optical communications, radiofrequency optoelectronics, and all-optical signal processing.

Monolithic silica columns with covalently attached octaproline chiral selector. Dependence of performance on derivatization degree and comparison with a bead-based analogue

A monolithic silica gel chromatographic matrix was derivatized repetitively with an octaproline-derived chiral selector (CS). The increasingly derivatized column was tested after each derivatization reaction. The enantioseparation ability, resolution and efficiency were found to depend on the content of CS attained after each reaction. Moreover, enantioselectivity and performance of the column with the highest CS coverage were compared to those of a bead-based chiral stationary phase (CSP) counterpart. The octaproline-derivatized monolithic column demonstrated increased enantioseparation factors, resolution and broader applicability than the particle-based column. Finally, the loading capacity of the CSPs was also examined. The monolithic octaproline-derived column permits the separation of 3–20 times higher molar amounts of the tested analytes (depending on the compound considered) than the particle-based counterpart. The enhanced capabilities of the derivatized monolithic column with respect to that of a bead-based counterpart cannot be explained only on the basis of an increased CS coverage. The involvement of an effect produced by the chromatographic silica support structure in the obtained results is discussed.

Monolithic silica columns functionalized with substituted polyproline-derived chiral selectors as chiral stationary phases for high-performance liquid chromatography.

In this study, two polyproline-derived chiral selectors are bonded to monolithic silica gel columns. In spite of high chiral selector coverage, the derivatization was found to have only a slight effect on the hydrodynamics of the mobile phase through the column. The enantioseparation ability of the resulting chiral monolithic columns was evaluated with a series of structurally diverse racemic test compounds. When compared to analogous bead-based chiral stationary phases, higher enantioseparation and broader application domain were observed for monolithic columns. Moreover, the increase in flow rate produces a minor reduction of resolution, which permits to shorten analysis time. Additionally, increased loadability defines chiral polyproline derived monoliths as adequate for preparative chromatography.

Rapid reversed-phase liquid chromatography separation of cyclolinopeptides with monolithic and microparticulate columns

Three monolithic C18-bonded silica gel columns i.e. Chromolith® SpeedROD (CSR), Chromolith® Performance (CP), and Chromolith® High Resolution (CHR), MerckKGaA Darmstadt, Germany and two particle-based columns i.e. ZORBAX Eclipse XDB-C18 (ZEX), Agilent and POROS R1/20 (POR), Applied Biosystems were compared for their performance in separating a mixture of flaxseed cyclolinopeptides (CLs). Gradient mobile phases of acetonitrile and water were optimized for each column. The performance of CHR column in profiling CL standards, measured as the resolution of individual CL, selectivity, and peak asymmetry exceeded the performance of traditional particle-packed columns and the other monolithic columns. The profiling of CLs in aqueous methanolic flaxseed extract was optimized for high-throughput analysis. A total analysis time of 1.5min at a flow rate of 3.0mLmin−1 was achieved on a CSR column. Injection of over 2000 methanol extracts of flaxseed on a CSR column had no impact on backpressure or resolution of a standard CL mixture.

A new method for quantitative determination of dimemorfan in human plasma using monolithic silica solid-phase extraction tips

Dimemorfan was extracted from human plasma samples (100 μL) using MonoTip C(18) tips, which were packed with a C(18)-bonded monolithic silica gel attached to the inside of the tip. The samples, which contained dimemorfan and trimeprazine as an internal standard (IS), were mixed with 300 μL of distilled water and 50 μL of 1M glycine-sodium hydroxide buffer (pH 10). The mixture was extracted onto the C(18) phase of the tip by 20 sequential aspirating/dispensing cycles using a manual micropipettor. The analytes retained on the C(18) phase were then eluted with methanol by five sequential aspirating/dispensing cycles. The eluate was injected directly into a gas chromatograph and detected by a mass spectrometer with selected ion monitoring in positive electron ionization mode. An Equity-5 fused silica capillary column (30 m × 0.32 mm i.d., film thickness 0.25 μm) gave adequate separation of the dimemorfan, IS, and impurities. The recoveries of dimemorfan and the IS spiked into plasma were ≥83%. The regression equation for dimemorfan showed excellent linearity from 0.25 to 32.0 ng/100 μL of plasma, and the limit of detection was 0.125 ng/100 μL of plasma. The maximum intra-day and inter-day relative standard deviations were 13%, while accuracy ranged from 88% to 105%. Dimemorfan was stable for at least 12 h at 4°C, 4 weeks at -80°C, and three freeze-thaw cycles in plasma. This new method is expected to have application as a pretreatment for the rapid, simple, and quantitative determination of dimemorfan in plasma samples.

A simple and reliable method for quantifying plasma concentrations of tetracyclic antidepressants using monolithic silica solid-phase extraction tips

Three tetracyclic antidepressants, mianserin, mirtazapine, and setiptiline, were extracted from human plasma samples using a new micropipette solid-phase extraction tip containing a monolithic silica gel packing material, the MonoTip C18. The plasma samples (0.1 ml), which contained mianserin, mirtazapine, and setiptiline, were mixed with 330 μl of distilled water and 50 μl of 0.5 M glycine–sodium hydroxide buffer solution (pH 8). After centrifugation, the supernatant was extracted onto the C18 phase of the tip (pipette tip volume, 200 μl) by 25 sequential aspirating/dispensing cycles. The three analytes retained in the C18 phase were eluted with methanol by 5 aspirating/dispensing cycles. The eluate was subjected to measurements by gas chromatography (GC) with nitrogen–phosphorus detection (NPD). The recoveries of the three antidepressants were 84.6–99.6% and the limits of detection for each drug were between 2.4 and 15 ng/ml of plasma. The maximum intraday and interday coefficients of variation for the drugs was below 10.6%. Regression equations for the three drugs showed excellent linearity in the range of 50–5000 ng/ml for mianserin and mirtazapine and 50–10 000 ng/ml for setiptiline. The antidepressants were stable for at least 12 h at 4°C, 4 weeks at −80°C, and through three freeze–thaw cycles in plasma. The validated method was successfully used to quantify the plasma concentrations of mirtazapine in a human subject after oral administration of the drug. Although we achieved analyte detection with GC-NPD, the present monolithic micropipette extraction method for tetracyclic antidepressants seems to be very useful for combining it with GC–mass spectrometry (MS) and/or liquid chromatography–tandem MS to secure high simplicity, purification, reproducibility, and sensitivity.

Determination of dextromethorphan in human plasma using pipette tip solid-phase extraction and gas chromatography–mass spectrometry

Dextromethorphan was extracted from human plasma samples (100 μL) using MonoTip C(18) tips, which are packed with C(18)-bonded monolithic silica gel that is attached to the inside of the tip. The samples, which contained dextromethorphan and trimeprazine as an internal standard (IS), were mixed with 200 μL of distilled water and 50 μL of 1 mol/L glycine-sodium hydroxide buffer (pH 10). The mixture was extracted to the C(18) phase of the tip by 20 sequential aspirating/dispensing cycles using a manual micropipettor. The analytes retained on the C(18) phase were then eluted with methanol by five sequential aspirating/dispensing cycles. The eluate was injected directly into a gas chromatograph and detected by a mass spectrometer with selected ion monitoring in positive electron ionization mode. An Equity-5 fused silica capillary column (30 m × 0.32 mm i.d., film thickness 0.5 μm) gave adequate separation of the dextromethorphan, IS, and impurities. The recoveries of dextromethorphan and the IS spiked into plasma were >87.4%. The regression equation for dextromethorphan showed excellent linearity from 2.5 to 320 ng/mL of plasma, and the limit of detection was 1.25 ng/mL of plasma. The intraday and interday coefficients of variation were less than 10.5% and 14.7%, respectively. The accuracy ranged from 91.9% to 107%. The validated method was successfully used to quantify the plasma concentration of dextromethorphan in a human subject after oral administration of the drug.

Glucose sensing by time-resolved fluorescence of sol-gel immobilized glucose oxidase.

A monolithic silica gel matrix with entrapped glucose oxidase (GOD) was constructed as a bioactive element in an optical biosensor for glucose determination. Intrinsic fluorescence of free and immobilised GOD was investigated in the visible range in presence of different glucose concentrations by time-resolved spectroscopy with time-correlated single-photon counting detector. A three-exponential model was used for analysing the fluorescence transients. Fractional intensities and mean lifetime were shown to be sensitive to the enzymatic reaction and were used for obtaining calibration curve for glucose concentration determination. The sensing system proposed achieved high resolution (up to 0.17 mM) glucose determination with a detection range from 0.4 mM to 5 mM.

Free-Form, High Energy Performance, Transparent Envelope

This article examines, from the energy viewpoint, a new lightweight, slim, high energy efficient, light-transmitting envelope system, providing for seamless, free-form designs for use in architectural projects. The research was based on envelope components already existing on the market, especially components implemented with granular silica gel insulation, as this is the most effective translucent thermal insulation there is today. The tests run on these materials revealed that there is not one that has all the features required of the new envelope model, although some do have properties that could be exploited to generate this envelope, namely, the vacuum chamber of vacuum insulated panels (VIP), the monolithic aerogel used as insulation in some prototypes, reinforced polyester barriers. By combining these three design components — the high-performance thermal insulation of the vacuum chamber combined with monolithic silica gel insulation, the free-form design potential provided by materials like reinforced polyester and epoxy resins—, we have been able to define and test a new, variable geometry, energy-saving envelope system.

UTLC of flavonols inSambucus nigraflowers

UTLC is a new, miniaturized form of thin-layer chromatography. In comparison with classical TLC or HPTLC it enables analysis of substantially smaller amounts of compounds. Monolithic silica gel layers have been used for separation of amino acids, alkaloids, steroids, and phenols [1–4]. There are no literature reports of the application of UTLC for analysis of compounds present in matrices originating from plants. Miniaturization of the chromatographic process enables the analysis of much smaller samples of plant material; this is especially important for screening of a large group of plants. The flowers of black elder – Sambucus nigra L. (Caprifoliaceae) have been used in folk medicine for centuries as a diuretic and diaphoretic remedy [5, 6]. Nowadays, this medicinal plant is a constituent of many phytopharmaceuticals used for treatment of influenza, colds, and sinusitis. Flavonols, including rutin, quercetin, quercetin 3-O-glucoside are believed to be responsible for the therapeutic effects of elderberry flowers [6]. This work was an attempt to apply UTLC to analysis of the flavonoids occurring in plant matrices. The objective of the research was to optimize the conditions for UTLC separation of flavonols present in the flowers of Sambucus nigra.

Fiber-optic glucose biosensor based on glucose oxidase immobilised in a silica gel matrix

A monolithic silica gel matrix with entrapped glucose oxidase was constructed as a bioactive element in an optical biosensor for glucose determination. Physicochemical and biochemical characterizations of the catalytic matrix were performed, and the intrinsic fluorescence of immobilised glucose oxidase (GOD) was investigated in the UV and visible range by performing steady state and time course measurements. In all cases, the silica gel matrix proved to be a suitable support for optical biosensing owing to its superior optical properties (e.g., high transmittance and reliable fluorescence and GOD absorption spectra after immobilisation). From steady state measurements, calibration curves were obtained as a function of glucose concentration. When time course measurements were performed, the silica gel support displayed a larger linear calibration range and higher sensitivity than other immobilisation systems. In addition, a glucose optical biosensor was developed and characterised using as catalytic element GOD immobilised on a gel disk bound to a bundle of optical fibres.

Multiscale Templating of Siloxane Gels via Polymerization-Induced Phase Separation

By combining the micellar templating in nanometer-scale with the polymerization-induced phase separation in micrometer-scale, we can synthesize monolithic silica or silsesquioxane gel materials with hierarchical well-defined macropores and shape-controlled mesopores. Depending on the mechanism of enhancing micellar-templating of siloxane oligomers, macroframeworks containing long-range-ordered cylindrical mesopores with different degrees of order have been produced. Alkylene-bridged silicon alkoxides can also be prepared into similarly hierarchical porous structures with broadened variations in framework morphology. These examples demonstrate the versatility of using phase-separation in micellar-templated gelling systems to obtain well-defined macroporous structures.

Comparative TOF‐SIMS and MALDI TOF‐MS analysis on different chromatographic planar substrates

A comparison is made between two high resolution, surface-based, mass spectrometric methods: time-of-flight secondary ion mass spectrometry (TOF-SIMS) and matrix-assisted laser desorption/ionisation mass spectrometry (MALDI TOF-MS) in indication of abietic and gibberellic acids molecular profiles on different chromatographic thin layers. The analytes were applied to silica gel chromatographic thin layers with SIMS on-line interfacing channel, monolithic silica gel ultra-thin layers, and thin layers specifically designed for direct Raman spectroscopic analysis. Two MALDI matrices were used in this research: ferulic acid and 2,5-dihydroxybenzoic acid. The silica gel SIMS-interfacing channel strongly supported formation of numerous different MALDI MS fragments with abietic and gibberellic acids, and ferulic acid matrix. The most intense fragments belonged to [M-OH](+) and [M](+) ions from ferulic acid. Intense conjugates were detected with gibberellic acid. The MALDI MS spectrum from the monolithic silica gel surface showed very low analyte signal intensity and it was not possible to obtain MALDI spectra from a Raman spectroscopy treated chromatographic layer. The MALDI TOF MS gibberellic acid fragmentation profile was shielded by the matrix used and was accompanied by poor analyte identification. The most useful TOF-SIMS analytical signal response was obtained from analytes separated on monolithic silica gel and a SIMS-interfacing modified silica gel surface. New horizons with nanostructured surfaces call for high resolution MS methods (which cannot readily be miniaturised like many optical and electrochemical methods) to be integrated in chip and nanoscale detection systems.

Pipette tip solid-phase extraction and gas chromatography – mass spectrometry for the determination of methamphetamine and amphetamine in human whole blood

Methamphetamine and amphetamine were extracted from human whole blood samples using pipette tip solid-phase extraction (SPE) with MonoTip C(18) tips, on which C(18)-bonded monolithic silica gel was fixed. Human whole blood (0.1 mL) containing methamphetamine and amphetamine, with N-methylbenzylamine as an internal standard, was mixed with 0.4 mL of distilled water and 50 microL of 5 M sodium hydroxide solution. After centrifugation, the supernatant was extracted to the C(18) phase of the tip (pipette tip volume, 200 microL) by 25 repeated aspirating/dispensing cycles using a manual micropipettor. Analytes retained in the C(18) phase were eluted with methanol by five repeated aspirating/dispensing cycles. After derivatization with trifluoroacetic anhydride, analytes were measured by gas chromatography - mass spectrometry with selected ion monitoring in the positive-ion electron impact mode. Recoveries of methamphetamine and amphetamine spiked into whole blood were more than 87.6 and 81.7%, respectively. Regression equations for methamphetamine and amphetamine showed excellent linearity in the range of 0.5-100 ng/0.1 mL. The limits of detection for methamphetamine and amphetamine were 0.15 and 0.11 ng/0.1 mL, respectively. Intra- and interday coefficients of variation for both stimulants were not greater than 9.6 and 13.8%, respectively. The determination of methamphetamine and amphetamine in autopsy whole blood samples is presented, and was shown to validate the present methodology.

Simultaneous determination of methamphetamine and amphetamine in human urine using pipette tip solid-phase extraction and gas chromatography–mass spectrometry

Methamphetamine and amphetamine were extracted from human urine samples using pipette tip solid-phase extraction (SPE) with MonoTip C 18 tips (pipette tip volume, 200 μl), in which C 18-bonded monolithic silica gel was fixed. A sample of human urine (0.5 ml) containing methamphetamine, amphetamine, and N-methylbenzylamine as internal standard (IS), was mixed with 25 μl of 1 M sodium hydroxide solution. The mixture was extracted into the C 18 phase of the SPE tip by 25 repeated aspirating/dispensing cycles using a manual micropipettor. Analytes retained in the C 18 phase were then eluted with methanol by five repeated aspirating/dispensing cycles. After derivatization with trifluoroacetic anhydride, analytes were measured by gas chromatography/mass spectrometry with selected ion monitoring in the positive-ion electron impact mode. Recoveries of methamphetamine, amphetamine, and IS spiked into urine were more than 82.9, 82.2, and 78.2%, respectively. Regression equations for methamphetamine and amphetamine showed excellent linearity in the range of 0.25–200 ng/0.5 ml. Limit of detection was 0.04 ng/0.5 ml for methamphetamine and 0.05 ng/0.5 ml for amphetamine. Intra- and inter-day coefficients of variations for both stimulants were not greater than 10.8%. The data obtained from actual determination of methamphetamine and amphetamine in autopsy urine samples are also presented for validation of the method.

Separation of Polyprenols Using a Monolithic Silica Column in High-Performance Liquid Chromatography

The use of monolithic silica gel columns for the analysis of natural polyprenols have been described. Separation of natural polyprenols by high-performance liquid chromatography (HPLC) using the Chromolith Performance octadecylsilyl (ODS) monolithic silica column (Merck) was compared with that using a conventional microparticulate ODS-bonded silica column. A system comprising two connected monolithic columns afforded an equivalent separation at half the analysis time of the conventional method. Furthermore, ten connected columns achieved a tremendously high-resolution separation; complicated series of homologous polyprenols having geometric isomers were separated completely. Additionally, we attempted the analysis of naturally occurring polyprenols and dolichols using a monolithic silica capillary column for HPLC. First, separation of the polyprenol mixture alone was performed using a 250 × 0.2 mm i.d. ODS-monolith silica capillary column. The separation resolution (RS) between octadecaprenol (prenol 18) and nonadecaprenol (prenol 19) was two time or more higher than that recorded when a conventional ODS-silica particle-packed column (250 × 4.6 mm i.d.) was used under identical elution conditions. Next, a mixture of the prenol type (polyprenol) and dolichol type (dihydropolyprenol) was subjected to analysis using this capillary HPLC system, and each homologue was separated successfully. During analysis of the polyprenol fraction derived from Eucommia ulmoides leaves, in addition to the all-trans-polyprenol and cis-polyprenol that were previously identified, dolichols were observed as a single peak. This high-resolution and sensitive system is very useful for the analysis of compounds that are structurally similar to polyprenols and dolichols and have small amounts of these alcohols.

Novel Method for DNA Isolation Using High-throughput Monolithic Silica Gel Column in Combination with Anti-chaotropic Effect

Abstract DNA molecules were completely adsorbed by the silica gel in the presence of saturated ammonium sulfate with a marked anti-chaotropic property, and the adsorbed DNAs were quantitatively desorbed with a low salt buffer. Based on such adsorption–desorption behavior of DNA, a novel isolation method for DNA was successfully developed.

High-throughput protein digestion by trypsin-immobilized monolithic silica with pipette-tip formula

Based on the monolithic silica gel materials with hierarchical pore structure and on the SPE devices (MonoTip®) developed thereof, a trypsin-immobilized monolithic silica in a pipette tip (MonoTip® Trypsin) suitable for digesting proteins has been newly developed. The surface of monolithic silica fixed into the tip was chemically modified with trypsin via an aminopropyl group. Trypsin-immobilized monolith successfully performed a rapid digestion of reduced and alkylated proteins with only a few times pipetting operation for the pre-treatment procedure of chromatographic analysis. The novel solid-phase digestion tool using monolithic silica allows a high-throughput trypsin proteolysis of bio-substances in proteomics.

ToF-SIMS characterisation of diterpenoic acids after chromatographic separation

Microcolumn liquid chromatography (μHPLC) coupled on-line with time of flight secondary ion mass spectrometry (ToF-SIMS) was applied for mixture of diterpenoic acids (abietic, gibberellic and kaurenoic) analysis. Chromatographic effluent, with analytes separated, was carried out directly onto different, ToF-SIMS compatible surface substrates, for further ToF-SIMS analysis. Silica gel Si 60, aluminium backplate modified Si 60, monolithic silica gel and Raman spectroscopy chromatographic thin layers were used as the deposition substrates in this experiment. By ToF-SIMS surface imaging the deposition trace picture has been obtained. Effluent deposition surface area was scanned for diterpenoic acid fragment mass values based on mass spectrometric library. Measured ToF-SIMS dataset of fragment abundance and intensities were used for preliminary fragmentation schemes construction. The lowest substrate background activity has been established for monolithic silica gel thin layer and aluminium backplate modified Si 60 thin layer. In the case of Raman spectroscopy pre-treated thin layer or conventional chromatographic thin layer Si 60, the both, high background signal intensity and impossibility to construct negative ions surface image, were observed. Diterpenoic acids studied serve the similar mass spectrum but ToF-SIMS coupled with liquid chromatographic separation brings new impact to the positive identification of analytes studied.