Trace amounts

Normally absent or in trace amounts in crude oil, products of conversion processes such as diolefins, acetylenes, etc., are encountered. Table 1.4 gives the physical properties of some of them. Noteworthy is 1-3 butadienerC ( l)... 

In a conventional gasoline containing hydrocarbons or even ethers, the presence of water is not a problem in fact, water is totally soluble up to about 50 ppm at ambient temperature. Beyond this value water separates without affecting the hydrocarbon phase and the water leg can be withdrawn if necessary. On the other hand, in the presence of alcohols (ethanol and especially methanol), trace amounts of water can cause a separation of two phases one is a mixture of water and alcohol, the other of hydrocarbons (Cox, 1979). 

Behm R J, Hotios J and Magnussen O M 1995 Effect of trace amounts of Ci in Cu underpotentiai deposition on Au(111) in perchiorate soiutions An in s/fu scanning tunneiing microscopy study Surf. Sc/. 335 129-44... 

ASARONE 70-80% of calamus oil. In trace amounts in Asian carrot seed and clove bud oils. 

EUGENOL In very large amounts in bay, cinnamon, clove and pimento oils. In goodly amounts in basil, eucalyptus and tejpat. Lots of trace amounts in many other oils. 

Indene derivatives 264a and 264b are formed by the intramolecular reaction of 3-methyl-3-phenyl-l-butene (263a) and 3,3,3-triphenylpropylene (263b) [237]. Two phenyl groups are introduced into the /3-substituted -methylstyrene 265 to form the /3-substituted /3-diphenylmethylstyrene 267 via 266 in one step[238]. Allyl acetate reacts with benzene to give 3-phenylcinnamaldehyde (269) by acyl—O bond fission. The primary product 268 was obtained in a trace amount[239]. 

Lithiomethylthiazole (162) adds to unmetalated 2-methylthiazole (161), which needs be present in only trace amounts, generating adduct... 

Unless the p keto ester can form a stable anion by deprotonation as m step 4 of Figure 21 1 the Claisen condensation product is present m only trace amounts at equi librium Ethyl 2 methylpropanoate for example does not give any of its condensation product under the customary conditions of the Claisen condensation... 

Ethyl 2 2 4 tnmethyl 3 oxopentanoate (cannot form a stable anion formed in no more than trace amounts)... 

Water of crystallation (solid state spectra) 3600-3100 (w) Usually a weak band at 1640-1615 cm also. Water in trace amounts in KBr disks shows a broad band at 3450 cm k... 

The focus of this chapter has been the evaluation of analytical data, including the use of statistics. In this final section we consider how statistics may be used to characterize a method s ability to detect trace amounts of an analyte. 

What is the effect on the analysis if the NH4Fe(S04)2 used to prepare the mediator solution is contaminated with trace amounts of Fe + ... 

Noncnzymc-Catalyzcd Reactions The variable-time method has also been used to determine the concentration of nonenzymatic catalysts. Because a trace amount of catalyst can substantially enhance a reaction s rate, a kinetic determination of a catalyst s concentration is capable of providing an excellent detection limit. One of the most commonly used reactions is the reduction of H2O2 by reducing agents, such as thiosulfate, iodide, and hydroquinone. These reactions are catalyzed by trace levels of selected metal ions. Eor example the reduction of H2O2 by U... 

A second use of arrays arises in the detection of trace components of material introduced into a mass spectrometer. For such very small quantities, it may well be that, by the time a scan has been carried out by a mass spectrometer with a point ion collector, the tiny amount of substance may have disappeared before the scan has been completed. An array collector overcomes this problem. Often, the problem of detecting trace amounts of a substance using a point ion collector is overcome by measuring not the whole mass spectrum but only one characteristic m/z value (single ion monitoring or single ion detection). However, unlike array detection, this single-ion detection method does not provide the whole spectrum, and an identification based on only one m/z value may well be open to misinterpretation and error. 

Determination of Water in DMAC. DMAC is hygroscopic and precautions must be taken to minimize exposure to the atmosphere. Trace amounts of water can be deterrnined by the Kad-Fischer method. 

Numerous methods for the deterrnination of monomer purity, including procedures for the deterrnination of saponification equivalent and bromine number, specific gravity, refractive index, and color, are available from manufacturers (68—70). Concentrations of minor components are deterrnined by iodimetry or colorimetry for HQ or MEHQ, by the Kad-Eisher method for water, and by turbidity measurements for trace amounts of polymer. 

Fluorine, which does not occur freely in nature except for trace amounts in radioactive materials, is widely found in combination with other elements, accounting for ca 0.065 wt % of the earth s cmst (4). The most important natural source of fluorine for industrial purposes is the mineral fluorspar [14542-23-5] CaF2, which contains about 49% fluorine. Detailed annual reports regarding the worldwide production and reserves of this mineral are available (5). A more complete discussion of the various sources of fluorine-containing minerals is given elsewhere (see Fluorine compounds, inorganic). 

Nonmeta.ls, Sulfur reacts with fluorine to yield the remarkably stable sulfur hexafluoride, SF. Operating conditions must be controlled because a mixture of the lower fluorides such as disulfur difluoride [13709-35-8] 2 2 disulfur decafluoride [5714-22-7] 2 10 sulfur tetrafluoride [7783-60-0] SF4, may also be formed. When this reaction is carried out between 310 and 340°C, SF is primarily obtained and essentially no SF and only trace amounts of lower fluorides. Below 300°C, and preferably at ca 275°C, SF is the primary product. At 450—500°C, a mixture comprising ca 50% SF and the lower sulfur fluorides is formed (see Fluorine compounds, inorganic-sulfur). 

A large number of by-products are formed in this process, mostly in trace amounts more significant quantities are obtained of hexafluoropropylene, perfluorocyclobutane, l-chloro-l,l,2,2-tetrafluoroethane, and 2-chloro-l,l,l,2,3,3-hexafluoropropane. Small amounts of highly toxic perfluoroisobutylene, CF2=C(CF2)2, are formed by the pyrolysis of chlorodifluoromethane. 

The common hemiceUulose components of arborescent plants are listed in Table 3. Xylans, arabinogalactans, and pectic substances are common to all while only traces (if at all) of glucomaimans are found in the cell walls of bamboo. Other polysaccharides are found in trace amounts in wood as well as in bark, growing tissues, and other specialized parts of trees. 

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