Volatile solvents, use

As a further example of a dog s ability to discriminate certain solvents, it is believed that dogs searching for the explosive C-4 as a target substance may be detecting the presence of cyclohexanone rather that the explosive itself. For example, cyclohexanone is a volatile solvent used in the purification process for... 

Materials. All materials had the highest purity available. The synthetic lecithin, / ,y-dipalmitoyl-DL-a-glycerylphospnorylcholine, was obtained from the Sigma Chemical Co. Chloroform, the principal volatile solvent used for spreading, was obtained from the Bojin Pharmaceutical Chemical Laboratories. Twice-distilled benzene was used for some of the experiments with related materials. Film-balance measurements with the solvents alone showed that remaining impurities were negligible. 

The evaporative light-scattering detector (ELSD) is a near universal detector suitable for the determination of (mainly) neutral compounds that are less volatile than the mobile phase used for the separation [151,152]. Primary uses include the detection of compounds with a weak response to the UV detector, especially carbohydrates, lipids, surfactants, polymers and petroleum products. Its greater sensitivity and ease of use in gradient elution separations makes it preferable to the refractive index detector for these applications. The ELSD is compatible with most volatile solvents used for normal and... 

Gloss oil n. Solution of limed rosin or lined rosin acids in a volatile solvent, used chiefly in surface coatings (when made from tall oil, the source is usually indicated). 

Plastic wood n. A paste of wood flour, plasticizer, resins and/or other materials dispersed in nitrocellulose or other binders and volatile solvents, used for repairing or filling holes in wood, etc. 

Steam baths are especially well suited as heat sources for the safe evaporation of volatile solvents used for a reaction or extraction (Sec. 2.29) or when purifying a solid product by recrystallization (Sec. 3.2). As an alternative to working at a hood, an inverted funnel attached to a vacuum source may be placed over the top of the container (Fig. 2.30c) to remove vapors and keep them from entering the room. 

Baltruschat, H., Kamphauser, I., Oelgeklaus, R., Rose, J and Wahlkamp, M. (1997) Detection of volatile solvents using potentiodymanic gas sensors. Anal. Chem., 69, 743-748. 

The material of interest is dissolved in a volatile solvent, spread on the surface and allowed to evaporate. As the sweep moves across, compressing the surface, the pressure is measured providing t versus the area per molecule, a. Care must be taken to ensure complete evaporation [1] and the film structure may depend on the nature of the spreading solvent [78]. When the trough area is used to calculate a, one must account for the area due to the meniscus [79]. Barnes and Sharp [80] have introduced a remotely operated barrier drive mechanism for cleaning the water surface while maintaining a closed environment. 

All glassware should be scrupulously clean and, for most purposes, dry before being employed in preparative work in the laboratory. It is well to develop the habit of cleaning all glass apparatus immediately after use the nature of the dirt will, in general, be known at the time, and, furthermore, the cleaning process becomes more difficult if the dirty apparatus is allowed to stand for any considerable period, particularly if volatile solvents have evaporated in the meantime. 

The efficiency of separation of solvent from solute varies with their nature and the rate of flow of liquid from the HPLC into the interface. Volatile solvents like hexane can be evaporated quickly and tend not to form large clusters, and therefore rates of flow of about 1 ml/min can be accepted from the HPLC apparatus. For less-volatile solvents like water, evaporation is slower, clusters are less easily broken down, and maximum flow rates are about 0.1-0.5 ml/min. Because separation of solvent from solute depends on relative volatilities and rates of diffusion, the greater the molecular mass difference between them, the better is the efficiency of separation. Generally, HPLC is used for substances that are nonvolatile or are thermally labile, as they would otherwise be analyzed by the practically simpler GC method the nonvolatile substances usually have molecular masses considerably larger than those of commonly used HPLC solvents, so separation is good. 

Liquids examined by FAB are introduced into the mass spectrometer on the end of a probe inserted through a vacuum lock in such a way that the liquid lies in the target area of the fast atom or ion beam. There is a high vacuum in this region, and there would be little point in attempting to examine a solution of a sample in one of the commoner volatile solvents such as water or dichloromethane because it would evaporate extremely quickly, probably as a burst of vapor when introduced into the vacuum. Therefore it is necessary to use a high-boiling solvent as the matrix material, such as one of those listed in Table 13.1. 

Genera.1 Ca.se, The simple adiabatic model just discussed often represents an oversimplification, since the real situation implies a multitude of heat effects (/) The heat of solution tends to increase the temperature and thus to reduce the solubihty. 2) In the case of a volatile solvent, partial solvent evaporation absorbs some of the heat. (This effect is particularly important when using water, the cheapest solvent.) (J) Heat is transferred from the hquid to the gas phase and vice versa. (4) Heat is transferred from both phase streams to the shell of the column and from the shell to the outside or to cooling cods. 

Solventless Extrusion Process. The solvendess process for making double-base propellants has been used ia the United States primarily for the manufacture of rocket propellant grains having web thickness from ca 1.35 to 15 cm and for thin-sheet mortar (M8) propellant. The process offers such advantages as minimal dimensional changes after extmsion, the elimination of the drying process, and better long-term baUistic uniformity because there is no loss of volatile solvent. The composition and properties of typical double-base solvent extmded rocket and mortar propellant are Hsted ia Table... 

Extrusion Processes. Polymer solutions are converted into fibers by extmsion. The dry-extmsion process, also called dry spinning, is primarily used for acetate and triacetate. In this operation, a solution of polymer in a volatile solvent is forced through a number of parallel orifices (spinneret) into a cabinet of warm air the fibers are formed by evaporation of the solvent. In wet extmsion, a polymer solution is forced through a spinneret into a Hquid that coagulates the filaments and removes the solvent. In melt extmsion, molten polymer is forced through a multihole die (pack) into air, which cools the strands into filaments. 

Pulp-like olefin fibers are produced by a high pressure spurting process developed by Hercules Inc. and Solvay, Inc. Polypropylene or polyethylene is dissolved in volatile solvents at high temperature and pressure. After the solution is released, the solvent is volatilised, and the polymer expands into a highly fluffed, pulp-like product. Additives are included to modify the surface characteristics of the pulp. Uses include felted fabrics, substitution in whole or in part for wood pulp in papermaking, and replacement of asbestos in reinforcing appHcations (56). 

Enclosed agitated filters are useful when volatile solvents are in use or when the solvent gives off toxic vapor or fume. Another significant advantage is that their operation does not require any manual labor. Control can be manual or automatic, usually by timers or by specific measurements of the product. Most filters are made of mild steel, with the exposed surfaces protected by lead, tile, mbber lining, or by coating or spraying with other substances as necessary. Filtration areas up to 10 m are available and the maximum cake thickness is 1 m. Apphcations are mainly in the chemical industry for the recovery of solvents. 

These solvents differ in volatility and selectivity for the removal of H2S, mercaptans, and CO2 from gases of different composition. Other alkaline solvents used for the absorption of acidic components in gases include potassium carbonate, K CO, solutions combined with a variety of activators and solubilizers to improve gas—Hquid contacting. 

Bonded Solid-Film Lubricants. Although a thin film of soHd lubricant that is burnished onto a wearing surface often is useful for break-in operations, over 95% are resin bonded for improved life and performance (62). Use of adhesive binders permits apphcations of coatings 5—20 p.m thick by spraying, dipping, or bmshing as dispersions in a volatile solvent. Some commonly used bonded lubricant films are Hsted in Table 12 (62) with a more extensive listing in Reference 61. 

QuaHty control in the production of organic solvent finish removers may be done by gas—Hquid chromatography, which allows the manufacturer to determine the actual ratio of volatile solvent present in the finished product. If the product does not meet specifications, solvents can be added to bring the product to an acceptable composition. A less expensive approach is to use a hydrometer to determine the specific gravity of the product. The specific gravity indicates if the proper blend has been reached. Nonaqueous acid—base titration may be used to determine the amount of acid or alkaline activator present in a remover. 

Novolak Resins. In a conventional novolak process, molten phenol is placed into the reactor, foHowed by a precise amount of acid catalyst. The formaldehyde solution is added at a temperature near 90°C and a formaldehyde-to-phenol molar ratio of 0.75 1 to 0.85 1. For safety reasons, slow continuous or stepwise addition of formaldehyde is preferred over adding the entire charge at once. Reaction enthalpy has been reported to be above 80 kj /mol (19 kcal/mol) (29,30). The heat of reaction is removed by refluxing the water combined with the formaldehyde or by using a small amount of a volatile solvent such as toluene. Toluene and xylene are used for azeotropic distillation. FoHowing decantation, the toluene or xylene is returned to the reactor. 

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