Internal standards for

Radiochemical methods of analysis take advantage of the decay of radioactive isotopes. A direct measurement of the rate at which a radioactive isotope decays may be used to determine its concentration in a sample. For analytes that are not naturally radioactive, neutron activation often can be used to induce radioactivity. Isotope dilution, in which a radioactively labeled form of an analyte is spiked into the sample, can be used as an internal standard for quantitative work. 

Preliminary report on "Collaborative Study on the Proposed International Standard for Somatropin," National Institute for Biological Standards and Control, London, Dec. 21, 1992. 

Quantitative mass spectrometry, also used for pharmaceutical appHcations, involves the use of isotopicaHy labeled internal standards for method calibration and the calculation of percent recoveries (9). Maximum sensitivity is obtained when the mass spectrometer is set to monitor only a few ions, which are characteristic of the target compounds to be quantified, a procedure known as the selected ion monitoring mode (sim). When chlorinated species are to be detected, then two ions from the isotopic envelope can be monitored, and confirmation of the target compound can be based not only on the gc retention time and the mass, but on the ratio of the two ion abundances being close to the theoretically expected value. The spectrometer cycles through the ions in the shortest possible time. This avoids compromising the chromatographic resolution of the gc, because even after extraction the sample contains many compounds in addition to the analyte. To increase sensitivity, some methods use sample concentration techniques. 

Production of carbon electrodes is a capital-intensive business. Two suppHers dominate the prebaked market. Carbon paste producers are more numerous and tend to serve local markets. There is no international standard for the threaded joints on carbon electrodes. Manufacturers of straight pin carbon electrodes have followed the physical specifications adopted for graphite electrodes (37). Unified standards do not exist for pinless joints resulting in limited interchangeability among brands. Electrode diameters are offered in both English and metric sizes with no restrictions on new or unique diameters. 

This section covers only the tests that are essential on a completed motor, irrespective of the manufacturing procedure and stage quality checks. If ISO 9000 guidelines are assimilated, practised and enforced by a manufacturer so that a customer s trust is obtained, a final pre-despatch inspection by the customer may not be necessary. The customer, having gained confidence in the practices and Quality Assurance Systems of the manufacturer, may issue an authorization to the manufacturer to despatch the material under their own inspection certificate, rather than an inspection by the customer. We discuss below the test requirements procedure and the acceptance norms prescribed by various national and international standards for such machines and adopted by various manufacturers. 

In Raman spectroscopy the intensity of scattered radiation depends not only on the polarizability and concentration of the analyte molecules, but also on the optical properties of the sample and the adjustment of the instrument. Absolute Raman intensities are not, therefore, inherently a very accurate measure of concentration. These intensities are, of course, useful for quantification under well-defined experimental conditions and for well characterized samples otherwise relative intensities should be used instead. Raman bands of the major component, the solvent, or another component of known concentration can be used as internal standards. For isotropic phases, intensity ratios of Raman bands of the analyte and the reference compound depend linearly on the concentration ratio over a wide concentration range and are, therefore, very well-suited for quantification. Changes of temperature and the refractive index of the sample can, however, influence Raman intensities, and the band positions can be shifted by different solvation at higher concentrations or... 

EC Directive concerning the enforcement of international standards for ship safety, pollution prevention... 

TABLE 6.2 Developments of International Standards for the Ergonomics of the Thermal Environment... 

The procedures and requirements for rhe type and commissioning tests are covered in narional and international standards—for example, for laboratory fume cupboards, welding fumes, and kirchen hoods. 

The materials which are currently specified in the National and International Standards for use as implants together with their eissociated mechanical properties are shown in Table 2.23. 

IEC 86-1 International Standard for Primary Batteries. Nickel-Cadmium or Nickel-Metal Hydride Chargers, 1986. 

CAMPUS uses a uniform database structure and uniform interface for all participating suppliers, with frequent updates of the property data. It allows preselection or screening of materials, suitable for specific applications, from a worldwide range of commercial plastics, while continuously being developed further with respect to its properties base. CAMPUS is based on two international standards for comparable data, that use meaningful properties based on unambiguous selection of specimen types... 

Before this problem is considered further, let us sketch the history of internal standards for x-ray emission spectrography. They appear in... 

Fig. 7—8. Calibration curve for the determination of tungsten in solution with bromide as an internal standard, for two different counter tubes. Squares = krypton counted total count, 10(16,384) circles = argon counter total count, 5(16,384). (Fagel, Liebhafsky, and Zemany, Anal. Chem., 30, 1918.)...

We also expect our business partners -paper mills, printers, packaging manufacturers, etc. - to commit themselves to using materials and production processes that do not harm the environment. The paper in this book is made from low- or no-chlorine pulp and is acid free, in conformance with international standards for paper permanency. 

This method requires about 40 g of tobacco which are extracted with ethyl acetate in the presence of ascorbic acid. A trace amount of C-NDELA is added as an internal standard for quantitative analytical work. The filtered extract is concentrated and NDELA is enriched by column chromatography of the concentrate on silica gel. The residues of fractions with p-activity are pooled and redissolved in acetonitrile. Initially, we attempted to separate NDELA on a 3% OV-225 Chromosorb W HP column at 210 C using a GC-TEA system with direct interface similar to the technique developed by Edwards a. for the analysis of NDELA in urine (18). We found this method satisfactory for reference compounds however, it was not useful for an optimal separation of NDELA from the crude concentrate of the tobacco extract (Figure 4). Therefore, we silylated the crude concentrate with BSTFA and an aliquot was analyzed by GC-TEA with direct interface. The chromatographic conditions were 6 ft glass column filled with 3% OV-... 

International standards for selected chemical, microbiology and other parameters. 

When [ H]-labeled precursors are employed the resulting compounds can be used as internal standards for analysis, especially by utilization of mass spectrometric methods. Appropriate deuterated standards are shown in Fig. 7. The introduction of deuterium into the A9-THC precursors can be done with Grignard reagents such as C[ H3]MgI or reducing substances such as LiAl[ H4]. The general procedures for the synthesis with these [ Hj-labeled precursors are the same as described above for the unlabeled compounds [76,78]. 

In both the GC/MS and the LC-FL analyses selected perdeuterated PAHs were added to the samples prior to extraction for use as internal standards for quantification. 

Kline WF, Wise SA, and May WE (1985) The apphcation of perdeuterated polycydic aromatic hydrocarbons (PAH) as internal standards for the liquid chromatc aphic determination of PAH in petroleum crude oil and other complex mixtures. J Liq Chromatogr 8 223-237. 

Poole S, Dawson P and Gaines RE (1997) Second international standard for endotoxin calibration in an international collaborative study. J. Endotoxin Res. 4 221-231. 

Butler OT, Howe AM (1999) Development of an international standard for the determination of metals and metalloids in workplace air using ICP-AES evaluation of sample dissolution procedures through an interlaboratory trial, f Environ Monit 1 23-32. 

White, J. W. and Winters, K. (1989). Honey protein as internal standard for stable carbon isotope ratio detection of adulteration of honey. J. Assoc. Ojfic. Anal. Chem. 72,907-911. 

HS-GC methods have equally been used for chromatographic analysis of residual volatile substances in PS [219]. In particular, various methods have been described for the determination of styrene monomer in PS by solution headspace analysis [204,220]. Residual styrene monomer in PS granules can be determined in about 100 min in DMF solution using n-butylbenzene as an internal standard for this monomer solid headspace sampling is considerably less suitable as over 20 h are required to reach equilibrium [204]. Shanks [221] has determined residual styrene and butadiene in polymers with an analytical sensitivity of 0.05 to 5 ppm by SHS analysis of polymer solutions. The method development for determination of residual styrene monomer in PS samples and of residual solvent (toluene) in a printed laminated plastic film by HS-GC was illustrated [207], Less volatile monomers such as styrene (b.p. 145 °C) and 2-ethylhexyl acrylate (b.p. 214 °C) may not be determined using headspace techniques with the same sensitivities realised for more volatile monomers. Steichen [216] has reported a 600-fold increase in headspace sensitivity for the analysis of residual 2-ethylhexyl acrylate by adding water to the solution in dimethylacetamide. 

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