Definitive methods

A definitive method for stmctural deterrnination is x-ray crystallography. Extensive x-ray crystal stmcture deterrninations have been done on a wide variety of steroids and these have been collected and Hsted (270). In addition, other analytical methods for steroid quantification or stmcture determination include, mass spectrometry (271), polarography, fluorimetry, radioimmunoassay (264), and various chromatographic techniques (272). 

In conclusion, it is apparent that the lack of definitive methods for assessment of free radicals in muscle and other tissues inhibits clear conclusions to be drawn concerning the relevance (or lack of relevance) of these substances in muscle pathology. In particular, the relevance of free radicals to the deficits in muscle function (fatigue and damage), which occur with exercise, is still unclear despite extensive study. This and other areas require much further examination. 

The term definitive method is applied to an analytical or measurement method that has a valid and well described theoretical foundation, is based on sound theoretical principles ( first principles ), and has been experimentally demonstrated to have negligible systematic errors and a high level of precision. While a technique may be conceptually definitive, a complete method based on such a technique must be properly applied and must be demonstrated to deserve such a status for each individual application. A definitive method is one in which all major significant parameters have been related by a direct chain of evidence to the base or derived SI units. The property in question is either directly measured in terms of base units of... 

Independence of analysts and analyses in one organization is a fundamental question. It is important to have, even for the most reliable methods, more than one analyst/laboratory involved to avoid possible analyst/laboratory-specific biases. Certification by a single laboratory, without confirmation by another laboratory or method is risky. Measurement by a single definitive method is usually performed by two or more analysts working independently to minimize possible biases. Frequently, an accurately characterized back-up method is employed to corroborate the data. Some agencies feel that a certification campaign should not be based on a single measirrement procedure and therefore do not normally certify values on the basis of a definitive method applied in one laboratory. 

Independent reference methods - one organization Two or more independent reference methods, each based on an entirely conceptually different principle of measurement, independent in theory and experimental procedure, applied in replicate, within a single organization, of the highest reputational quality, by two or more expert analysts, working independently. The methods used can, naturally, include definitive methods, and the results should be corroborated by a third or additional, independently different, accurately characterized, well established, thoroughly validated, definitive, reference, or other methods. 

An extremely wide variety of analytical methods are used by RM producers and developers in the certification of RMs for inorganic elemental content. These methods range from the classical, through current instrument based methods to highly specialized definitive methods. 

A limited number of pure substances are available from NIST, primarily clini-cally-relevant compounds such as cholesterol, urea, uric acid, creatinine, glucose, cortisol, tripalmitin, and bilirubin (NIST SRM website). These compounds are certified for purity (greater than 99 %) and are used as primary calibrants in definitive methods for these clinical analytes (see below). Several additional pure substances are available for specific applications such as microchemistry, i.e. elemental composition (acetanilide, anisic acid, cystine nicotinic acid, o-bromobenzoic acid, p-fluoro-benzoic acid, m-chlorobenzoic acid), polarimetric standards (sucrose and dextrose), acidimetric standard (benzoic acid and boric acid). Only three pure substance NIST RMs are available for environmental contaminants, namely the chlorinated pesticides, lindane, 4,4 -DDT, and 4,4 -DDE. 

Cohen A, Hertz HS, Mandel J, Paule RC, Schaffer R, Sniegoski LT, Sun T, Welch MJ, and White E V (1980) Total serum cholesterol by isotope dilution mass spectrometry A candidate definitive method. Chn Chem 26 854-860. 

Ellerbe P, Cohen A, Welch MJ, and White V E (1990) Determination of serum uric acid by isotope dilution mass spectrometry as a candidate definitive method. Anal. Chem 62 2173-2177. 

Ellerbe PM, Sniegoski LT, and Welch MJ (1995) Isotope dilution mass spectrometry as a candidate definitive method for determining total glycerides and triglycerides in serum. Clin Chem 41 397-404. 

Ellerbe, P, Meiselman S, Sniegoski LT, Welch MJ, and White E V (1989) Determination of serum cholesterol by a modification of the isotope dilution mass spectrometric definitive method. Anal Chem 61 1718-1723. 

SlEKMANN L (1979) Determination of steroid hormones by the use of isotope dilution mass spectrometry a definitive method in clinical chemistry. J Steroid Biochem 11 117-123. 

Current methods for DNA detection usually require enzymatic amplification of the target DNA sequence prior to analysis. For example, the PCR technique selectively increases the concentration of the target sequence relative to unrelated sequences. PCR methods, however, introduce ambiguities resulting from contamination by different DNA sequence. Therefore, a definitive method is required for the analysis of a single, original DNA sequence. To achieve this objective, the sensitivity and speed of the chemiluminescent enhancement techniques described in this chapter must be improved. 

The joined class has all the methods from the partial definitions. Methods are joined according to the rules for actions Only one method for each signature is allowed (within this class) and not even that if there is a pre/post spec attached to that signature in one of the other joinees. Pre/post specs can be inherited from superclasses. 

Isotope dilution analysis is the definitive method for the quantitative analysis of many compounds but is usually only carried out in specialist laboratories. 

Certification using one definitive method. This option is employed when a highly established, internationally accepted scientific primary method is available. The method must be shown to have negligible systematic errors and to provide sufficient measurement accuracy. An example of such a method is isotope dilution mass spectrometry. 

Technical Drawings—Dimensioning-General Principles, Definitions, Methods of Execution, and Special Indications Pipe Threads Where Pressure-Tight Joints are Not Made on the Threads—Part I Designation, Dimensions and Tolerances ... 

Biomedical parameters, such as LD50, are well defined, but they are derived from the studies of different populations and represent statistical probabilities of animals and people. These numbers often change from one study to another, when different populations are used and species can develop resistances after long exposure. There is also no definitive method to relate and scale-up animal parameters to human parameters, or to scale among people of different ages and states of health so, they are more indicative than authoritative. 

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