The General. Selective, and Specific

The general, selective and specific formation of complexes by metallic cations. G. Schwarzenbaeh, Adv. Inorg. Chem. Radiochem., 1961, 3, 257-285 (70). 

The General, Selective, and Specific Formation of Complexes by Metallic Cations... 

The terms selectivity and specificity are often interchangeably used. The term specificity generally refers to a method that produces a response for a single analyte only, while the term selective refers to a method that provides responses for a number of chemical entities that may or may not be distinguished from each other. Because there are very few methods that respond to only one analyte, the term selectivity is usually more appropriate. The USP defines selectivity of an analytical method as its ability to accurately measure an analyte in the presence of interferences, such as synthetic precursors, excipients, enantiomers, and known (or likely) degradation products that may be expected to be present in the sample matrix. 

These polar functional groups are mostly reduced to the corresponding alcohols with hydride reagents (A. Hajos, 1966, 1979). The general selectivities are indicated in table 1 (p. 97f.) and a few specific examples will be given here. 

Performance of the power-recovery unit operating with a makeup driver (Fig. 29-56) is shown in Fig. 29-57 specific percentage values are shown, but the general characteristics and curwe shapes are typical. It should be noted that the flow scheme, the selection of... 

In general, the strengths of the ELISA are its selectivity and specificity, whereas its weaknesses are related to precision of measurement. Each assay varies — depending on the antibody, enzyme, enzyme conjugate, and measurement, as well as on assay format. Each should be validated so that its unique performance characteristics are known. 

The most sensitive and specific detector is ED, but the insolubility of the electrolytes in NP eluents preclude its wide application. A FED is generally preferred due to its higher selectivity and specificity than a UV method, but the latter may be preferred in simultaneous analysis of other lipophilic compounds such as TAGs, sterols, and vitamins A, D, and K [448,482,483]. MS and tandem MS have been recently introduced as detector for vitamin E. 

Selectivity is often referred to as the specificity of an analytical method and is a measure of the discriminating ability of the technique. The general requirement for specificity is that the method should be capable of unambiguously determining the compounds of interest in the presence of impurities, degradation products and other sample matrix components. A specificity study often involves accelerated degradation studies to ensure all degradation products will not interfere and the collection of likely process impurities. Often a placebo sample is assayed to check for interference fi om the sample matrix. 

Selectivity is the ability of the bioanalytical method to measure and differentiate the analytes in the presence of components that may be expected to be present. Specificity is the ability to assess unequivocally the analyte in the presence of components that may be expected to be present. In general, analytical methods are selective, and only in same cases also specific (e.g., an LC-MS/MS bioanalytical method is highly selective but not always also specific because it could be possible to find in the complex biological matrix an interference with the same retention time, molecular weight, and main fragment of the analyte of interest). Even if the 2000 Washington conference focuses only on selectivity, it is up to bioanalytical laboratories to differentiate in their documentation between selectivity and specificity or consider them equivalent and use them interchangeably. 

The experimental evidence favors the conclusion that in addition of nucleophiles to carbonyl groups the observed catalysis is true general acid catalysis. Table 8.2 presents selected data a decreases with increasing nucleophilicity of the addend. More specific techniques applicable to particular reactions lead to the same conclusion.27 For hydration, Mechanism I of Scheme 5, with true general acid catalysis in the forward direction and specific acid plus general base catalysis in the reverse direction, thus appears to be the most reasonable one. 

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