Compounds chemical separation

Eor products having relatively low specific activity, such as some compounds labeled with and which are synthesized on the scale of several millimoles, classical organic chemical separation methods may be utilized, including extraction, precipitation, and crystallization. Eor separation of complex mixtures and for products having high specific activity, such as those labeled with tritium, etc, chromatographic methods utilizing paper, thin... 

A liquid chromatography-mass spectrometry (LC-MS) method that can quantitatively analyze urinar y normal and modified nucleosides in less than 30 min with a good resolution and sufficient sensitivity has been developed. Nineteen kinds of normal and modified nucleosides were determined in urine samples from 10 healthy persons and 18 breast cancer patients. Compounds were separ ated on a reverse phase Kromasil C18 column (2.1 mm I.D.) by isocratic elution mode using 20 mg/1 ammonium acetate - acetonitrile (97 3 % v/v) at 200 p.l/min. A higher sensitivity was obtained in positive atmospheric pressure chemical ionization mode APCI(-i-). 

It was assumed throughout that the compound which separated out from the solution was chemically pure, but this is not always the case. The purity of the precipitate depends inter alia upon the substances present in solution both before and after the addition of the reagent, and also upon the exact experimental conditions of precipitation. In order to understand the influence of these and other factors, it will be necessary to give a short account of the properties of colloids. 

Both alkyl and aryl metals have been studied, but not a very wide range of compounds. Several studies of triphenylarsene and triphenylstibine have been done. Methyl and ethyl compounds of arsenic, germanium, mercury, bismuth, and lead essentially complete the list. In virtually all cases the results have been clouded by difficulties in effecting chemical separation without altering the product distribution. The results do, nonetheless, lead to valid and important conclusions. 

Chemical separations may first be accomplished by partitioning on the basis of polarity into a series of solvents from non-polar hexane to very polar compounds like methanol. Compounds may also be separated by molecular size, charge, or adsorptive characteristics, etc. Various chromatography methods are utilized, including columns, thin layer (TLC) gas-liquid (GLC), and more recently, high pressure liquid (HPLC) systems. HPLC has proven particularly useful for separations of water soluble compounds from relatively crude plant extracts. Previously, the major effort toward compound identification involved chemical tests to detect specific functional groups, whereas characterization is now usually accomplished by using a... 

The plutonium concentration in marine samples is principally due to environmental pollution caused by fallout from nuclear explosions and is generally at very low levels [75]. Environmental samples also contain microtraces of natural a emitters (uranium, thorium, and their decay products) which complicate the plutonium determinations [76]. Methods for the determination of plutonium in marine samples must therefore be very sensitive and selective. The methods reported for the chemical separation of plutonium are based on ion exchange resins [76-80] or liquid-liquid extraction with tertiary amines [81], organophosphorus compounds [82,83], and ketones [84,85]. 

The same group reported in 1986 a sensitive and selective HPLC method employing CL detection utilizing immobilized enzymes for simultaneous determination of acetylcholine and choline [187], Both compounds were separated on a reversed-phase column, passed through an immobilized enzyme column (acetylcholine esterase and choline oxidase), and converted to hydrogen peroxide, which was subsequently detected by the PO-CL reaction. In this period, other advances in this area were carried out such as the combination of solid-state PO CL detection and postcolumn chemical reaction systems in LC [188] or the development of a new low-dispersion system for narrow-bore LC [189],... 

Chemical separation of conjugated dienes and other polyunsaturated hydrocarbons is based on the availability of tt delocalized electrons. The use of a strong dienophile (e.g. tetracyanoethylene, TCNE) will derivatize only conjugated dienes, thus separating the polyunsaturated compounds into two groups. However, such derivatization is not always reversible since a retro-Diels-Alder reaction may require a high temperature. Hence, the retrieved compounds may be the thermostable ones and not those present in the initially analysed mixture. 

Many substances are not initially appropriate for gas chromatography because of their relatively high boiling points or insolubility. In such cases it is often possible to modify the compound chemically and render it more amenable to separation. In some instances, the chemical modification is used to enable easier detection of the compound, e.g. the introduction of a halogen for use with electron capture detectors. 

Chemical separation may be considered (acid treatment, leaching) when the parts to be removed are more reactive than the compound to be isolated and can be dissolved and washed away. A special case may be the electrolytic extraction when, in a solidified sample, there is sufficient electrochemical difference between the various phases an example is the extraction from Al-rich ingots of compounds such as CrAl7 and MnAl6 (Raynor and Wakeman 1947). 

Illustrative of the results which might be expected in using macro-cyclic compounds to separate cations having similar chemical properties in biological systems is the report of Muller (49) involving removal of 85Sr from rats using the bicyclic amine synthesized by Dietrich et al. 

The liquid waste must be pumpable. Contaminants must be in particulate form, or it must be possible to precipitate dissolved contaminants such as metal ions chemically. Separation must provide an advantage. The EPOC microfiltration technology does not remove volatile organic compounds (VOCs) from liquids. The unit s operation is affected by cold weather. 

The synthesis of a-branched amines caught our attention, as these compounds exhibit parhcular biological activity. In several of our ongoing projects involving the synthesis of biologically achve compounds, we required the asymmetric synthesis of a-branched chiral amines. a-Branched amines can be prepared by various routes, all performed in an asymmetric fashion. Currently, enzymatic and chemical separation of racemic a-branched amines and also diastereoselective methods still play a major role on an industrial scale [25]. However, due to poor separation by the latter methods and for economic reasons, catalytic approaches will be favored. 

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