Characteristic concentration

The sensitivity of an atomic absorption line is often described by its characteristic concentration, which is the concentration of analyte giving an absorbance of 0.00436 (corresponding to a percent transmittance of 99%). Eor example. Table 10.11 shows a list of wavelengths and characteristic concentrations for copper. 

Many chemicals when added to water cause a freezing point depression, as shown in Table 1, and thus are termed antifreezes. The antifreeze properties of these chemicals vary widely as a function of their coUigative, or concentrative, properties. The reduction in freeze point depends both on the chemical itself and the concentration of the chemical in water. The freeze point depression increases as the antifreeze chemical is added to the water, until a characteristic concentration is achieved. Further addition of the antifreeze chemical to water will either result in insolubility or serve to increase the freezing point of the mixture, as illustrated in Figure 1. 

The effectiveness is known from experiment for important industrial catalysts and is correlated, in general, in terms of pore characteristics, concentrations, and specific rate equations. 

In highly diluted solutions the surfactants are monodispersed and are enriched by hydrophil-hydrophobe-oriented adsorption at the surface. If a certain concentration which is characteristic for each surfactant is exceeded, the surfactant molecules congregate to micelles. The inside of a micelle consists of hydrophobic groups whereas its surface consists of hydrophilic groups. Micelles are dynamic entities that are in equilibrium with their surrounded concentration. If the solution is diluted and remains under the characteristic concentration, micelles dissociate to single molecules. The concentration at which micelle formation starts is called critical micelle concentration (cmc). Its value is characteristic for each surfactant and depends on several parameters [189-191] ... 

For normalization of the value of the heat transfer enhancement, we used its magnitude at the maximum for each curve. The result of such normalization is shown in Fig. 2.59. In this figure, C is the solution concentration, Cq is the characteristic concentration, h is the heat transfer coefficient at given values of the solution concentration and the heat flux q, /zmax is the maximum value of the heat transfer coefficient at the same heat flux, and /zw is the heat transfer coefficient for pure water at the same heat flux q. Data from all the sources discussed reach the same value of 1.0 at the magnitude of relative surfactant concentration equal to 1.0. 

These experiments have revealed the possibility of the ignition of individual catalyst pellets within the bed. Such pellets can stay dry after the ignition due to the efficient progress of reaction despite the fact that they are surrounded by liquid filled pellets [Figure 5.4.4(a)], The images also reveal the presence of the beads with the characteristic concentric pattern of liquid distribution, similar to that observed earlier (Figure 5.4.2) for individual cylindrical pellets. 

The random displacement of fluid particles along the scalar gradient creates a diffusive flux proportional to the characteristic velocity and the characteristic concentration... 

Another characteristic concentration in Fig. 17 is point , which gives the solubility limit of the solvent in the unreacted precursor mixture. If the solvent concentration exceeds this solubility hmit, demixing occurs in the initial state. 

Although blue dyes usually appear to be blue-black in bulk, a blue colour is seen when they are viewed at the edge of a smoke cloud. This is related to the spectral characteristics, concentration and particle size of the dye. 

CROW does not substantially reduce contaminant levels in soils that do not contain free product. High levels of dissolved metals like iron can form suspended solids or promote bacteria growth that will foul the system by blocking injection wells and clogging machinery. Soil type, stratigraphy, contaminant characteristics/concentrations, and local hydrogeology/geology will... 

The natural way of analyzing this problem is to introduce the appropriate scales. They would come from the characteristic concentration c, the characteristic length Lr, the characteristic velocity Qr, the characteristic diffusivity Dr and the characteristic time Tr. The characteristic length Lr coincides in fact with the "observation distance". Setting... 

The limit of detection is a useful figure which takes into account the stability of the total instrumental system. It may vary from instrument to instrument and even from day to day as, for example, mains-borne noise varies. Thus, for atomic absorption techniques, spectroscopists often also talk about the characteristic concentration (often erroneously referred to as the sensitivity—erroneously as it is the reciprocal of the sensitivity) for 1% absorption, i.e. that concentration of the element which gives rise to 0.0044 absorbance nnits. This can easily be read off the calibration curve. The characteristic concentration is dependent on such factors as the atomization efficiency and flame system, and is independent of noise. Both this figure and the limit of detection give different, but useful, information about instrumental performance. 

Q. What information is given by the limit of detection, and how does this differ from that given by the characteristic concentration ... 

Characteristic concentration (pgml-i) Detection limit (pgml-i)... 

Characteristic concentrations and detection limits quoted were all measured at the most sensitive line. Hollow cathode lamps were used throughout together with an R446... 

These are the only type of interference that do not require the presence of analyte. For AAS the problem of spectral interference is not very severe, and line overlap interferences are negligible. This is because the resolution is provided by the lock and key effect. To give spectral interference the lines must not merely be within the bandpass of the monochromator, but actually overlap each other s spectral profile (i.e. be within 0.01 nm). West [Analyst 99, 886, (1974)] has reviewed all the reported (and a number of other) spectral interferences in AAS. Most of them concern lines which would never be used for a real analysis, and his conclusion is that the only real problem is in the analysis of copper heavily contaminated with europium The most commonly used copper resonance line is 324.754 nm (characteristic concentration 0.1 pg cm- ) and this is overlapped by the europium 324.753 nm line (characteristic concentration 75 pg cm- ). 

Find the characteristic concentration (i.e. the concentration corresponding to an absorbance of 0.0044) for nickel (in iron solution) using this instrumentation by (a) interpolation of the graph (b) calculation from the slope. 

Report the analytical figures of merit (i.e. limit of detection, linear range, characteristic concentration) for the magnesium calibration and compare with literature values. 

Fig. 13.7. Concentration changes in cyclins during the cell cycle. Cychns of types D, A, E, and B show characteristic concentration changes in the course of the cell cycle. The figure only depicts the course of concentration changes in the cell cycle, and does not indicate the relative cyclin concentrations.

In the cell cycle, the different cyclins show characteristic concentration changes in which temporally defined maxima in cyclin concentration are observed (see Fig. 13.7). The changes in cyclin concentration during the cell cycle are initiated by regulated new synthesis and targeted proteolysis. 

Polybrominated Diphenyl Ethers. PBDEs also accumulate in adipose tissue, serum, and breast milk of the general population due to their lipophilic characteristics. Concentrations of PBDEs in breast milk are useful, non-invasive markers of maternal body burdens and of in utero and lactational exposures, but body burden assessments are limited by a lack of time-trend data for PBDEs in tlie milk of U.S. populations (Hooper and McDonald 2000). Breast milk monitoring programs are needed to provide time-trend data and to verify findings that PBDE levels have been exponentially increasing in breast milk during the past 25 years (Noren and Meironyte 1998, 2000). Studies on the predictive value of levels of PBDEs in scrum and adipose tissue could provide useful infonnation for detection and monitoring of exposure. 

For constant parameters k, C,in, kj2, the solution of the nonlinear differential Equation 21-24 is given in Box 21.5. The steady-state, Cim results from the solution of a quadratic equation. It is controlled by the characteristic concentration... 

The relative size of the input concentration, Cin, and the characteristic concentration, C, determines how C depends on Cin. The two extreme situations are ... 

Consider first the single equation, Eq. (5) and ask what it might be used for. We could, for example, ask what the effect of comparing the behavior for various, but still constant, values of cin might be. In this case, the answer is obvious because, the equations being linear, c is proportional to cm. If we take Cin as the characteristic concentration, then... 

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