Volume displacement effect

Imbalance of fat metabolism involves increased blood lipid concentrations. This can result in disproportion between the serum water on the one hand and the lipids on the other. If the sample material is diluted (as in the Seralyzer system), this may result in a dilution that is too great, as a result of the volume displacement effect of the lipids. The data obtained will be falsely lowered. 

To estimate the mass concentration of water in plasma a volume displacement effect by proteins and lipids has to be taken into account and is integrated in the mass concentration factor for standard plasma specimens. The correction factor for the mean specific volume of proteins is assumed to be 0.73 and 1.03 for lipids, respectively ... 

Electrolyte total concentrations are generally evaluated in samples diluted by an ionic strength and pH buffer in the so-called indirect method. Due to the known standardized background, calibration and calculation of the active ion molality based on the Debye-Hiickel formalism are allowable. Differences between indirect ISE assays and FAES or AAS are obvious and amount to 3-4% higher results for ISEs. They are most probably related to the volumetric dilution and the volume displacement effect by macromolecules relevant even in diluted samples. 

In most large automated biochemistry analyzers electrode concentrations are evaluated in the diluted sample by ISEs, by the so-called indirect method. A special compartment for the determination of sodium, potassium, and chloride is integrated. The ISEs have replaced flame photometry as well as coulo-metry to a large extent. However, the compatibility as well as interpretability of the results is problematic in many cases (see above). Since the ion-selective assays strictly respond to molal single-ion activities in the aqueous phase, the comparability to direct measurements is weak. A volume displacement effect by lipids and proteins even affects the accuracy and comparability in diluted samples with buffered ionic strength. 

A large one-sixth-scale model of the unloader hopper was selected so that flow patterns in the enclosure could be evaluated.Smoke was used to simulate the behavior of the lime dust in the enclosure. The lime drop from the clamshell was simulated by releasing coarse sand, thus modeling the flow patterns caused by the volume displacement and the air entrainment. The effects of local wind speed and direction on the enclosure were also simulated. 

Spherical turbulence promoters have also been used in tubular systems (Figure 31). In the author s experience, these spherical promoters are not as effective as detached spiral wire promoters (9). Particles collect in the dead stagnant areas between the spheres and foul the system. The spheres serve more effectively as volume displacement spheres than as turbulence promoters. 

Mass loadability of SPE and RAM columns play a key role in executing the sample clean-up. It is advisable to work below the overload regime of the column. Otherwise, displacement effects and other phenomena such as secondary interaction by adsorbed species might take place, which will lead to nonrepro-ducible results. This last statement is particularly important when the task is to monitor medium-to-low-abundance proteins large sample volumes in the milliliter range are therefore usually applied. 

The displacing effect observed in mixtures is not identical at all pressures. Lorenz and Wiedbrauck,16 in studying adsorption of mixtures of ethylene and carbon dioxide, found the adsorption of ethylene to be greater than that of carbon dioxide at low pressures, whereas at higher pressures this is reversed.17 Richardson and Wood-house18 observed that at 2870 millimeters pressure, carbon dioxide and nitrous oxide are adsorbed in almost equal volumes whereas at 72 millimeters pressure, two-thirds of the adsorbed gas is nitrous oxide. 

As the solids concentration in the suspension increases, interparticle distances become smaller and the particles start to interfere with each other. If the particles are not uniformly distributed, the effect may be a net increase in settling velocity, because the return flow due to volume displaced will predominate in particle-sparse regions (i.e., cluster formation). The cluster formation effect is significant only in suspensions that are nearly monodispersed. In practice, most suspensions are poly-dispersed and the clusters in such suspensions are short-lived. As a result, the settling rate steadily deteriorates with the increase in solids concentration because of the return flow being more uniform this is known as hindered settling. 

The effect of the insoluble material is to increase in absolute terms the solute effect. Physically, the insoluble material is responsible for part of the droplet volume, displacing the equivalent water. Therefore, for the same overall droplet diameter, the solution concentration will be higher and the solute effect more significant. 

If the sample size is increased, the shape of the peaks changes to rectangular (in the case of volume overload) or triangular (with mass overload) mixed forms and distorted peak shapes are also observed. Displacement effects can occur where a compound is pushed and concentrated by a following one that has a stronger affinity to the stationary phase. 

The approach-to-critical procedure is employed in each critical mass determination, and the rod worth is simul- -taneously determined for each etqieriment. The control rod worth, in terms of solution volume, varies from about 60 ml t high plutonium concentrationsy to about 560 ml (at low plutonium concentrations) as shown in Fig. 1. When the control rod is started into the solution (sphere. not full), the flux is observed to rise, then foil off as ex-pe ed. This is because the first portion of the rod is worth more as a volume displacement (improved geometry) than as a neutron absorber. The effect is estimated to te about 5f positive reactivity experimentally, and a perturbation calculation provides an estimate of 4.3f Ak/k. 

As a rule, in a mixed mobile phase a solvent peak appears near the void volume of the column. The appearance of the solvent peak may due to one of several effects, the first of which is the preferential solvation of polymers [172]. After dissolution in a mixed solvent, the polymer binds into its solvation shell one part of mixture to a larger extent. After the separation of the solvated polymer from rest of injected solvent, the solvent peak appears on chromatogram as was demonstrated by SEC [172] and under suitable condition [173] its area, or height, may be correlated with coefficient of preferential solvation [ 172]. An evaporation of one component from the sample bottle or displacement effects may also lead to appearance of a solvent peak [173]. The solvent peak represents a local change of composition of the mobile phase. Under critical conditions small changes of the mobile phase composition (for example, 0.1 % wt.) have a large influence on polymer retention, thus the solvent peak could influence the elution of the macromolecules. If so, this could imply that a tabulated critical composition is not precisely that, which really correspond to the critical conditions. The real, acting critical composition of eluent may be, and likely is, the composition somewhere, in the middle, of the solvent peak. The presence of the solvent peak influences especially pronouncedly the elu-... 

An unusual side effect of horn radiator efficiency and directional air mass coupling is that air overload can be encountered in horn systems above 120 dB. At these levels the air itself becomes nonlinear. The most troubling obstacle in large high-output systems are the harmonic distortions due to the compression volume being less than the volume displaced during rarefaction. See Fig. 3.53 (Tremaine, 1973, 1093). 

However, that s not the best optimization of vacuum application, and time. If a second cycle of incremental vacuum has great effect, so does a third total cycle Consider the following sequence of operation when the cleaning cycle is complete (1) fill the work chamber with one volume of air and displace it to the adsorber bed with another volume of air, (2) use the vacuum apparatus to create the same level of vacuum, (3) repeat step 1, (4) repeat step 2, (5) repeat step 1, (6) repeat step 2, and (7) repeat step 1. The calculated concentration of trichloroethylene in air exhaust after three incremental cycles of vacuum and three volume displacements is well below 1 ppm, and probably beyond the resolution of the calculation method This approach is partially illustrated in Table 2.9. 

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