Assay of materials

A knowledge of the half-life is required for any application in which quantitative assay of material for radionuclide content is desired. In fission-reactor research and technology, for example, accurate half-life... 

Electron microscopy Visualization of structures down to atomic details, usually in UHV, but environmental versions available Site concentrations difficult to establish, antilysis refers to small assay of material under study (support by averaging technique desirable) in situ (limited)... 

The quahty of formamide suppHed by BASE is certified as having a minimum assay of 99.5%. The principal impurities in the material are ammonium formate, methanol, water, and traces of iron. The quaUty of formamide supphed by BASE is certified to meet the specifications given in Table 3. 

In addition to encompassing all of the unit operations in the plant, the plant flow sheets may also include materials handling operations associated with the transport and storage of materials in and around the mill. Typically, flow sheets provide quantitative information regarding water and slurry flows, toimages, and assays. 

The cmde product formed from the alkylation of phenol with isoamylene contains principally 2-/ r2 -amylphenol, 4-/ r2 -amylphenol, and 2,4-di-/ r2 -amylphenol. 4-/ r2 Amylphenol is purified to its typical assay of 99+% by fractional distillation. 4-/ r2 -Amylphenol [80-46-6] is commercially available as a soHd, flaked material packaged ia paper or plastic bags (25 kg net weight) or as a molten material ia tank wagon or railcar quantities. 

In the United States, aluminum sulfate is usually produced by the reaction of bauxite or clay (qv) with sulfuric acid (see Sulfuric acid and sulfur trioxide). Bauxite is imported and more expensive than local clay, generally kaolin, which is more often used. Clay is first roasted to remove organics and break down the crystalline stmcture in order to make it more reactive. This is an energy intensive process. The purity of the starting clay or bauxite ore, especially the iron and potassium contents, are reflected in the assay of the final product. Thus the selection of the raw material is governed by the overall economics of producing a satisfying product. 

Preferably, high pressure Hquid chromatography (hplc) is used to separate the active pre- and cis-isomers of vitamin D from other isomers and allows their analysis by comparison with the chromatograph of a sample of pure reference i j -vitainin D, which is equiUbrated to a mixture of pre- and cis-isomers (82,84,85). This method is more sensitive and provides information on isomer distribution as well as the active pre- and cis-isomer content of a vitamin D sample. It is appHcable to most forms of vitamin D, including the more dilute formulations, ie, multivitamin preparations containing at least 1 lU/g (AOAC Methods 979.24 980.26 981.17 982.29 985.27) (82). The practical problem of isolation of the vitamin material from interfering and extraneous components is the limiting factor in the assay of low level formulations. 

The use of mutant 34486 of Neurospora crassa for the microbiological assay of ch oline has been described (8). A physiological method has also been used in which the ch oline is extracted after hydrolysis from a sample of biological material and acetylated. The acetylcholine is then assayed by a kymographic procedure, in which its effect in causing contraction of a piece of isolated rabbit intestine is measured (33). 

The crude ketal from the Birch reduction is dissolved in a mixture of 700 ml ethyl acetate, 1260 ml absolute ethanol and 31.5 ml water. To this solution is added 198 ml of 0.01 Mp-toluenesulfonic acid in absolute ethanol. (Methanol cannot be substituted for the ethanol nor can denatured ethanol containing methanol be used. In the presence of methanol, the diethyl ketal forms the mixed methyl ethyl ketal at C-17 and this mixed ketal hydrolyzes at a much slower rate than does the diethyl ketal.) The mixture is stirred at room temperature under nitrogen for 10 min and 56 ml of 10% potassium bicarbonate solution is added to neutralize the toluenesulfonic acid. The organic solvents are removed in a rotary vacuum evaporator and water is added as the organic solvents distill. When all of the organic solvents have been distilled, the granular precipitate of 1,4-dihydroestrone 3- methyl ether is collected on a filter and washed well with cold water. The solid is sucked dry and is dissolved in 800 ml of methyl ethyl ketone. To this solution is added 1600 ml of 1 1 methanol-water mixture and the resulting mixture is cooled in an ice bath for 1 hr. The solid is collected, rinsed with cold methanol-water (1 1), air-dried, and finally dried in a vacuum oven at 60° yield, 71.5 g (81 % based on estrone methyl ether actually carried into the Birch reduction as the ketal) mp 139-141°, reported mp 141-141.5°. The material has an enol ether assay of 99%, a residual aromatics content of 0.6% and a 19-norandrost-5(10)-ene-3,17-dione content of 0.5% (from hydrolysis of the 3-enol ether). It contains less than 0.1 % of 17-ol and only a trace of ketal formed by addition of ethanol to the 3-enol ether. 

The basic elements and considerations for assay development, validation, and specification assignment are reviewed briefly. Assay development produces a method that requires validation for the analysis and release of materials (bulk or formulated finished product) for use in clinical development. The cumulative analysis of materials and stability considerations is then used to established specifications for internal and regulatory submission. 

In the development of a SE-HPLC method the variables that may be manipulated and optimized are the column (matrix type, particle and pore size, and physical dimension), buffer system (type and ionic strength), pH, and solubility additives (e.g., organic solvents, detergents). Once a column and mobile phase system have been selected the system parameters of protein load (amount of material and volume) and flow rate should also be optimized. A beneficial approach to the development of a SE-HPLC method is to optimize the multiple variables by the use of statistical experimental design. Also, information about the physical and chemical properties such as pH or ionic strength, solubility, and especially conditions that promote aggregation can be applied to the development of a SE-HPLC assay. Typical problems encountered during the development of a SE-HPLC assay are protein insolubility and column stationary phase... 

In more recent times chemically defined basal media have been elaborated, on which the growth of various lactic acid bacteria is luxuriant and acid production is near-optimal. The proportions of the nutrients in the basal media have been determined which induce maximum sensitivity of the organisms for the test substance and minimize the stimulatory or inhibitory action of other nutrilites introduced with the test sample. Assay conditions have been provided which permit the attainment of satisfactory precision and accuracy in the determination of amino acids. Experimental techniques have been provided which facilitate the microbiological determination of amino acids. On the whole, microbiological procedures now available for the determination of all the amino acids except hydroxy-proline are convenient, reasonably accurate, and applicable to the assay of purified proteins, food, blood, urine, plant products, and other types of biological materials. On the other hand, it is improbable that any microbiological procedure approaches perfection and it is to be expected that old methods will be improved and new ones proposed by the many investigators interested in this problem. 

Assay of luciferin and luciferase. To assay luciferin, 1 ml of 5 mM phosphate buffer, pH 6.8, containing crude luciferase (which contains the purple protein) is added to 5—l0 xl of an ethanolic solution of luciferin, and the total light emitted is measured. To assay the activity of luciferase in crude material, 1 ml of 5 mM phosphate buffer, pH 6.8, containing a standard amount of luciferin is added to 5-10 xl of the sample, and the intensity of emitted light is measured. To assay purified luciferase, 1 ml of 5 mM phosphate buffer, pH 6.8, containing a standard amount of luciferin and a standard amount of purple protein is added to 5-10 xl of a sample, and the light intensity is measured (Shimomura and Johnson, 1968b,c). 

There is one important simple case in which direct x-ray emission spectrography is useless for the determination of major constituents. Consider the series Fe, FeO, Fe304, Fd203. The assay of these materials for iron by wet methods is, of course, routine and highly precise. In x-ray emission spectrography, the four substances will all give virtually... 

Non-specific absolute assay methods, e.g. volumetric titration, can be applied to avoid the establishment of a reference substance. This is only appropriate, however, when the monograph describes a separation test for related substances. This approach is certainly valid for the determination of the content of pharmaceutical raw materials but less acceptable for the assay of content of pharmaceutical preparations where the employment of specific assay methods is recommended (ICH Guideline 1994) to take account of decomposition of the active ingredient during the shelf life of the product and to avoid possible interference from excipients. 

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