Retention as a function

FIG. 22-75 Air fractionation by membrane. O2 in retentate as a function of feed fraction passed tbrougb tbe membrane (stage cut) showing tbe different result with changing process paths. Process has shell-side feed at 690 kPa (abs) and 298 K. Module comprised of hollow fibers, diameter 370 im od X 145 im id X 1500 mm long. Membrane properties (X = 5.7 (O2/N2), permeance for O2 = 3.75 X 10 Barrer/cm. Coutiesy Innovative Membrane Systems/ Fraxair)... 

Fig. 18. Tritium retention as a function of neutron damage tn graphite and graphite composite.

The co plAxlty of the retention proceas In RPC haa encouraged activity in non-chroaatographlc techniques to evaluate parameters appropriate for predicting retention as a function of mobile phase composition. Preliminary studies have indicated that solvatoChroaic methods can provide some useful insight into the retention process. The scale of solvent strength, based on... 

The complicated dependence of retention in supercritical fluid chromatography as a function of temperature and pressure is examined. Simple thermodynamic relationships are derived and discussed which allow the calculation of the slope of solute retention as a function of both temperature and pressure. 

Solute retention as a function of pressure at constant temperature is dependent on the partial molar vol mg of the solute in the stationary... 

Solute retention as a function of temperature at constant pressure is seen to be dependent on the partial molar enthalpy of solute transfer between the mobile and stationary phases, the neat capacity of the supercritical fluid mobile phase and the volume expansivity of the fluid. The model was compared to chromatographic retention data for solutes in n-pentane and CO2 as the fluid mobile phase and was seen to fit the data well. 

In this work we derive simple relationships between temperature, solute solubility and retention. The simple thermodynamic models developed predict the trend in retention as a function of pressure, given the solubility of the solute in the fluid mobile phase at constant temperature and the trend in k as a function of temperature at constant pressure. Our aim is to examine the complicated dependence of retention on the thermodynamic and physical properties of the solute and the fluid, providing a basis for consideration of more subtle effects in SFC. 

The derivation of the dependence of the trend in solute retention with temperature at constant pressure is similar to that described above for the trend in solute retention as a function of solute solubility and pressure at constant temperature. Once again making the same assumptions that led to eq. 6 and assuming temperature has a negligible effect on vstat, V Cat, and Vmob, differentiation of eq. 6 with respect to temperature at constant pressure yields... 

Solute retention as a function of pressure has been determined experimentally for a wide number of solutes over a range of temperatures and pressures.(1,23-25) The tcend in retention of a solute with pressure can be predicted within the limitations of our assumptions using eq. 11. The calculations are then compared with experimental data for the retention of naphthalene and biphenyl at various temperatures and pressures were obtained with supercritical CC. ... 

Figure 3 Retention as a function of pressure for naphthalene at 35.0°C. Solid line was predicted from eq. 11.

The thermodynamic relationship described in this article have been shown to describe the features of solute retention as a function of temperature at constant pressure and as a function of pressure at constant temperature (given the solubility of the solute in the fluid mobile phase). The dependence of retention upon temperature can apparently be ascribed to a combination of two effects. These effects Include the rapid change in the number of intermolecular interactions of the solute-solvent molecules as one progresses... 

Variation of solute retention as a function of the eluent pH. Conditions beta-cyclodextrin-silica pure aqueous eluent pH adjusted by HC1. Column temperature 30 C, eluent flow-rate 1 mL/min. 

Fig. 2. Anion exchange separation of trimethylammonium polyfethy-leneimine) Retention as a function of the filtration factor Z (ratio of filtrate volume to cell volume) (4% w/w, 0.01 M sodium salts, pH 8.5) [33]...

The same quadratic equations for retention as a function of composition have been... 

A minimum of four experimental data points is required to estimate the parameters in eqn.(3.58), similar to the experimental design employed by Snyder et al. [337]. Of course, eqn.(3.58) can only be applied over a limited range of compositions, for example the range over which 1 < k < 10. To describe retention as a function of both temperature and composition over wider ranges of the latter, more complicated equations need to be used. A quadratic equation for the relationship between retention and composition (eqn.3.38) can be combined with eqn.(3.57) to yield... 

The two applications shown here concern the optimization of the mobile phase composition in RPLC. However, the method may easily be adapted to other problems. It is most practical if straight retention lines can be obtained. It should be noted that this is not usually the case for retention as a function of mobile phase composition in RPLC. In fact, Colin et al. [555] adapted the value of the hold-up time (t0) such as to obtain straight lines. The fact that they succeeded in doing so for all of 11 solutes considered at the same time is remarkable, but it may not always be possible. In any case, adapting t0 in order to linearize the retention lines will be an awkward practice. 

Fig. 7. Activity retention as a function of monomer concentration in the immobilized enzymes by radiation polymerization method. Enzyme a-amylase(— 24 °C, 1 x 106 rad) glucose isomer-ase (—45°C, 1 x 106 rad) O a-glucosidase (—78°C, 1 x 106 rad) A glucoamylase (—78CC, 1 x 106 rad). Monomer HEMA (2-hydroxyethyl methacrylate)...

Since the flammability of materials increases with the ambient temperature, the LOI may be expected to decrease with increasing temperature. Johnson (1974) derived a quantitative experimental expression for LOI-retention as a function of temperature. Fig. 26.5 illustrates this. The LOI value decreases by the 3/2 power of temperature, which indicates that diffusion processes are more important than chemical activation of pyrolysis. From Fig. 26.5 the temperature can be derived at which any given LOI, measured at room temperature, will be reduced to 0.21. This will be the temperature at which the flammability of a material with a given LOI will permit candle-like burning in ordinary air. The result is given in Fig. 26.6. 

Results of hydrogen retention, as a function of incident ion energy, ion fluence, graphite structure and temperature, are presented, and their implication for ITER is discussed. During H+ irradiation of graphite, once the near surface is saturated, essentially all of the incident H+ is re-emitted from the surface -except for the small fraction that diffuses into the bulk - in the form of H2 molecules, H° atoms, and hydrocarbons. The relative amounts of these species depend on temperature. During post-irradiation thermal desorption spectroscopy, again FR, CH4, and H° are released. 

When the analyte mobile phase concentration is small, only a negligible fraction of the HR is in the form of a complex, hence its concentration [H] in the eluent can be considered invariant [3]. Both the pairing ion isotherm and the surface potential are unchanged by the presence of the sample ion [31,33]. In this case [20], analyte retention as a function of the mobile and stationary phase concentrations of the HR can be described, respectively, by the following expressions ... 

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