Purity index

Determination of the physical constants and the establishment of the purity of the compound. For a solid, the melting point is of great importance if recrystalhsation does not alter it, the compound may be regarded as pure. For a hquid, the boiling point is first determined if most of it distils over a narrow range (say, 1-2°), it is reasonably pure. (Constant boUing point mixtures, compare Section 1,4, are, however known.) The refractive index and the density, from which the molecular refractivity may be calculated, are also valuable constants for liquids. 

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. 

Viable glass fibers for optical communication are made from glass of an extremely high purity as well as a precise refractive index stmcture. The first fibers produced for this purpose in the 1960s attempted to improve on the quahty of traditional optical glasses, which at that time exhibited losses on the order of 1000 dB/km. To achieve optical transmission over sufficient distance to be competitive with existing systems, the optical losses had to be reduced to below 20 dB/km. It was realized that impurities such as transition-metal ion contamination in this glass must be reduced to unprecedented levels (see Fig. 

Table 4 lists the specifications set by Du Pont, the largest U.S. producer of DMF (4). Water in DMF is deterrnined either by Kad Fischer titration or by gas chromatography. The chromatographic method is more rehable at lower levels of water (<500 ppm) (4). DMF purity is deterrnined by gc. For specialized laboratory appHcations, conductivity measurements have been used as an indication of purity (27). DMF in water can be measured by refractive index, hydrolysis to DMA followed by titration of the Hberated amine, or, most conveniendy, by infrared analysis. A band at 1087 cm is used for the ir analysis. 

The light chlorophenols, normally have a purity greater than 98.5%, but they often reach over 99%, or even 99.5% with direct phenol chlorination. The APHA color test is always below 100. For 2,4,6-ttichlorophenol, the 2,4,5-trichlorophenol content constitutes an essential quaUty index and should be under 20 mg/kg. None of the light chlorophenols contain any polychlorodibenzoparadioxins or polychlorodibenzofurans. 

Enzymes are excellent catalysts for two reasons great specificity and high turnover rates. With but few exceptions, all reac tions in biological systems are catalyzed by enzymes, and each enzyme usually catalyzes only one reaction. For most of the important enzymes and other proteins, the amino-acid sequences and three-dimensional structures have been determined. When the molecular struc ture of an enzyme is known, a precise molecular weight could be used to state concentration in molar units. However, the amount is usually expressed in terms of catalytic activity because some of the enzyme may be denatured or otherwise inactive. An international unit (lU) of an enzyme is defined as the amount capable of producing one micromole of its reaction product in one minute under its optimal (or some defined) reaction conditions. Specific activity, the activity per unit mass, is an index of enzyme purity. 

With liquids, the refractive index at a specified temperature and wavelength is a sensitive test of purity. Note however that this is sensitive to dissolved gases such as O2, N2 or CO2. Under favourable conditions, freezing curve studies are sensitive to impurity levels of as little as 0.(X)1 moles per cent. Analogous fusion curves or heat capacity measurements can be up to ten times as sensitive as this. With these exceptions, most of the above methods are rather insensitive, especially if the impurities and the substances in which they occur are chemically similar. In some cases, even an impurity comprising many parts per million of a sample may escape detection. 

Refractive index The refractive index of the clear anodic film produced on aluminium of the highest purity in sulphuric acid is 1-59 in the as-formed condition, rising to 1-62 after sealing . 

Parathion (0,0-diethyl 0-p-nitrophenyl thiophosphate) is an ester of thiophosphoric acid with the empirical formula C10H14NO5PS. It is a high boiling deep-brown to yellow liquid, some samples of which possess a characteristic odor. Its boiling point has been calculated to be 375 0 C. or higher, at 760 mm. pressure its refractive index is n 5 1.15360 specific gravity is 1.26. The vapor pressure is 0.0006 mm. of mercury at 24° C. The technical grade has a purity of approximately 95%. 

Chemists are invited to submit for publication in Organic Syntheses procedures for the preparation of compounds which are of general interest or which illustrate useful synthetic methods. The procedures submitted should represent, as nearly as possible, optimum conditions for the preparations, and should have been checked carefully by the submitter. Full details of all steps in the procedure should be included, and the range of yields should be reported rather than the maximum yield obtainable. The melting point of each solid product should be given, and the boiling-point range and refractive index (at 25°) of each liquid product. The method of preparation or source of the reactants and the criteria for the purity of the products should be stated. 

Korany et al. [28] used Fourier descriptors for the spectrophotometric identification of miconazole and 11 different benzenoid compounds. Fourier descriptor values computed from spectrophotometric measurements were used to compute a purity index. The Fourier descriptors calculated for a set of absorbencies are independent of concentration and is sensitive to the presence of interferents. Such condition was proven by calculating the Fourier descriptor for pure and degraded benzylpenicillin. Absorbance data were measured and recorded for miconazole and for all the 11 compounds. The calculated Fourier descriptor value for these compounds showed significant discrimination between them. Moreover, the reproducibility of the Fourier descriptors was tested by measurement over several successive days and the relative standard deviation obtained was less than 2%. 

The refractive index will vary with the purity of the oleic acid. Oleic acid purified by low-temperature crystallization and by conversion into the oleic acid-urea complex (95.3% oleic, 0.7% linoleic) yielded a product with wf 1.4613. 

The checkers found that the refractive index of the pyrroline increases rapidly on exposure to air, impairing its usefulness as a criterion of purity. 

The computerized laboratory analytical data of heroin exhibits is used to calculate the price per milligram of pure heroin. The price-purity data can he used by statisticians as a market index—like Dow Jones—to determine trends and changes in the domestic heroin market. 

Although even lower WF can be achieved with, e.g., Yb (0 = 2.4 eV), the low reflectivity index of the latter makes it less suitable for OLED applications. The active metal Ca (0 = 2.60 eV) often has to be accompanied with other metals such as Al to increase the device lifetime. It is worth noting that the WF of the metals can be affected by their purity, their deposition method, and the surface structure, and the crystal orientation of the deposited films. 

Refractive index is a measure of the velocity of light in air divided by the velocity of light in the compound of interest. Accurate measurement of refractive indices requires careful temperature control. The refractive index is sensitive to the purity of the substance. 

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