Response saturates

The first example employed an immobilization of GOx and a pH-sensitive dye (l-hydroxypyrene-3,6,8-trisulfonate, HPTS) on the tip of an optical fiber.44 As the local pH was reduced by gluconic acid production, measurable changes in fluorescence were observed. Using flow-through measurements with buffer solutions of various strengths, the optrode response time was determined to be 8-12 min, with a detection limit of 1.8-36 mg/dL glucose and response saturation at 36-54 mg/dL. 

Detector saturation can effect both quantitative and qualitative data analysis, and each of these effects should be appreciated. The effect on sample quanti-tation is intuitive, where for instance a twofold increase in sample concentration produces a less than twofold increase in response. This will cause a flattening of calibration curves at higher concentrations. For API techniques, source saturation (or ion suppression) is another source of response saturation independent of detector saturation. Detector saturation can also effect qualitative measurements such as mass accuracy and isotope ratio calculations. In the former, when a mass spectral peak that has some finite resolution stalls to saturate the detector the peak-top calculations that provide the m/ measurement of the peak will become ambiguous. Likewise, it is possible that as one isotope of an ion starts to saturate the detector, adjacent isotopes in the distribution will still provide a linear response. The result of this is that incorrect isotope ratios will be obtained. Changes in relative isotope ratios of individual spectra across a chromatographic peak is an indicator of possible detector saturation. 

Shape of dose response (saturation, Dose response assay with... 

For small particles, and in many other cases, one will use fluorescence instead of transmission. However, saturation effects such as we saw for transmission mode also occur in fluorescence as well (Troger et al. 1992 Castaner and Prieto 1997). The classic case here is that of a thick piece of pure metal such as Cu. In this material, the ratio of the resonant to non-resonant absorption is about 85 15. This means that for every 100 incident photons, 85 of them create -holes and thus could stimulate fluorescence. Now, suppose the resonant absorption goes up by 10% due to EXAFS. Now the ratio is 93.5 15, or about 86.1 13.9. Thus, the resonant process accounts for 86.1% of the total, which means the fluorescence intensity only goes up by 1.3% instead of 10%. This example shows that, again, the response saturates as a function of the absorption one wants to measure. 

Figure 5 shows the response of a type-A sensor to propane. Several features strike the eye. First, the sensor is quite sensitive propane concentrations as low as 1 ppm are clearly detectable. Flowever, the steady-state response saturates at the same level of R 400 k 2, irrespective of the propane concentration. This is believed to be due to the glass substrate. Such substrate influences have been identified and discussed previously for other planar sensors [6,7]. Glass is an ionic conductor at elevated temperatures, and the equivalent resistance of the current paths through the glass substrate acts in parallel to the resistance R(f) of the IDE sensor proper. The total resistance R, R f ) can never exceed R, . This explanation was corroborated by measurements on a type-A sensor without sensitive layer. 

The quantitative relationship between SERS signal intensity and spore concentration is demonstrated in Figure 3A. Each data point represents the average intensity at 1020 cm from three samples with the standard deviation shown by the error bars. At low spore concentrations, the peak intensity increases linearly with concentration (Figure 3A inset). At higher spore concentrations, the response saturates as the adsorption sites on the AgFON... 

There is always some degree of adsorption of a gas or vapor at the solid-gas interface for vapors at pressures approaching the saturation pressure, the amount of adsorption can be quite large and may approach or exceed the point of monolayer formation. This type of adsorption, that of vapors near their saturation pressure, is called physical adsorption-, the forces responsible for it are similar in nature to those acting in condensation processes in general and may be somewhat loosely termed van der Waals forces, discussed in Chapter VII. The very large volume of literature associated with this subject is covered in some detail in Chapter XVII. 

The saturation magnetization, J), is the (maximum) magnetic moment per unit of volume. It is easily derived from the spia configuration of the sublattices eight ionic moments and, hence, 40 ]1 per unit cell, which corresponds to = 668 mT at 0 K. This was the first experimental evidence for the Gorter model (66). The temperature dependence of J) (Fig. 7) is remarkable the — T curve is much less rounded than the usual BdUouia function (4). This results ia a relatively low J) value at RT (Table 2) and a relatively high (—0.2%/° C) temperature coefficient of J). By means of Mitssbauer spectroscopy, the temperature dependence of the separate sublattice contributions has been determined (68). It appears that the 12k sublattice is responsible for the unusual temperature dependence of the overall J). 

Saturation is the concentration of a stimulus above which no increase in perception can be detected. It is tme that Weber-Stevens laws can predict the relationship between stimulus intensity and sensory response with some precision however, they do not describe the very common situation of stimuli at or near the threshold or point of saturation. 

The sacroplasmic proteins myoglobin and hemoglobin are responsible for much of the color in meat. Species vary tremendously in the amount of sacroplasmic proteins within skeletal muscle with catde, sheep, pigs, and poultry Hsted in declining order of sarcoplasmic protein content. Fat is also an important component of meat products. The amount of fat in a portion of meat varies depending on the species, anatomy, and state of nutrition of the animal. The properties of processed meat products are greatiy dependent on the properties of the fat included. Certain species, such as sheep, have a relatively higher proportion of saturated fat, whereas other species, such as poultry, have a relatively lower proportion of saturated fat. It is well known that the characteristic davors of meat from different species are in part determined by their fat composition. 

In addition to the effect of biological variabihty in group response for a given exposure dose, the magnitude of the dose for any given individual also determines the severity of the toxic injury. In general, the considerations for dose—response relationship with respect to both the proportion of a population responding and the severity of the response are similar for local and systemic effects. However, if metabohc activation is a factor in toxicity, then a saturation level may be reached. 

Water Transport. Two methods of measuring water-vapor transmission rates (WVTR) ate commonly used. The newer method uses a Permatran-W (Modem Controls, Inc.). In this method a film sample is clamped over a saturated salt solution, which generates the desired humidity. Dry air sweeps past the other side of the film and past an infrared detector, which measures the water concentration in the gas. For a caUbrated flow rate of air, the rate of water addition can be calculated from the observed concentration in the sweep gas. From the steady-state rate, the WVTR can be calculated. In principle, the diffusion coefficient could be deterrnined by the method outlined in the previous section. However, only the steady-state region of the response is serviceable. Many different salt solutions can be used to make measurements at selected humidity differences however, in practice,... 

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