Reference standards definitions

USP34-NF29 S1 <11> General Requirements/< 1 >USP Reference Standards—definition and applications... 

Provide clinical condition(s). Use reference standard definitions as.found mOMIM,. . . ... 

The appropriateness and essence of this distinction between absolute and relative configuration in this case may be illustrated by a hypothetical experiment. By definition, the determination of an absolute configuration involves a comparison with a fixed reference standard. Such a standard may be simulated by an enzyme that can discriminate between the isomers 16a and 16c, which differ in the configuration of the central atom. If the reacting isomer 16a is represented by (2/ ,3r,4S)-2,4-dihydroxy-3-((/ )-[2-2H]-propionoxy)glutaric acid, it can be predicted with confidence that the enzyme will also react with the enantiomer... 

The closeness or proximity of a measured value to the true value for a quantity being measured. Unless the magnitude of a quantity is specified by a formal SI definition, one typically uses reference standards to establish... 

These and other factors must b6 examined before a method or apparatus is condemned for lack of agreement with some other method or instrument. It is often simpler and more definitive to establish that an apparatus is properly working and calibrated than it is to use reference standards which are subject to the hazards listed above. Furthermore, the question must always arise regarding the merits of the technique and apparatus used to establish the value of the standard in the first instance. Experimental results obtained with a carefully calibrated apparatus are preferred to results which may agree with a presumed standard whose properties may change or which may have been incorrectly measured in another laboratory. 

There are two definitions of protein hydrophobicity average hydrophobicity and surface hydrophobicity. The average hydrophobicity was defined by Bigelow (1967) as the total hydrophobicity of all amino acid residues comprising a protein divided by the number of amino acids in the protein. There is no standard definition of surface (or effective) hydrophobicity except the concept that there must be hydrophobic regions on the molecular surface that play an effective role in protein function. Readers who are interested in a more detailed discussion are referred to Nakai and Li-Chan (1988). 

Although it is not really needed at this point, we introduce the concept of activity coefficients, which are very common for chemical engineers, but much less for theoretical and computational chemists. In the standard definition, the activity coefficients make reference to the pure liquid compound, i, at the same temperature and pressure. Hence, the activity coefficient yt of species i is defined by... 

For a value to be traceable it must be related to stated references. By definition and convention the stated references are taken to include SI [6] reference values (e.g., atomic mass values), reference materials (RMs), as well as primary, reference, and standard methods. It is sometimes stated that chemical measurements are traceable to the mole. This is an incomplete statement as chemical measurements are simultaneously traceable to a number of references, inter alia, the mole, kg, meter, etc. Whilst it is considered desirable to employ high level references, such as the SI, where feasible, this is not always necessary in terms of fit for purpose criteria. Neither is it possible to relate all types of analyte (fat, fiber, protein, pH, etc.) to the SI. The key issue is that the references should be stated and fit for purpose. 

If a statement of comparability at any confidence level needs to be made then other information is essential. The uncertainty of the results is needed [6], because only results accompanied by measurement uncertainty are comparable. To obtain consistent and useful measurement results, it is important that both a chain of comparisons to reference standards, and the uncertainties associated with these comparisons, are established. These principles lead directly to the definition of traceability in the International Vocabulary of Basic and General Terms in Metrology (VIM) as Property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties [4]. 

The definition makes no mention of attributes of the measurand s material matrix or of that of the stated reference, although the ability to compare measu-rands does not only depend on the relevant quantity and its values, but also on other attributes of the sample and reference standard. The associated components of uncertainties must be kept in mind. 

References to definitive studies on phenanthrolines are given in Summers review <78AHC(22)l>. In many of the publications cited in this chapter, IR spectral observations are given as supporting evidence for structures by comparison with standard reference data. 

The components of J referred to the new coordinate system then have completely standard definitions ... 

TABLE 2. Flavor and Odor Terms, Definitions, and Reference Standards Used in the Evaluation of Fats, Oils, and Oil-Containing Foods. 

Terms used to describe reference standards differ among industries and also among companies in the pharmaceutical industry. The following definitions, consistent with literature references,2-13 will be used throughout... 

Reference standards are properly categorized for their intended use. A definition section that clearly links the type of reference standard to its intended use is critical. 

Phase-solubility analysis17 (sometimes referred to as phase equilibrium purification) is the quantitative determination of the purity of a substance through the application of precise solubility measurements. At a given temperature, a definite amount of a pure substance is soluble in a definite quantity of solvent. The resulting solution is saturated with respect to the particular substance, but the solution remains unsaturated with respect to other substances even though such substances may be closely related in chemical structure and physical properties to the particular substance being tested. There are examples of the use of this technique in HPLC methods development18 and in the characterization of reference standards,19 but the... 

Fig. 1 Terminology reference material (RM) vs. certified reference material (CRM). Inconsistent terminology is a fertile base for various interpretations of definitions definitions given in Table 1 can be interpreted as given in case 1 (CRMs being a part of a family named RM) or as given in case 2 (several different types of RM, one of them being CRM). Intended use of reference standard depends on accepted interpretation of definitions...

Definition of and rationale for the units, cutoffs and/or categories of the results of the index tests and the reference standard. ... 

The preliminary draft guidelines for the establishment of secondary reference substances were presented to the Committee. The Committee endorsed the general approach and agreed that a definition of a pharmacopoeial reference standard should be included before the text was circulated for comment. 

This leads to unique definition of the stability constants of monodentate surface complexes involved in the specific adsorption of cations. Thus, reaction (5.65) rather than reactions (5.66)-(5.68) should be chosen as a standard definition, according to the above standards. The exact definition of the stability constant of the =TiOCd species in the present example depends on the electrostatic position of Cd in the surface complex. It should be also emphasized that even with fixed electrostatic position of Cd, the numerical value of the equilibrium constant of reaction (5.65) depends on the choice of the model of primary surface charging. The details on the models of primary surface charging are not given in the tables in Chapter 4, and the reader is referred to the original publications. 

When the enzyme is itself a pure chemical entity and the only catalytic agent present, which is exceptional, conditions are fulfilled for an unambiguous definition of units of activity, which is proportional to the reaction rate obtained. Furthermore it is essential to have a detailed knowledge of the biochemical transformation that is obtained and its reaction scheme. When the enzyme is not 100% pure, in order to define activity, a reference standard must be used with the same assay method and substrate the activity of the unknown enzyme preparation is then expressed in terms of the reference standard. 

The tendency for a specific substance to lose or gain electrons is called its redox or reduction potential. The redox potential of a conjugate redox pair is measured in an electrochemical cell against a reference standard, usually a standard hydrogen electrode. The redox potential of the standard hydrogen electrode is 0.0 V at 1 atm, by definition. Substances with a more negative... 

The ultimate goal of an assay or an analytical procedure is to measure accurately a quantity or a concentration of an analyte, or to measure a specific activity, as in some assays for biomarkers. However, many activity assays, such as cell-based and enzyme activity assays, may not be very sensitive, may lack precision, and/or do not include the use of definitive reference standards. Assays based on measurements of physicochemical (such as chromatographic methods) or biochemical (such as ligand-binding assays) attributes of the analyte assume that these quantifiable characteristics are reflective of the quantities, concentration, or biological activity of the analyte. For the purpose of bioanalytical method validation, we will follow the recently proposed classifications for assay data by Lee et al. [4,5]. These classifications, as summarized below, provide a clear distinction with respect to analytical validation practices and requirements. 

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