Search results for "silica gel"
showing 10 items of 91 documents
Thin-layer chromatography of chlorinated anisoles and veratroles
1989
The thin-layer chromatography of chlorinated anisoles (methoxybenzenes) and veratroles (1,2-dimethoxybenzenes) has been examined on silica gel G60 and RP-18 thin-layer plates. More than fifty solvent systems were screened and some of them recommended for particular separations. Acetone was shown to be suitable for group separation of both chlorinated anisoles and veratroles on a silica gel G60 stationary phase having a very narrow range of RF values. On the other hand, benzene, dichloromethane and the various mixtures of light petroleum (b.p. 40–60°C) and a more polar eluent (such as diethyl ether, acetone or ethyl acetate) were recommended for separation of certain individual isomers. The …
Impact of the post-treatment conditions of parent silica on the silanization of n-octadecyl bonded silica packings in reversed-phase high-performance…
2001
Native mesoporous silica beads were subjected to a sequence of post-treatment procedure including hydrochloric acid treatment, calcination and subsequent rehydroxylation. The post-treated silica beads were converted into RP-18 silica by silanization with monochloro- and dimethoxy-n-octadecylsilanes, respectively. The influence of post-treatments and silanization conditions on the physico-chemical characteristics and on the chromatographic behaviour of the RP-silicas was studied. Also the changes of the pore structural parameters and the silanol group densities during the post-treatment and silanization were assessed.
Quality control of commercial mustard by thin-layer chromatography
2005
Horseradish samples ( Cochlearis armoracia L. ) and mustard samples ( Sinapis alba L. ) were extracted with 70:30 ( v/v ) methanol-water in accordance with ISO method 91671. Samples of commercial mustard with and without horseradish were submitted to the same extraction procedure. Separation of the active compounds from these samples were performed on silica gel 60 plates with preconcentration zone and on silica gel F 254 high-performance thin-layer chromatography plates, with iso -propanol-25% ammonia, 90 + 10 ( v/v ), containing different volumes of distilled water (1, 2, 3, or 5 parts), as mobile phases. After development the compounds were visualized in UV light at λ = 254 nm or by expo…
Synthesis of the aggregation pheromone of the Colorado potato beetle from its degradation product
2015
Incubation of the Colorado potato beetle aggregation pheromone, (S)-1,3-dihydroxy-3,7-dimethyl-6-octen-2-one, with antennal or leg extracts from this beetle gave 6-methyl-5-hepten-2-one as the major product. This ketone was used as a substrate in a stereoselective synthesis of the pheromone. It was attached to the butanediacetal of glycolic acid with good stereoselectivity and the desired isomer was further enriched by purification of the product of this reaction on silica gel.
Comparing encapsulation-dehydration and droplet-vitrification for cryopreservation of sugarcane (Saccharum spp.) shoot tips
2011
Abstract In this study, in vitro shoot tips of two sugarcane clones were successfully cryopreserved using encapsulation-dehydration and droplet-vitrification with two vitrification solutions, PVS2 and PVS3. For both clones, encapsulation-dehydration induced significantly higher recovery, reaching 60% for clone H70-144 and 53% for clone CP68-1026, compared with droplet-vitrification in which recovery was 33–37% for clone H70-144 and 20–27% for clone CP68-1026. Optimal conditions included preculture of encapsulated shoot apices for 24 h in liquid medium with 0.75 M sucrose and dehydration with silica gel to 20% moisture content (fresh weight basis) before direct immersion in liquid nitrogen. …
Response ofBacillus subtilis spores to dehydration and UV irradiation at extremely low temperatures
1996
Spores of Bacillus subtilis have been exposed to the conditions of extreme dehydration (argon/silica gel; simulated space vacuum) for up to 12 weeks at 298 K and 80 K in the dark. The inactivation has been correlated with the production of DNA-double strand-breaks. The temperature-dependence of the rate constants for inactivation or production of DNA-double strand-breaks is surprisingly low. Controls kept in the frozen state at 250 K for the same period of time showed no sign of deterioration. In another series of experiments the spores have been UV irradiated (253.7 nm) at 298 K, 200 K and 80 K after exposure to dehydrating conditions for 3 days. Fluence-effect relationships for inactivati…
Salt drying: a low-cost, simple and efficient method for storing plants in the field and preserving biological repositories for DNA diversity researc…
2013
Although a variety of methods have been optimized for the collection and storage of plant specimens, most of these are not suited for field expeditions for a variety of logistic reasons. Drying specimens with silica gel in polyethylene bags is currently the standard for field-sampling methods that are suitable for subsequent DNA extraction. However, silica-gel repositories are not readily available in remote areas, and its use is not very cost-effective for the long-term storage of collections or in developing countries with limited research budgets. Salting is an ancient and traditional drying process that preserves food samples by dehydrating tissues and inhibiting water-dependent cellula…
Simplified models for the performance evaluation of desiccant wheel dehumidification
2002
In the present communication, simple models have been presented to evaluate the performance of rotary desiccant wheels based on different kind of solid desiccants e.g. silica gel and LiCl. The first part of the paper presents ‘Model 54’ which is developed for silica gel desiccant rotor. The model has been derived from the interpolation of experimental data obtained from the industry and the correlations have been developed for predicting outlet temperature and absolute humidity. The ‘Model 54’ consists of 54 coefficients corresponding to each correlation for outlet absolute humidity and temperature and it is found that the model predicts very well the performance of silica gel desiccant rot…
Experimental results on adsorption beds for air dehumidification
2016
Desiccant rotors are commonly used in large scale solar cooling open cycle applications. As is well known, adsorption heat sensibly reduces the dehumidification capacity of the desiccant material and results in lower system performance. The aim of this work is to describe an innovative solution that permits simultaneous mass and heat transfer. In particular, two components working with silica gel fixed beds were studied and compared. The first component is a simple packed bed containing silica gel grains. The second component is a fin and tube heat exchanger commonly used in several air conditioning applications wherein the spaces between the fins are filled with silica gel grains. In this …
Analysis of Polycyclic Aromatic Hydrocarbons and Their Oxygen-Containing Derivatives and Metabolites in Soils
2010
Although polycyclic aromatic hydrocarbons (PAHs) have been extensively studied, the knowledge of their oxygen-containing derivatives and metabolites (OPAHs) in soils is limited. We modified and tested an existing analytical protocol involving pressurized liquid extraction of soil followed by fractionation of target compounds into PAHs and OPAHs on a silica gel column and gas chromatography/ mass spectrometry-based separation and quantification. Polycyclic aromatic hydrocarbons and carbonyl-OPAHs were quantified directly after separation on silica gel columns, and hydroxyl/carboxyl-OPAHs were quantified after silylation with N,O-bis(trimethylsilyl)trifluoroacetamide. Recoveries between 78 an…