Showing papers on "Silica gel published in 1973"
TL;DR: A unique colorimetric method for the quantitative determination of phospholipids that does not involve the acid digestion of the lipid is described and it followed Beer's law in the range of 1-10 micro g ofospholipid phosphorus.
437 citations
TL;DR: The quantitative spectrophotometric determination of the Substance is carried out by transferring the sorbent area containing the spot into a test-tube and using the Folin-Ciocalteu reagent, without the necessity for carrying out a prior elution for the recovery of the substance.
241 citations
TL;DR: Aminopropyl silica gel made by treating chromatographic grades of silica with 3-aminopropylon triethoxy silane, is reacted with p-nitrobenzoyl chloride and the −NO2 group reduced to −NH2 with sodium dithionite as discussed by the authors.
113 citations
TL;DR: A column packing for high-performance liquid chromatography, porous microspheres of silica produced by the agglutination of colloidal silica particles, has recently been introduced for use in adsorption chromatography.
71 citations
01 Jan 1973
TL;DR: The methoxylation process of a silica gel (Aerogel) surface pretreated at 110°C in vacuum occurs between 150 and 190°C simultaneously through the esterification of the silanol group (k 2 ) and through the opening of siloxane bridges (k 1 ) as mentioned in this paper.
Abstract: The methoxylation process of a silica gel (Aerogel) surface pretreated at 110°C in vacuum occurs between 150 and 190°C simultaneously through the esterification of the silanol group ( k 2 ) and through the opening of siloxane bridges ( k 1 ) in such a way that ( k 1 k 2 )=0.331 at 150°C and ( k 1 k 2 )=0.644 at 190°C At lower temperature the esterification reaction is thus favored. The maximum number of −CH 3 grafted on the surface is of the order of the monolayer content of physically adsorbed methanol. It seems that the protonated CH 3 OH 2 + species is an important intermediate in the methoxylation reaction since the order of magnitude of k 1 and k 2 may be derived from the ratio of the lifetime of a molecule on an adsorption site to the lifetime of the protonmethanol association.The rate process observed by infrared spectroscopy using the development of the asymetric C-H stretching band is limited by diffusion, as opposed to what has been observed for the powder. Aerogel seems to be very sensitive to an “internal sintering process” observed under mild drying conditions and which effects the narrow pores.
54 citations
TL;DR: In this article, the 13C NMR chemical shift anisotropy powder patterns under conditions of proton decoupling have been determined for benzene (13C enriched) adsorbed on charcoal and silica gel and for toluene adaption on charcoal.
Abstract: The 13C NMR chemical shift anisotropy powder patterns under conditions of proton decoupling have been determined for benzene (13C enriched) adsorbed on charcoal and silica gel and for toluene adsorbed on charcoal. These spectra do not differ significantly from those of the pure solid as far as principal values of the chemical shift tensor are concerned. The simultaneous presence of molecules in various states of motional narrowing of the anisotropy powder pattern is revealed, in agreement with earlier observations of dipolar broadened proton spectra for similar systems. Motional narrowing effects observable for the toluene molecule in the adsorbed state aid in the assignment of principal axes.
52 citations
TL;DR: In this article, the initial contact of WO3 on silica gel with propylene, significant increases in disproportionation activity were observed for periods of up to 24 hours, and the rate of approach to steady state activity was found to depend on both temperature and pressure.
43 citations
TL;DR: In this article, the surface water content of silica gel, magnesium oxide, zinc oxide, and titanium dioxide was determined using active hydrogen analysis and successive-ignition loss method.
Abstract: The surface water content has been determined on silica gel, magnesium oxide, zinc oxide, and titanium dioxide by means of active hydrogen analysis and by the successive-ignition-loss method. Excep...
42 citations
TL;DR: In this paper, the authors investigated the isomerization at 100 and 200 °C in hydrogen carrier of 1-hexene, 2-methyl-1-pentene, and 2-ethyl-1butene on various silica gels activated in oxygen at 500 °C and then hydrogen at 400 °C.
42 citations
TL;DR: In this paper, a bidimensional system for the separation of nucleosides and derivatives is described, which may be used for the extraction of radioproducts resulting from the action of γ-rays on thymidine.
39 citations
TL;DR: In this paper, the EPR spectrum of 17O− on partially reduced molybdenum oxide supported on silica-gel has been observed following adsorption of N2O at room temperature.
TL;DR: It is suggested that the membrane separates two aqueous phases of different structure, and that the enhanced structure of cell water contributes to the observed ionic distributions.
Patent•
10 Jan 1973TL;DR: In this paper, high pore volume silica materials are used as thickening, reinforcing, and flatting agents, using a water soluble silica desolubilizing agent selected from the group consisting of ammonia, monohydric alcohols, glycols, ketones and salts.
Abstract: High pore volume silica materials are useful as thickening, reinforcing and flatting agents This invention comprises selectively forming silica gels having pore volumes in the range of 12 to 30 cc/g These high pore volume silica gels can be produced by the alkaline gelation of a mixture of silicate and ammonium hydroxide at a pH of from 106 to 112, using a water soluble silica desolubilizing agent selected from the group consisting of ammonia, monohydric alcohols, glycols, ketones and salts The silica is then aged, neutralized, optionally aged a second time, filtered and washed This silica may then be dried and directly used, or it may be milled to a smaller size For use as a thickening agent, the silica is milled in a fluid energy mill to an average particle size of less than about 1 micron, and preferably to less than 05 micron
TL;DR: The activity of a silica gel is determined by its pore system, the surface quality of the frame substance, and the saturation grade of the silanol groups with water.
TL;DR: In this article, the spectra observed by the interaction of oxygen and the surface were found to be composed of spectra due to two different species, which were identified with O2− chemisorbed on metallic silver by a comparison of the observed g values and other features with those previously reported.
Abstract: The state of adsorbed oxygen on metallic silver dispersed on silica gel has been studied by ESR The spectra observed by the interaction of oxygen and the surface were found to be composed of spectra due to two different species One of the species, which was formed separately by the contact with oxygen at −110 °C, was identified with O2− chemisorbed on metallic silver by a comparison of the observed g values and the other features with those previously reported The other species has a doublet at g=2036 This spectrum was reproduced by the interaction of N2O with the silver surface Further, the γ-irradiation of the silver samples in the presence of O2 and N2O markedly enhanced the intensity of this spectrum, showing a low-field hump On the basis of the g values and the splitting of the high-field doublet, assuming that the doublet is due to the hyperfine interaction of an unpaired electron with the silver nucleus, the species was assigned to Ag2+ in the present system It is postulated that this speci
TL;DR: A new assay procedure using quantitative thin-layer chromatography has been developed for trimethoprim and its four major free and conjugated metabolitres based upon the measurement of the fluorescence which develops for these compounds on non-fluorescing silica gel plates.
TL;DR: In this paper, the initial rate data were obtained for the disproportionation of propylene over a 10% WO3 on silica gel catalyst, and the experimental data were well correlated by assuming that a dual-site surface reaction was the rate-controlling step in the reaction mechanism.
TL;DR: The stability of unsaturated methyl esters of fatty acid adsorbed on silica gel and silicic acid was studied by gas liquid chromatographic estimation of disappearance relative to a saturated internal standard.
Abstract: The stability of unsaturated methyl esters of fatty acid adsorbed on silica gel and silicic acid was studied by gas liquid chromatographic estimation of disappearance relative to a saturated internal standard. Variables included silica-ester ratio, agitation, adsorbent particle size, and degree of unsaturation. Under the conditions of the experiment, destruction of substrate unsaturated ester at 80 C was more a function of time than of unsaturation or initial purity.
TL;DR: A number of fluorescent pesticides, namely, benomyl, coumatetralyl, diphacinone, fuberidazole, propyl isome and quinomethionate, have been investigated on silica gel thin-layer chromatograms and the effects of heat treatment on the fluorescence have been observed.
TL;DR: A simplified and relatively rapid method, based on a gas chromatographic determination preceded by a thin-layer chromatography, for the separation of heterocyclic nitrogen compounds in atmospheric particulate matter has been developed.
TL;DR: In this article, the lifetime spectra of positrons annihilating in silica gels of various pore sizes as a function of temperature are investigated, and two long lifetime components are attributed to the annihilation of o-Ps under various processes.
Abstract: The lifetime spectra of positrons annihilating in silica gels of various pore sizes as a function of temperature are investigated. There are two long lifetime components which are attributed to the annihilation of o-Ps under various processes. The intensities of the two long lifetime components change with temperature. These changes cannot be attributed solely to the diffusion process. Other processes, such as the formation, quenching, and thermalization of o-Ps in silica gels, must also be taken into consideration.The mean life of the longest lifetime component also changes with temperature. The pattern of this change varies with the pore size and grain size of the silica gel. It seems that positronium atoms are adsorbed on the pore surface of silica gels. A potential model including the effect of adsorption is proposed to explain this phenomenon. The change of annihilation rate of o-Ps is not found to be solely due to the vibration of surface atoms. The quenching due to the presence of the "strained" su...
TL;DR: The use of organic gels for crystal growth has not received wide attention partially due to a statement in the literature stating that organic Gels are "protective gels" which inhibit crystal growth as discussed by the authors.
TL;DR: A thin-layer chromatographic method is described for polyhedric diterpene acetates derived from irritant and co-carcinogenic principles from the Croton and Euphorbia genera of the family Euphorbiaceae that provides a rapid micro-screening procedure for these diterpenes.
TL;DR: In this paper, a general equation relating column performance as a function of important experimental variables is described, and experimental data obtained from studies of effects of particle diameter (dp) on efficiency, permeability, and shape of HETP vs. velocity curves for porous silica gel and alumina adsorbents of 5 ⩽ dp⩽ 40 μm gave a better understanding of the role of new small dp packings in high-performance liquid chromatography.
Patent•
15 Oct 1973TL;DR: In this article, a method of producing the silica-containing support for a polymerization catalyst was proposed, which involves precipitating the hydrogel employing an ammonium salt and removing the water from the water by employing an oxygen-containing organic compound.
Abstract: A method of producing the silica-containing support for a polymerization catalyst which involves precipitating the silica hydrogel employing an ammonium salt and removing the water from the hydrogel by employing an oxygen-containing organic compound.
TL;DR: In this paper, it is shown that surface diffusion is dependent on temperature and concentration and that an additional quantity is influencing diffusivity in such a system, which is analogous to gradient dependency of viscosity, both being deducible from Eyrings theory of rate processes.
TL;DR: From data collected, a two-dimensional thin-layer chromatographic system has been developed that satisfactorily resolves a mixture of the fourteen methylated bases employed in this investigation.
Patent•
18 May 1973
TL;DR: A very effective flatting agent for varnishes and lacquer is a silica gel which has been melt-coated with a miscible mixture of a wax and an organic fatty acid as mentioned in this paper.
Abstract: A very effective flatting agent for varnishes and lacquers is a silica gel which has been melt-coated with a miscible mixture of a wax and an organic fatty acid. The wax and the fatty acid should have a melting point above about 40 DEG C, with the melting point of the wax and the fatty acid being less than the decomposition point of either of these components. The silica gel has an average particle size between about 2 microns and 10 microns, and preferably has a very narrow particle size distribution. When admixed into a lacquer or varnish, these silica gels create a light diffusing surface which gives the visual effect of a dull finish.