Standards for Measurement

Careful and accurate measurements for each ingredient are essential when baking or cooking as well as in the chemistry laboratory. 

Examples show you problem-solving techniques in a step-by-step form. Study each one and then try the Practice Exercises. 

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There is no gold standard for measuring the content of the triacylglycerol store, since adipose tissue is distributed in many different depots (see Appendix 2.4 for some of the methods that are available). 

In 1960 the International Committee of Weights and Measures selected radioactive cesium-137 (with a half-life of about 33 years) as the standard for measuring time. They equated the second with the radiation emitted by a Cs-137 atom that is excited by a small energy source. Thus, the second is now defined as 9,192,631,770 vibrations of the radiation emitted by an atom of Cs-137. There are about 200 atomic clocks around the world that collaborate their efforts to maintain this extremely accurate clock that never needs winding or batteries. 

Poly(methyl methacrylate) ((PMMA) Elvacite) is a high molecular weight polymer available from duPont which was used as a standard for measuring sensitivities. 

For many years the international standard for measuring dimensions was ISO 4648 but recently its content has been incorporated into the general standard for preparing and conditioning test pieces for physical test methods, ISO 23 5 297. This has four methods dealing with dimensions less than 30 mm, dimensions over 30 mm, over 100 mm and non-contact procedures respectively. 

The international standard for measurement of resistivity of rubbers is ISO 185317 which details one procedure only, the potentiometric or four electrode method. The principle of the method is shown in Figure 13.2 the strip test piece has metal current electrodes clamped at each end and is... 

The stable free radicals in coal can adversely affect the 13C signal intensity. However, the quantitative reliability of the method can be greatly improved by prior treatment of coal with chemicals such as samarium(II) iodide (Stock et al., 1988) to selectively reduce the organic free radicals. Thus, this potential error that has influenced the quantitative aspects of the method can be reduced by the use of a novel pretreatment technique as well as an appropriate standard for measurement of chemical shifts. 

A system known as SI from the French name, Systeme International d Unites, has been adopted by many international bodies, including the International Union of Pure and Applied Chemistry, to institute a standard for measurements. In SI, the reference units for length, mass, and time are meter, kilogram, and second, with the symbols m, kg, and s, respectively. 

Javorszky, E., G. Erdoedy, and K. Torkos. 2006. The choice of internal standards for measuring volatile pollutants in water. Chromatographia 63 S55-S60. 

When properly engineered and with [H30(aq)] at unity activity and Pm at unit fugacity, this electrode system is the thermodynamic reference standard for measurements of electrochemical potentials, and is referred to as the normal hydrogen electrode (NHE), which is alternatively called standard hydrogen electrode (SHE) ... 

IMO MSC.41(64) Interim standard for measuring smoke and toxic products of combustion, International Maritime Organisation. 

The metric system is the standard for measurements of all branches of science. 

TIR-based techniques that use fluorescence transduction (TIRF) have been used for the majority of the applications discussed above. These platforms, while not currently the gold standard for measurement of many target analytes, do offer advantages over current technologies, such as cell culture, chromatography, and the enzyme-linked immunosorbant assay (ELISA). Advantages include the ability to perform faster, more sensitive, multiple analyte, and real-time measurements. 

Special Features The first global standard for measurement and reporting of social and ethical performance. A A 1,000 is a widely used standard for corporate social reporting in the UK. 

Different score systems have been developed to estimate, following a Q-wave infarction, its size and ventricular function (Hinohara et al., 1984 Pahlm et al., 1998 Pahneri et al., 1982 Selvester, Wagner and Hindman, 1985 Wagner and Hino-hara, 1984). However, currently CE-CMR is the gold standard for measurement and characterisation of infarcted area (see Quantification of the infarcted area ). 

A new set of standards for measuring fluorescence quantum yields has been proposed." The reference compoimds are photostable and their emission yields are relatively insensitive to the presence of dissolved oxygen. Procedures for correcting spectral data for changes in refractive index have been proposed for both solutions and suspensions." Likewise, problems arising from inner-filter effects have been reconsidered in light of corrections to Stern-Volmer constants " and improved cell design." " ... 

The H and C chemical shifts reported in this review are referenced to tetramethylsUane (TMS) as the internal standard on the 8 scale (ppm). Liquid NH, has been used as the external standard for the " N chemical shifts, with the following values employed to correct the chemical shifts originally reported relative to other commonly used standards liquid NH3 (0.0 ppm), 1 M urea in DMSO (77.0 ppm), 1 M HNO, in H2O (377.3), liquid MeNO, (381.7 ppm). Liquid nitromethane and 1 M urea in DMSO-Jg are frequently used as secondary external standards for measurements in coaxial systems or in separate experiments. A more detailed discussion can be found in recently published review articles on nitrogen NMR spectroscopy. " 2 ... 

The Beers criteria were updated recently/ At present, it is not clear what is the best way to measure inappropriate prescribing. Global measures for detecting polypharmacy or unnecessary drug use and underuse of essential medications are needed, as well as additional studies examining drug-disease interactions and other health outcomes. Moreover, we recommend further studies of the predictive validity of evidence-based standards for measuring inappropriate medications in the elderly. 

There appears to be no pharmaceutical industry standard for measuring the efficiency of a packaging line. Line efficiency has been defined as the ratio of output to input, but a better measure is the ratio of the actual operating time (the actual time producing acceptable product) divided by the available time (when there is work available for the line) expressed as a percentage. 

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