Synthetic Evaporation Loss

Pyrethroids. More accurately described as the synthetic pyrethroids, this group of compounds has been used extensively in wood preservation for control of both beetles and termites. Activity, cost and performance characteristics vary depending upon the specific compound but most readily accepted for use in wood preservative formulations are permethrin, cypermethrin, deltamethrin, bifenthrin and cyfluthrin. In terms of activity against wood boring beetles, cyfluthrin is estimated to be 20 times more effective than permethrin, 10 times as effective as cypermethrin and twice as effective as deltamethrin when compared in laboratory evaluative procedures. However, in practice other factors need to be considered, particularly the relative vapour pressures (and therefore evaporative loss) and, in wood in soil contact, the rate of biotransformation by colonising bacteria. The pyrethroids are effective as neurotoxins, and are axonic poisons. 

In terms of flavorings, dry process flavorings (containing flavor enhancers and natural or synthetic top notes), dry vegetables, ground spices, and herbs as well as encapsulated or plated spices serve as the foundation of the flavor systems. Plated spice oils are not particularly stable and may be a problem in terms of oxidation or evaporative losses. The use of encapsulated essential oils offers greater stability, but they do not have very much intrinsic smell in the dry form and may be misjudged by the consumer in consequence. 

Ethoxyquin, a synthetic antioxidant, is not generally allowed for human consumption in foods, but it is being added to animal feed and to fruits as an antiscald agent (94,143). Ethoxyquin is also used in the spice industry to prevent carotenoid loss during postharvest handling. However, ethoxyquin-treated paprika is unacceptable for some markets and some consumers (129). Perfetti et al. (130) described a method for determination of ethoxyquin in paprika and chili powder. Ethoxyquin was extracted from the spice with hexane and partitioned into 0.3 N HC1. After adjusting the solution to pH 13-14, ethoxyquin was extracted into hexane, and the hexane layer was evaporated to dryness. An acetonitrile solution of the residue was then analyzed by reversed-phase HPLC, with detection at 254 nm. The mobile phase was water/acetonitrile with ammonium acetate buffer. Recoveries from samples fortified at 50, 100, and 200 ppm averaged 92%, with a coefficient of variation of 2.3%. The method was applied to a number of commercial samples of paprika and chili powder. Ethoxyquin was found in paprika samples at levels up to 63 ppm and in chili powder samples at levels up to 20 ppm. 

Among the new synthetic methodologies recently studied and exploited, the use of ionic liquids as solvent-catalysts to perform more environmentally friendly Friedel-Crafts acylations has been developed. In contrast to volatile organic solvents, ionic liquids have no measurable vapor pressure, and, therefore, fhere is no loss of solvent through evaporation. Moreover, ionic liquids can be easily recovered, cleaned, and reused for different runs. 

Zintl also found that the most convenient way to produce the solutions of the anionic clusters in liquid ammonia is to extract alkali metal/post-transition element alloys in the solvent. However, detailed solid-state characterization of the clusters is very difficult using this technique, since poorly crystalline and often pyrophoric solids are obtained once the solvent is evaporated. These troublesome solids are alkali-metal ammoniates of cluster ions, " of which only [Li(NH3)4]3-[Li2(NH3)2Sb5] -2NH3 seem to have been completely structurally characterized, Furthermore, the ammoniates most often slowly revert back to the alloy upon further loss of ammonia. The last step involves transfer of electrons from the strongly reducing cluster anion back to the alkali-metal ion and thus represents a major synthetic obstacle. 

Extraction of Phenolic Products. Reaction mixtures were acidified and extracted with ether (4 X 100 ml.). The combined ether extracts were evaporated to a small volume (1-2 ml.) and analyzed by gas-liquid chromatography. By using synthetic mixtures, this procedure was shown not to lead to preferential loss of any component. 

Debris recovered from the fire scene is often wet and burned, and may consist of material such as wood, carpet, carpet padding, tile, and other synthetic materials, all of which can contribute interfering volatile pyrolysis products that can make the identification of the accelerants difficult. The loss of accelerants through adsorption into the debris, evaporation from the heat of the blaze, and the presence of water all contribute to make the identification of accelerants a challenging task. GC can be a powerful tool in the analysis to separate and identify the accelerant in the presence of these interferences. Fultz and DeHaan have written an excellent chapter on GC in arson and explosive analysis (156). 

In the category of diluent, nonreactive adhesives, one example is model airplane cement (often cellulose nitrate in a mixture of ketones and aromatic solvents). As a coating we would call it a lacquer. Aqueous solutions of natural and synthetic gums are used in library paste. Some of the popular white glues for paper and wood are simply poly(vinyl acetate) emulsions with a small amount of plasticizer. All of these materials solidify after contacting the surface as a liquid by loss of solvent or diluent. Evaporation or diffusion into a porous substrate may be involved. 

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