Search results for "silica"
showing 10 items of 1092 documents
Modelling of the cation motions in complex system: case of Na-mordenites
2002
Abstract Semi-empirical inter-atomic potentials and Monte Carlo algorithms are proposed to predict the evolution of the interaction energy between sodium ions and a mordenite type aluminosilicate network as a function of Si/Al ratio. This result is favourably compared with the activation energy barriers for Na + `jumps' responsible for the polarization change, measured by thermally stimulated current (TSC) spectroscopy, for Na-mordenites characterized by Si/Al ratios ranged from 5.5 to 12. Finally, we propose a possible mechanism for the cation motions, which involves activation barriers within the same order of magnitude than those measured by TSC.
ChemInform Abstract: Modular Metal Chalcogenide Chemistry: Secondary Building Blocks as a Basis of the Silicate-Type Framework Structure of CsLiU(PS4…
2012
The new title compound is synthesized from a mixture of U, P2S5, Li2S, Cs2S, and S in the molar ratio 2:2:1:1:4 (sealed silica tube, 700 °C, 3 d).
Effect of the Al/Si atomic ratio on surface and structural properties of sol-gel prepared aluminosilicates
2003
Abstract A series of aluminosilicates with an Al/Si ratio ranging from 0 to ∞ (0 for pure silica and ∞ for pure alumina) was prepared by sol–gel process and characterized by surface and structure techniques. Aluminum tri sec butoxide and tetramethylorthosilicate were used as precursors for the sol–gel synthesis. The acidic properties of the oxides were studied by determination of the zero point charges, through mass titration method, and, for selected samples, by FT-IR spectroscopy of adsorbed pyridine used as a probe for both Bronsted and Lewis acidity. A dependence of the acidity on the Al/Si atomic ratio was found. According to the X-ray diffraction patterns, all the oxides have an amorp…
Quantitative determination of surface area of silica gel particles by near infrared spectroscopy and chemometrics
2008
Abstract Surface areas of silica gel particles have been quantitatively determined by using near infrared spectrometry and chemometrics. Surface areas of six silica gel samples with varying surface area (300–750 m2/g) have been determined by the common Brunauer–Emmett–Teller (BET) method and used in preparing mixtures of silica gel samples with varying surface area in the ranges 300–474 and 500–750 m2/g. The near infrared spectra of the mixtures were measured and the spectral profiles calibrated against the calculated surface area of the mixtures as dependent variable using partial least squares (PLS) technique. The models obtained from the calibrations were then used in predicting the surf…
Application of TLC and GC-MS to the detection of capsaicin from hot peppers(Capsicum annuum)
2004
Capsaicin was extracted from red hot pepper (Capsicum annuum) fruits and from commercial red hot pepper powder and separated on silica gel 60 plates with concentration zone (Merck); toluene-acetone-chloroform, 45 + 30 + 25 ( v/v ), was used as mobile phase. Detection was performed by exposure to iodine vapor. The spots assumed to arise from capsaicin were removed from the plate and the components were extracted with chloroform. The extracts were analyzed by gas chromatography combined with mass spectrometry.
Determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin in goat milk and tissues by glass capillary gas chromatography and medium resolution mass fragme…
1981
Abstract An analytical method has been developed for the study of the elimination of 2,3,7,8-tetrachlodoribenzo-p-dioxin (TCDD) by lactation and its determination in various tissues of goat. The method is based on the alkaline hydrolysis of milk, liver, fat, muscle, blood, faeces and urine samples, extraction with n-hexane, treatment with sulphuric acid-saturated silica gel, chromatographic clean-up on silica gel and alumina micro-columns, and glass capillary gas chromatography—medium resolution mass fragmenography (resolution 2000). 1,2,3,4-Tetrachlorodibenzo-p-dioxin is used as the internal standard, the concentration of TCDD being determined from the calibration curve calculated from the…
C-28/C-30 oxidized cycloartanes from the leaves and twigs of Caloncoba dusenii Gilg
2021
Abstract Four hitherto unreported cycloartane-type triterpenes (1-4) with C-28/C-30 oxidized methyl groups together with two known compounds (5-6) have been obtained from the leaves and twigs of Caloncoba dusenii Gilg. The compounds were isolated through extraction and silica gel column chromatography. Their structures and relative stereochemistry were determined by extensive use of spectroscopic techniques including IR, 1D and 2D-NMR as well as mass spectrometry. This is the first report of C-28/C-30 oxidized positions in cycloartanes from nature.
Thin-layer chromatography of 2-methyl-4-chlorophenoxyacetic acid and its soil metabolites
1980
Abstract The thin-layer chromatography of 2-methyl-4-chlorophenoxyacetic acid, 4-chloro- o -cresol and 3-methyl-5-chlorocatechol and their pentafluorobenzyl derivatives has been studied on silica gel as adsorbent with 19 solvent systems. The best separation of the individual components occurred with toluene-benzene-acetic acid (2:2:1). Chloroform-diethyl ether-toluene (1:1:1) was suitable for the group separation of the pentafluorobenzyl derivatives.
The application of porous silica layers in open tubular columns for liquid chromatography
1987
Two methods to realize a porous retentive silica layer on the inner wall of 10–25 µm fused silica capillaries for OTLC, etching and precipitation of silica from solution, have been investigated. Etching of the fused silica capillaries with 1M KOH, creates an activated surface, but the capacity of the silica layer is too small to serve as retentive layer in OTLC. Better prospects are offered by the precipitation of silica from a solution of polyethoxysiloxane, dynamically coated on the inner wall of the fused silica capillary. It appears to be possible to deposite a porous silica layer up to 0.8 µm thick (in a 25 µm capillary) by this method, which seems to be suitable for liquid-solid an dy…
Column technology in liquid chromatography
2017
This chapter deals with the most important part of the liquid chromatography (LC) system: the column enabling the efficient and fast resolution of complex mixtures. It is divided into seven sections under the overall aspects of manufacture, operation, and evaluation of analytical columns for the user. The first three sections highlight the column design and hardware, followed by a thorough treatment of the properties of microparticulate silica adsorbents as packing material, stationary phases performed by surface functionalization, and the column filling process. Then, the implementation of the column into the LC system is discussed, leading into chromatographic column testing as a C18-bond…