Impregnated Silica Gel Research Articles

Chemotrapping-atomic fluorescence spectrometric method as a field method for volatile arsenic in natural gas

Volatile arsenic compounds in natural gas, existing in the form of trimethylarsine (TMAs), have been determined using gas cryo-trapping gas chromatography coupled to inductively coupled plasma-mass spectrometry (CT-GC-ICP-MS). The results from a number of different gas wells revealed a huge concentration spread ranging from below the detection limit of 0.2 up to 1800 microg/m(3) TMAs (as As) in the gas. Due to the toxicity and corrosive nature of these arsines, they need near real time monitoring via a method that can easily be implemented on site, i.e. during gas exploitation. Here, we introduce a novel method which utilises silver nitrate impregnated silica gel tubes for quantitative chemotrapping of trimethylarsine (TMAs) from a natural gas matrix. Subsequent elution with hot nitric acid followed by online photo-oxidation hydride generation atomic fluorescence spectrometry (HG-AFS) is used for the determination of TMAs gas standards in nitrogen and natural gas samples, respectively. The chemotrapping method was validated using CT-GC-ICP-MS as a reference method. The recovery of arsenic from nitrogen or natural gas matrix ranged from 85 to 113% for a range of 20 to 2000 ng As. Trapping efficiency was >98%, from the methods LOD of 20 ng to 4.8 microg (absolute amount As) with sample sizes of 0.02 and 2 L gas. Method performance was established by comparing the results obtained for eight natural gas samples containing between 1 and 140 microg As/m(3) with those achieved by the reference method (CT-GC-ICP-MS).

Antineoplasic activity of Copaifera multijuga oil and fractions against ascitic and solid Ehrlich tumor

The aim of this study was to investigate the effect of chronic treatment with C. multijuga oil on Ehrlich tumor evolution. C. multijuga was fractionated in a KOH impregnated silica gel column chromatography to give three distinct fractions, i.e., hexanic, chloroformic, and methanolic, mainly composed by hydrocarbon sesquiterpenes, oxygenated sesquiterpenes and acidic diterpenes, respectively. Results demonstrated that the C. multijuga oil, the hexanic, and chloroformic fractions did not develop toxic effects. The oil, hexanic and chloroformic fractions (doses varying between 100 and 200 mg/kg) showed antineoplasic properties against Ehrlich ascitic tumor (EAT) and solid tumor during 10 consecutive days of treatment inhibiting ascitic tumor cell number, reverting medulla and blood cell counts to values similar to control group, and inhibiting the increase on several inflammatory mediators (total protein, PGE 2, nitric oxide, and TNF) on ascitic fluid. The treatment also inhibited the increase in paw volume on tumor-inoculated mice. In conclusion, C. multijuga as well as its fractions demonstrated antineoplasic effect even after oral administration confirming its use by traditional medicine.

Investigation into the determination of trimethylarsine in natural gas and its partitioning into gas and condensate phases using (cryotrapping)/gas chromatography coupled to inductively coupled plasma mass spectrometry and liquid/solid sorption techniques

Speciation of trialkylated arsenic compunds in natural gas, pressurized and stable condensate samples from the same gas well was performed using (Cryotrapping) Gas Chromatography-Inductively Coupled Plasma Mass Spectrometry. The major species in all phases investigated was found to be trimethylarsine with a highest concentration of 17.8 ng/L (As) in the gas phase and 33.2 μg/L (As) in the stable condensate phase. The highest amount of trimethylarsine (121 μg/L (As)) was found in the pressurized condensate, along with trace amounts of non-identified higher alkylated arsines. Volatile arsenic species in natural gas and its related products cause concern with regards to environment, safety, occupational health and gas processing. Therefore, interest lies in a fast and simple field method for the determination of volatile arsenicals. Here, we use simple liquid and solid sorption techniques, namely absorption in silver nitrate solution and adsorption on silver nitrate impregnated silica gel tubes followed by total arsenic determination as a promising tool for field monitoring of volatile arsenicals in natural gas and gas condensates. Preliminary results obtained for the sorption-based methods show that around 70% of the arsenic is determined with these methods in comparison to volatile arsenic determination using GC-ICP-MS. Furthermore, an inter-laboratory- and inter-method comparison was performed using silver nitrate impregnated silica tubes on 14 different gas samples with concentrations varying from below 1 to 1000 μg As/m 3 natural gas. The results obtained from the two laboratories differ in a range of 10 to 60%, but agree within the order of magnitude, which is satisfactory for our purposes.

Separation of Selected Bile Acids by TLC. IX. Separation on Silica Gel 60 and on Silica Gel 60F254 Aluminum Plates Impregnated with Cu(II), Ni(II), Fe(II), and Mn(II) Cations

Seven selected bile acids: cholic acid (C), glycocholic acid (GC), glycolithocholic acid (GLC), deoxycholic acid (DC), chenodeoxycholic acid (CDC), glycodeoxycholic acid (GDC), and lithocholic acid (LC) were separated using adsorption TLC on aluminum plates precoated with silica gel 60 and on aluminum plates precoated with silica gel 60F254. The plates were impregnated with 1%, 2.5%, and 5% aqueous solutions of the following salts: CuSO4, MnSO4, NiSO4, and FeSO4. The mixtures of n–hexane–ethyl–acetate–acetic acid in the volume compositions: 22:20:5 and 25:20:2 (v/v/v) for both aluminum plates, 22:22:5 (v/v/v) only for #1.05554 plates and 25:20:5 (v/v/v) for #1.05553 plates were used as mobile phases. These mobile phases were not effective for the separation of bile acids on non impregnated silica gel 60 and silica 60F254 aluminum plates at 18°C. The plates impregnated with the salts whose application resulted in ΔRF≥0.05 and RS>1 for all neighboring pairs of examined bile acids were considered the most effective for bile acids separation. It was observed that impregnation of silica gel 60 and silica 60F254 aluminum plates with aqueous solutions of CuSO4, MnSO4, NiSO4, and FeSO4 improved the separation of GC/GDC and C/GLC, which separated poorly on aluminum plates precoated with non impregnated silica gel 60 and 60F254. Moreover, it was stated that the use of a mobile phase in volume composition 25:20:2 (v/v/v) and aluminum plates precoated with silica gel 60F254 impregnated with a 5% aqueous solution of CuSO4 made the separation of all neighboring pairs of investigated bile acids possible, in comparison with their separation on non impregnated aluminum plates.

Effects of impregnating variables on dynamic sorption characteristics and storage properties of composite sorbent for solar heat storage

A family of composite sorbents was prepared by impregnating silica gel in the solution of the hygroscopic salt CaCl 2 for solar heat storage. The characteristics of water adsorbed on the composite sorbents prepared under different impregnating conditions were measured by a micromeritics gas adsorption analyzer, a Calvet-type microcalorimeter and an open-type gravimetric method. From the results of these dynamic sorption measurements, the effects of impregnating variables on the characteristics of water adsorbed on the composite sorbents were evaluated. The composite sorbents prepared under different impregnating conditions were also tested on an open-type sorption storage system. The composite sorbent prepared by impregnating in the CaCl 2 solution of 30% showed a high and stable storage capacity of 1020 J g −1 at the charging temperature of about 90 °C. This study demonstrates a great potential in controlling the sorption characteristics as well as the storage properties of the composite sorbents by optimizing the impregnating variables to meet the specific demands of solar heat storage.

Tracing possible structural asymmetry of silica gel used for precoating thin-layer chromatography plates

We have previously described unexpected two-dimensionality in the thin-layer chromatographic separation of pairs of enantiomers of chiral 2-arylpropionic acids (2-APA) by one-dimensional development on a chiral stationary phase prepared by impregnating silica gel layers with l -arginine. The two-dimensionality of this separation was because in planar chromatography all analytes undergo two-dimensional effective diffusion and thus — theoretically at least — can migrate in two mutually perpendicular directions, i.e. in the direction of the mobile phase flow and in a direction perpendicular to this. Demonstration (and quantification) of this striking behavior was possible by use of densitometric detection. Migration of analytes in a direction perpendicular to that of the mobile-phase certainly is not commonplace in thin-layer chromatography and, as far as we are aware, the example described in our previous paper was the first of its kind reported. It was apparently induced by the chirality of the analytes an...

Separation of Selected Bile Acids by TLC. VIII. Separation on Silica Gel 60F254 Glass Plates Impregnated with Cu(II), Ni(II), Fe(II), and Mn(II) Cations

The aim of our study was to examine the following bile acids: cholic acid (C), glycocholic acid (GC), glycolithocholic acid (GLC), deoxycholic acid (DC), chenodeoxycholic acid (CDC), glycodeoxycholic acid (GDC), and lithocholic acid (LC). In the present study, to separate a/m bile acids using adsorption thin layer chromatography at 18°C, the glass plates precoated with silica gel 60F254 (#1.05715), were impregnated with 1%, 2.5%, and 5% aqueous solutions of the following salts: CuSO4, MnSO4, NiSO4, and FeSO4. The mixtures of n‐hexane–ethyl acetate–acetic acid in the volume compositions: 22:20:5; 25:20:2; 25:20:5, and 25:20:8 were used as mobile phases. These mobile phases were not effective for the separation of bile acids on non impregnated silica gel 60F254 plates at 18°C. The plates impregnated with the salts whose application resulted in ΔRF≥0.05 and RS>1 for all neighboring pairs of examined bile acids were considered the most effective for bile acids separation. It was observed that impregnation of silica gel 60F254 glass plates with aqueous solutions of CuSO4, MnSO4, NiSO4, and FeSO4 improved the separation of GC/GDC and C/GLC, which separated poorly on glass plates precoated with non impregnated silica gel 60F254 in adsorption TLC at 18°C.

Thin-layer chromatography of certain metal cations with nonionic surfactant mediated mobile phase systems : separation of co-existing chromium(VI), manganese(II) and iron(III)

Chromatography of eighteen metal cations has been performed on silica gel layers with micellar mobile phases containing nonionic surfactants (Brij-35 and TX-100). The mobility of metal ions was examined under variable experimental conditions of surfactant concentration, mobile phase pH and silica gel layer impregnants (urea and thiourea). The TLC system comprising of aqueous solution of TX-100 (10 - 4 M, pH = 0.8) as mobile phase and 0.1 M thiourea impregnated silica gel layer as stationary phase was identified as the most suitable for the separation of coexisting Cr 6 + , Mn 2 + and Fe 3 + . The interference of several cationic, anionic and molecular impurities on separation of Cr 6 + , Mn 2 + and Fe 3 + was also examined. The lower limit of detection of these metal cations was determined. The proposed method has been used for identification and separation of Cr 6 + , Mn 2 + and Fe 3 + from synthetically prepared alloys.

Lanthanum functionalized highly ordered mesoporous media: implications of arsenate removal

A highly ordered mesoporous silica, SBA-15, was synthesized and various amounts of lanthanum oxide were incorporated into it. Several characterization techniques, such as X-ray diffraction (XRD), nitrogen gas isotherm, and Fourier transform infrared (FTIR) spectroscopy were used to investigate physicochemical properties of the media and to elucidate their arsenate adsorption behavior. The X-ray diffraction and N 2 isotherm results showed that immoderate substitution of lanthanum in the silica network occurred at 80% lanthanum impregnation, even though the lanthanum was highly dispersed inside the mesopore structures of SBA-15 and lanthanum oxide particles did not form on the outside of the solid. As a result of FTIR, however, there was no structural collapse of the silica framework at 80% lanthanum impregnation since partial substitution of lanthanum precursors with silicon occurred; this may play an important role in structural stabilization, as shown by other studies. Although the arsenate adsorption densities increased with an increase in lanthanum impregnation up to 50% (the most efficient percentage of lanthanum impregnation), it abruptly decreased at 80% due to the substitution of lanthanum with silicon, leading to an overall reduction in arsenate adsorption capacity. At the arsenate concentration of 0.667 mmol As/l, the adsorption capacity of 50% lanthanum-impregnated SBA-15 by weight (designated as La 50SBA-15) was 1.651 mmol As/g (123.7 mg As/g), which was approximately 10 and 14 times greater than La(III) impregnated alumina and La(III) impregnated silica gel, respectively.

Photochemical deposition of SERS active silver nanoparticles on silica gel and their application as catalysts for the reduction of aromatic nitro compounds

We report an impregnation technique for immobilization of silver(I) gelatin complex on silica gel. Subsequent UV exposure of the dry impregnated silica gel deposited silver nanoparticles on the solid matrix. Conventional techniques (UV–visible spectroscopy, TEM, EDAX, and thermal analysis) have been used to identify and characterize silver particles on silica surfaces. The photoproduced silver particles have shown unique SERS activity that authenticates the presence of silver nanoclusters in the silica matrix. Hence, the surface of the silica matrix remains SERS-active for months. This surface activity of the silica matrix inspired us to successfully study the catalytic reduction of nitro-compounds in aqueous, organic, and three different micellar media. Different thermodynamic parameters for the reduction processes have also been evaluated. Catalytic activity of the particles in micelles is explained in the light of hydrophobic and electrostatic interactions between the substrate and the micelles.

Epoxidation catalysts

The major component of the cuticular hydroxyfatty acid polymer, cutin, of spinach leaf was identified as 18-hydroxy-cis-9,10-epoxystearic acid. A 3000g particulate fraction obtained from the homogenates of young spinach leaves catalyzed the epoxidation of 18-hydroxyoleic acid to 18-hydroxy-cis-9,10-epoxystearic acid. The epoxy acid was identified by thin-layer chromatography of the product of hydration of the oxirane function and subsequent reduction (octadecane-1,9,10,18-tetraol), on silica gel G and boric acid impregnated silica gel, and by radio gas-liquid chromatography of the periodate oxidation product of the tetraol derived from the epoxy acid. This enzymatic epoxidation required ATP, CoA, NADPH, and O2 for maximal activity. The pH optimum for epoxidation was 9.0, and the epoxidase activity was located mainly in the 3000g particulate fraction, which contained the cuticular membranes. The rate of epoxidation of the unsaturated acid was linear up to 2 h and up to a protein concentration of 1.5 mg/ml. The apparent Km and V of the enzyme was 7.5 × 10−5m and 180 nmol/1-h-mg protein, respectively. That the epoxidase has a stringent substrate specificity was indicated by the observation that 18-hydroxyelaidic acid, 18-acetoxyoleic acid, and oleic acid were not readily epoxidized by this enzyme preparation. Light reversible inhibition by CO suggested the involvement of cytochrome P-450 in the epoxidation. Chelators inhibited epoxidation, and this inhibition was reversed by FeSO4. The epoxidase was inhibited 30% by 0.5 mm NaCN, whereas the same concentration of NaN3 showed very little inhibition. The present epoxidase is unique in that it is associated with the 3000g particles which contain the cutin polymer and in that it requires activation of the carboxyl group distal to the epoxidation site. Enzyme preparations capable of epoxidizing 18-hydroxyoleic acid were also obtained from the skin of apple fruit and from the epidermis of Senecio odoris leaves. This is the first report on an enzyme involved in the biosynthesis of the C18 family of cutin monomer acids.

Synthesis and analysis of symmetrical and nonsymmetrical disaturated/monounsaturated triacylglycerols.

Symmetrical disaturated triacylglycerols of the structure SUS, where S is stearic acid (18:0) and U is an unsaturated fatty acid, either oleic (O; 9cis-18:1), linoleic (L; 9cis,12cis-18:2), or linolenic (Ln; 9cis,12cis,15cis-18:3), are important components providing functionality to interesterified fat blends and structurally modified oils. Nonsymmetrical triacylglycerols of the structure SSU can significantly change melting point and solid fat content profiles. To characterize the physical properties of pure and symmetrical and nonsymmetrical triacylglycerol mixtures, the same reaction sequence has been used to prepare multigram quantities of triacylglycerols SUS and SSU. Tristearin was converted to a mixture of mono-, di-, and triacylglycerols, and the 1,3- and 1,2-diacylglycerol fraction was isolated by silica column chromatography. The 1,3-diacylglycerols were removed by crystallization from acetone and esterified with the appropriate fatty acid to form the symmetrical triacylglycerols with >99% SUS structure. The more difficult to obtain 1,2-diacylglycerols were prepared by esterification of the enriched 1,2-diacylglycerol fraction (80-86% 1,2-diacylglycerols) remaining after removal of much of the 1,3-isomer by crystallization, but silver resin or silver nitrate impregnated silica gel chromatography was required to isolate the nonsymmetrical triacylglycerols. SSL and SSLn were prepared in purities of >98% by this procedure, but not SSO. Silver ion HPLC was found to be as accurate as, and more rapid than, lipolysis/gas chromatography for the determination of the isomeric purities of the synthesized triacylglycerols.

Emission of oxygen, sulphur and nitrogen containing heterocyclic polyaromatic compounds from lignite combustion

Maritza–East Bulgarian lignite was burnt in an atmospheric fluidised bed pilot plant, laboratory scale, at conditions close to the real ones used in power generation (850 °C, 3% oxygen excess, limestone with ratio Ca/S=3.25) in order to analyse in a qualitative way the polycyclic aromatic compounds (PAC) emissions. The samples studied were collected by flowing an aliquot of the combustion gases through a sampling system, consisting of cyclones, nylon and teflon filters and an XAD-2 resin. Before sample analysis by gas chromatography with mass spectrometry detection (GC-MS), ligand exchange chromatography on PdCl 2 impregnated silicagel was used to separate PAC with different heteroatoms, concretely, oxygen (O-PAC), sulphur (S-PAC) and nitrogen (N-PAC) of the polycyclic aromatic hydrocarbon (PAH) fraction. For all samples studied, the highest PAC emissions were due to compounds containing three and four aromatic rings in their structure. The O-PAC constituted carbonyl-containing compounds Z(O)=−18 to −22, with carbon numbers n=13–17; anthraquinones, Z(O 2)=−20, n=14 and 15, phenols, phenanthroaldehyde, and furans, Z(O)=−22, n=16, where concentration of quinones far predominated. A peculiar group of C 19–C 23 alkylbenzones, with a maximum at C 20–C 21, was found as well. Dibenzothiophenes, phenanthrothiophene and benzonaphthothiophenes, Z(S)=−16 to −20, were the major constituents of the S-PAC, while the N-PAC were determined at trace levels.

Variability of fatty acid components of marine and freshwater gastropod species from the littoral zone of the Red Sea, Mediterranean Sea, and Sea of Galilee

Eight marine gastropod species from the littoral zone of the Red and Mediterranean Seas, and four freshwater gastropods from the Sea of Galilee were analysed for their fatty acid composition using TLC (silver nitrate impregnated silica gel) and gas chromatography–mass spectrometry (GC/MS). The major fatty acid components in all twelve samples were polyunsaturated fatty acids (PUFA). The total lipids of the Sea of Galilee species contained considerably more 22:6n-3 (from 10.33% to 12.63%) and 20:5n-3 (up to 2.67%) than those from marine species. The differences among the PUFA in these species appear to be due mainly to different environmental conditions, dietary habits and geographical spreading.

Determining dioxin-like compounds in selected Korean food

To measure the levels of dioxin-like compounds, pork, mackerel, cheese and milk were analyzed. The food samples were obtained at three different markets in Seoul. All the samples were animal origin and their lipid contents ranged from 4% to 34%. After extraction, extracts were cleaned up by sulfuric acid impregnated silica gel, purified on a series of silica gel, alumina, carbon column chromatography and then analyzed by high resolution gas chromatography/high resolution mass spectrometry. The levels of polychlorinated dibenzo- p-dioxins/furans for pork, mackerel, cheese and milk were 0.0008, 0.8663, 0.002 and 0.0236 pgTEQ/g wet weight, respectively. In addition, the levels of non-ortho coplanar polychlorinated biphenyls for pork, mackerel, cheese and milk were 0.0041, 1.5781, 0.0259 and 0.0353 pgTEQ/g wet weight, respectively. Among food samples analyzed, pork showed the lowest level of dioxin-like compounds.

Alkadienes and alkenes, sex pheromone components of the almond seed wasp Eurytoma amygdali.

Whole body extracts of virgin Eurytoma amygdali females were attractive to males in laboratory bioassays. Extracts of various body parts of the female wasp elicited different responses to males, with the thorax extract being the most active. Preparative fractionation of the crude hydrocarbon extract on a silver nitrate impregnated silica gel column (alkanes, alkenes, and alkadienes) revealed that the highest male response was elicited by alkadienes and the lowest by alkenes, with the alkane fraction being inactive. The identification of alkenes and alkadienes was based on gas chromatographic, mass spectrometric, and gas-phase infrared data. Laboratory bioassays suggested that the two alkadienes, (Z,Z)-6,9-tricosadiene [(Z,Z)-6,9-C23:2], and (Z,Z)-6,9-pentacosadiene [(Z,Z)-6,9-C25:2], and to a lesser extent alkenes, identified in the female extract of E. amygdali were male attractants.

Phenolic constituents from the lichen Parmotrema stuppeum (Nyl.) Hale and their antioxidant activity.

Lichen, Parmotrema stuppeum (P. stuppeum) was successively extracted with benzene and acetone. Both the extracts were fractionated on 1% oxalic acid impregnated silica gel column to obtain four phenolic compounds. The structures of compounds were identified by 1H and 13C NMR spectra as methyl orsenillate, orsenillic acid, atranorin and lecanoric acid respectively. Antioxidant activity of benzene extract, acetone extract and isolated compounds were evaluated in a beta-carotene-linoleate model system. The pure compounds showed moderate antioxidant activity. This is the first report on the isolation and characterisation of compounds from the lichen P. stuppeum as well as on their antioxidant activity.

Separation of acid diterpenes of Copaifera cearensis huber ex ducke by flash chromatography using potassium hydroxide impregnated silica gel

Various acid diterpenes of Copaifera cearensis Huber ex Ducke were isolated from the crude extract by flash Silica Gel/Potassium Hydroxide Chromatography. The main components were identified by GC-MS analyses. Further fractionation by reversed phase (RP) semi-preparative HPLC allowed isolation and identification of minor components and provided additional spectral data of those compounds. It was possible to detect the presence of eleven acid diterpenes in addition to a sesquiterpene acid. In addition to potassium hydroxide deposition on the silica surface, the presence of Si-OK residues, resulting from a cation exchange process, was established.

SEPARATION OF STEROLS AND TRITERPENE ALCOHOLS FROM UNSAPONIFIABLE FRACTIONS OF THREE PLANT SEED OILS

Preparative HPLC was used to separate sterols and triterpene alcohols from the unsaponifiable matters in plant oils from Camellia weiningensis L., Brassica juncea L. and Microula sikkimensis. The isolated sterols and triterpene alcohols were acetylated and further purified by AgNO3 impregnated silica gel preparative thin layer chromatography (TLC). The isolated acetyl derivatives of sterols and triterpene alcohols were identified by melting point, specific rotation, infrared and mass spectrometry. The sterols were brassicasterol, campesterol, stigmasterol, β-sitosterol and Θ5-avenasterol, Θ7-avenasterol, Θ7-stigmastenol and α-spinasterol. The triterpene alcohols were cycloartanol, cycloartenol, 24-methylenecycloartanol, cyclobranol, dammaradienol, tirucalla-7,24-dienol, butyrospermol, β-amyrin, germanicol, α-4-taraxasterol and lupeol.

Main Aroma Constituents of Genipap (Genipa americana L.) and Bacuri (Platonia insignis M.)

Volatile compounds of the fruits genipap (Genipa americana L.) and bacuri (Platonia insignis Mart.) were investigated by GC/MS. GC-olfactometry by AEDA pointed the main aroma impact compounds in both fruit extracts, mainly linalool and methyl hexanoate in bacuri. In genipap, high amounts of carboxylic acids were detected after a KOH impregnated silica gel open column chromatography, used to separate the carboxylic acids from the neutral compounds presented. GCO/AEDA pointed to butyric, 2-methylbutyric and hexanoic acids as the impact aroma compounds responsible for the acidic and pungent notes observed in genipap. Beside these, the ethyl esters of 2- and 3-methylbutyric acids were also pointed as the most intense and characteristic fruity notes in that fruit.