Selectivity/sensitivity, defined

When a topically applied compound induces a biological response following skin absorption, the quantitation of that response may provide a basis for assessing skin absorption. Indeed, such physiological or pharmacological responses have been employed as endpoints in assessing skin absorption in vivo, and perhaps the most successful example is the vasoconstrictor response to topical corticosteroids. However, while these pharmacodynamic endpoints may be very sensitive and selective for defined classes of compounds, it should be noted that the parameter measured is the product of both the quantity and the potency of the compound under investigation and may not necessarily reflect the extent of skin absorption, cutaneous metabolism, or disposition. 

From the results shown in Table 16.1, three parameters may be calculated selectivity, sensitivity and efficiency, as defined in Eqs. 16.31-16.33. In this example, all three parameters are equal to 100%. 

Often the purpose of collaborative trials is to evaluate a new analytical method operated in several laboratories. According to lUPAC a collaborative study is an interlaboratory study in which each laboratory uses the defined method of analysis to analyze identical portions of homogeneous materials to assess the performance characteristics obtained for that method of analysis, e.g., specificity, selectivity, sensitivity, range, limit of quantification, limit of detection, linearity, accuracy, and precision. Only methods giving small interlaboratory variations will be adopted for use as a standard method. Attention has to be paid to the design of collaborative studies for... 

Element sensitivity depends on the emission intensity at the measured wavelength. Each element has a number of possible wavelengths for determination and the best must be chosen also taking into account selectivity. Different emission lines have different sensitivities in diflfer-ent plasmas. Sensitivity, defined by the slope of the response curve, is less often used in C-AED than detection limit , expressed as absolute values of element mass (in a resolved peak) or in mass flow rate units. Detection limits for different elements vary by two or three orders of magnitude this affects inter-element selectivity if spectral overlap is present. 

Multicomponent analysis by non-selective methods is based on the measurement of total analytical signal (AS) of mixture of components at several intensive parameters and on the constmction of combined equations and the solving of it. The difference of partial sensitivity of components determined in common defines uncertainty. 

The selection of the cure system in these applications is directed by constraints such as location of the adhesive in terms of confined space, speed and depth of cure, etc. The volumes of silicones typically applied are relatively small. In general, the uncured adhesive needs to be dispensed in a well-defined and limited area, and needs to stay in place without flowing during cure. No by-products of the cure reaction are acceptable as they may contaminate other sensitive areas of the devices. These constraints often direct the choice to the platinum-catalyzed hydrosilylation cure system that is relatively expensive. 

Solid-surface luminescence analysis is a useful approach for organic trace analysis because of its simplicity, sensitivity, and selectivity. It will continue to be used in environmental analysis and other areas not only for the reasons mentioned above but also because it is readily adaptable to field work. By developing a fundamental understanding of the interactions responsible for strong RTF and RTF signals, the advantages and disadvantages of the luminescence approach will be more specifically defined in the future. 

Solid-Fluid Equilibria The solubility of the solid is very sensitive to pressure and temperature in compressible regions, where the solvent s density and solubility parameter are highly variable. In contrast, plots of the log of the solubility versus density at constant temperature often exhibit fairly simple linear behavior (Fig. 20-19). To understand the role of solute-solvent interactions on sofubilities and selectivities, it is instructive to define an enhancement factor E as the actual solubihty divided by the solubility in an ideal gas, so that E = ysP/Pf, where P is the vapor pressure. The solubilities in CO2 are governed primarily by vapor pressures, a property of the solid... 

The sensitivity achieved (LOD) is not normally presented. It is recognized that different laboratories determine dissimilar values for this parameter and even within a laboratory the repeatability of the LOD is low. Most often, the lowest validated concentration gives an impression about the lowest levels that can be analyzed generally with acceptable results. A measure of selectivity is the intensity of blank results. This intensity is discussed by the participants of inter-laboratory validation studies. However, results are not reported and limits are not defined by CEN TC 275. The results of method validations of the several multi-residue/multi-matrix methods are not reported in the same way, but newer methods with limited scope generate analogous tables with validation results (as an example, see Table 7). 

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