Concentration dependence, partition

Sutde, C. A., Fuhrman, J. A., Capone, D. G. (1990). Rapid ammonium cycling and concentration-dependent partitioning of ammonium and phosphate Implications for carbon transfer in planktonic communities. Limnol. Oceanogr. 35, 424-433. 

Dietz, M. L., Stepinski, D. C. (2008). Anion concentration-dependent partitioning mechanism in the extraction of uranium into room-temperature ionic liquids. Talanta, 75, 598-603. 

Watson, E. B., Henry s law behavior in simple systrans and in magmas critraia for discerning concentration-dependent partition coefficients in nature, Geochim. Cosmochim. Acta, 49, 917-923, 1985. 

Dietz, ML. Stepinski, D.C., (2008). Anion Concentration-Dependent Partitioning Mechanism in the Extraction of Uranium into Room-Temperature Ionic Liquids. Talanta, Vol.75, pp. 598-603... 

In spite of these complexities, most analyses of extraction assume linear equihbria. The detailed chemistry appears as a concentration-dependent partition coefficient. While such concentration-dependent partition coefficients are beyond the scope of this book, they are well understood and discussed in detail in more speciahzed references. 

This trend can be explained with the following mechanism. In the presence of NAPL, the extracted vapor concentration depends mainly on the vapor pressure of the contaminant. After the disappearance of free NAPL, the extracted vapor concentration becomes dependent on the partitioning of contaminants among the three other phases (see Table 14.3). As the air passes through the pores, the dissolved contaminants volatilize from the soil moisture to the gas phase, causing the desorption of contaminants from the surface of soil particles into the aqueous phase. As a result, the concentration in all three phases decreases, with a consequent decrease in removal rates. 

In contrast, diffusion of MeOH measured via permeabilify measurements (assuming a partition coefficient of 1) was lower (1.3 x 10 and 6.4 x 10 cm s for Nafion 117 and BPSH 40, respectively) and showed no concentration dependence. The differences observed between the two techniques are related to the length scale over which diffusion is monitored and the partition coefficient, or solubility, of MeOH in the membranes as a function of concentration. For the permeability measurements, this length is equal to the thickness of the membrane (178 and 132 pm for Nafion 117 and BPSH 40, respectively), whereas the NMR method observes diffusion over a lengfh of approximately 4-8 pm. 

Paschke, A. and Schuurmann, G. Concentration dependence on the octanol/water partition coefficients of the hexachlorocyclohexane isomers at 25 °C, Chem. Eng. Technol, 23(8) 666-670,1998. 

These new methods for determining the partition coefficients of ionized species are still e3q>erimenta1, but they are presented in a spirit that they may stimulate thinking and further refinement. Single-phase titrations with HCl in octanol have only recently been run. A possible concentration dependency of pKa in the single-phase titrations has been suggested by a referee and will be looked for. Further refinement of the two-phase titrations may incorporate ion-pair association constants. 

Figure 4.4 Concentration dependence of the partitioning of a compound that forms an aggregate. In this figure, Cq and C are Cj(o) and Cj(, ) in Equation (4.35).

Elements present in only minor or trace concentrations are partitioned in quite different ways. These elements are not abundant enough to form their own minerals, so they must be incorporated into minerals composed of the major elements. Because they must fit into crystalline sites whose sizes and coordination are already fixed, the ease with which they can be included depends on ionic size and charge. Trace ions that fit nicely into sites otherwise occupied by major ions having similar sizes and charges are said to be compatible. Conversely, large ions with high charge, referred to as incompatible elements, tend to be excluded from most crystal sites. 

The thickness of the tissue, partition coefficient, and the diffusion coefficient are properties of the mucosa and cannot be altered. Designing appropriate formulations that heed the necessary conditions can vary the surface area for delivery of the drug, time of contact, and the free drug concentration. The partitioning of the drug into the membrane will depend on... 

Air-water partition coefficients and Flenry s law constants are strongly temperature dependent because of the temperature dependencies of vapor pressure and of solubility. FI is also slightly dependent on the temperature dependence of water density and, hence, molar volume. The constants may be concentration dependent because of variations in yw, although the effect is believed to be negligible at low concentrations of non-associating solutes. Noted that these simple relationships break down at high concentrations, i.e., at mole fractions in excess of approximately 0.01. For most environmental situations, the concentrations are (fortunately) usually much lower. For thermodynamic purposes, H is usually preferred, whereas for environmental purposes, H is more convenient. 

To solve Equation 93 it is necessary to know the characteristic functions of the cellular physiology, that is, the growth rate r(m, S), the cellular division rate T(m, S), and the cell mass partition function p(m, m, S). Since these functions are substrate concentration- dependent, the substrate consumption rate must also be defined. These substrate concentration variations are calculated using the yield coefficient Yx/s, that establishes a relationship between the growth rates and the substrate consumption rate. The consumption rate is indicated by Equation 94. 

Competition Between Pollutants. Competition between several organic pollutants may affect the photocatalytic degradation rate of each species, depending on whether the process is limited by the irradiation or by the total organic matter. The factors intervening in the competition are the respective concentrations, the partition coefficients between the fluid phase and the adsorbed phase, and the relative reactivities with respect to the active species. Consequently, interference effects may or may not be observed. 

Schiickler, F. and Lee, G. Relating the concentration-dependent action of Azone and dodecy-L-pyroglutamate on the structure of excised human stratum comeum to changes in drug diffusivity, partition coefficient and flux. International Journal of Pharmaceutics 80 81-89, 1992. 

When three dimensional particles were used instead of coatings, the diffusional and structural kinetics showed marked differences in the rates of mass to area in the concentration dependent regions of partition coefficient (lower temperature and mass sorbed). Thus, the fundamental assumption of the Kiselev Yashin equation that the mass/area ratio was equal for prepeak and peak regions was not met, and agreement with static data was fortuitous at best. 

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