THE QUESTION OF PURITY

Solvents and substances that are specified as pure for a particular purpose may, in fact, be quite impure for other uses. Absolute ethanol may contain traces of benzene, which makes it unsuitable for ultraviolet spectroscopy, or plasticizers which make it unsuitable for use in solvent extraction. 

Irrespective of the grade of material to be purified, it is essential that some criteria exist for assessing the degree of purity of the final product. The more common of these include  

Chemical tests for particular types of impurities, e.g. for peroxides in aliphatic ethers (with acidified KI), or for water in solvents (quantitatively by the Karl Fischer method, see Fieser and Fieser, Reagents for Organic Synthesis J. Wiley Sons, NY, Vol 1 pp. 353, 528, 1967, Library of Congress Catalog Card No 66-27894). 

Nuclear methods which include a variety of radioactive elements as in organic reagents, complexes or salts. 

A substance is usually taken to be of an acceptable purity when the measured property is unchanged by further treatment (especially if it agrees with a recorded value). In general, at least two different methods, such as recrystallisation and distillation, should be used in order to ensure maximum purity. Crystallisation may be repeated (from the same solvent or better from different solvents) until the substance has a constant melting point or absorption spectrum, and until it distils repeatedly within a narrow, specified temperature range. 

Emission and atomic absorption spectroscopy for detecting organic impurities arrd determining metal 

Chromatography, including paper, thin layer, hquid (high, medium and normal pressirre), flash and 

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The question of purity becomes of paramount importance when one studies the details of initiation by metal halides. A study of aluminium halide solutions in alkyl halide solvents shows that provided the impurity level is less than about 10"7 mol l 1, the halides ionise simply by binary disproportionation ... 

The question of purity of the circulating water is not at all critical. For example, the boron tolerance for a loss in k of 0.0001 is roughly 10 parts per million. This is easily attained by distillation, and if it were not for the possibility of oil contamination, power boiler condensate would be entirely satisfactory. However, it probably will prove desirable to have a water evaporation imit available for concentrating radioactive wastes anyhow, and this same unit may well be used for producing distilled water for the pile circulating system. 

The concept of a substance is something that needs to be learnt and goes hand in hand with particle theory. Without substances, particles have no identity. The distinction between pure samples and mixtures is also crucial there are no milk particles in the same sense as there are sugar (sucrose) particles. (Note that we should not talk about pure substances since the term is misleading. The question of purity relates to the sample not to the idea of a substance. For example, in this beaker is there only water Substances are just substances - there are not pure and impure substances.)... 

The question of purity arises regarding materials used to prepare standards. Two problems occur here the purity of the component of interest and the purity... 

High demands are placed on the substrate material of disk-shaped optical data storage devices regarding the optical, physical, chemical, mechanical, and thermal properties. In addition to these physical parameters, they have to meet special requirements regarding optical purity of the material, processing characteristics, and especially in mass production, economic characteristics (costs, processing). The question of recyclabiUty must also be tackled. 

In a chemical context the concept of purity is circumscribed by three questions which need to be answered before much progress can be made ... 

There are three aspects of the question of solvent purity that have to be considered the specification of the purity of the given solvent its further purification, if necessary and the testing of the actual purity of the original or purified solvent. 

Much attention is given in the literature to the question of cleanliness and the purity of starting materials. The importance of these precautions varies depending on the work to be undertaken but the use of doubly distilled de-ionised water as a subphase has become a standard precaution. The use of disposable surgical gloves when handling pieces of apparatus which will have contact with the subphase is also a wise precaution. 

Application of metal alkoxides in preparation of oxide materials assumes their high purity, which satisfies the requirements formodem electronic materials. Nevertheless, there are only few works that consider the question of purification of metal alkoxides and that give the characteristics of their purity [522]. Future studies of the syntheses of metal alkoxides should pay special attention to the problems of their purification. 

The question of the degree of perfection of the crystals should be mentioned. Crystals grown with a reasonable degree of care in respect to purity... 

For synthesizing tris-chelates (or bis-tridentate chelates) the ideal source material is RuC13 3 H20 simply because of its availability. Hypophosphite reduction in the presence of the ligand provides a fairly general, rapid synthetic technique. While there will always be questions of purity for compounds prepared by this route, it is a valuable method for the initial synthesis of a compound to determine general properties before exploring other synthetic routes. 

By 1965, the first massive manufacturing and distributing operation had come into being—Owsley s marvelous "tabs. Yet Stanley Owsley came from a background of interest in amphetamine, and some users soon raised questions as to whether he liked to add "speed to the product. Bruce Eisner, who has written much about the question of psychedelic purity, talked with Owsley s lab assistant, Tim Scully, and believes that speed was never added. 

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