Solute capacity factor concentration

Let us assume that there are three types of solid phases of phosphorus in wetland soils (Figure 9.31). Under alkaline conditions, these could be dicalcium phosphate (CaHP04) (A), octacalcium phosphate (Ca8(H2P04)g) (B), and hydroxyapatite (Ca5(P04)30H) (C). The stability of these phosphate solid phases can be explained by intensity and capacity factors. Intensity factor refers to the concentration or activity of ions in solution. Capacity factor refers to the amount and type of solid phase in soil. 

Temperature control is very important for obtaining reproducible separations. Indeed, the adsorption of the HR onto the stationary phase follows an adsorption isotherm hence, an increase of the column temperature leads to a decreased amount of the adsorbed HR, even if its concentration in the mobile phase is constant. This, in mrn, determines a decreased absolute surface potential and a modification of the solutes capacity factors. Usually, a temperature increase results in an improved resolution and faster separation, even if a reversal of the... 

Most detectors are concentration sensitive devices and thus the peak height will be proportional to the maximum concentration in the peak, which, in turn, will be proportional to the total area of the peak. The total area of the peak is proportional to the total mass of solute contained in the peak providing it is not excessively tailing. As the peak height is inversely related to the peak width, then, if peak heights are to be used for analytical purposes, all parameters that can affect the peak width must be held constant. This means that the capacity factor of the solute (k ) must remain constant and, consequently, the solvent... 

Retention in HIC can be described in terms of the solvophobic theory, in which the change in free energy on protein binding to the stationary phase with the salt concentration in the mobile phase is determined mainly by the contact surface area between the protein and stationary phase and the nature of the salt as measured by its propensity to increase the surface tension of aqueous solutions [331,333-338]. In simple terms the solvopbobic theory predicts that the log u ithn of the capacity factor should be linearly dependent on the surface tension of the mobile phase, which in turn, is a llne2u function of the salt concentration. At sufficiently high salt concentration the electrostatic contribution to retention can be considered constant, and in the absence of specific salt-protein interactions, log k should depend linearly on salt concentration as described by equation (4.21)... 

Where and are the stoichiometric fraction of the solute in each of its two forms A and AX, and k is the capacity factor at which the solute is observed to elute under the experimental conditions. Fj and can be expressed explicitly in terms of the equilibrium concentrations of A, X and AX and substituted into equation (4.22) to give... 

Table IV gives minimum steam requirement (infinite stages) at several different solution capacities. The factor attribu-able to equilibrium nonlinearity increases as more SO2 is absorbed, because the buffer capacity is consumed to a greater extent. Any capacity for SO2 absorption can be achieved by varying Na concentration (pH) in the solution. At low pH ([Na] = 1.5 M) the solution capacity for SO2 absorption is small, but the nonlinearity factor is also small (1.05). Solution capacity can be increased by operating at higher pH ([Na] = 2.5 M), but nonlinearity is more severe (1.32).

For Eq. (2) it is assumed that the volume of the micellar phase is proportional to the tenside concentration and that the partial molar volume v remains constant. (See Chapter 2.) A further prerequisite for the application of Eq. (2) is a constant ionic mobility of the micellar phase independent of the uptake of a solute (/x, . = const.). In contrast to HPLC, substances that have an infinitely high kP value, i.e., that are completely dissolved in the micellar phase, can be detected. In this case the sample molecule migrates with the mobility of the micelle. In the presence of several different micellar phases (coexistence of simple and mixed micelles), the calculation of kP is possible only when partial capacity factors are known (20). The determination of kP is then considerably more complicated. 

Self-Test M4.1B Inorganic cations can be separated by liquid chromatography according to their ability to form complexes with chloride ions. For the separation, the stationary phase is saturated with water and the carrier solvent is a solution of HC1 in acetone. The relative solubilities of the following chlorides in concentrated hydrochloric acid are CuCl2 > CoCI2 > NiCl2. Predict the relative values of the capacity factor k for the three salts. 

The quantity q of the solute in one of the phases is the product of the average concentration (c) of i in that phase (where the average is taken along the length of the column) and the volume of that phase. Hence, for the capacity factor (eqn.1.5) we find... 

The concentration of the counterion can be used to control the retention in IEC. It plays a role similar to that of the eluotropic strength of the eluent in RPLC or LSC, in that it affects retention much more than it does selectivity. The capacity factor can be related to the distribution coefficient of the solute (Dx) ... 

From eqn.(3.84) and figures 3.22a, b and c we conclude that the concentration of counterions in IEC is a primary parameter which may be used to vary retention, i.e. to bring the capacity factor into the optimum range. Only the selectivity between solutes of different valencies will be affected considerably by changes in the concentration of the counterion. 

In LC the solute bands may be concentrated on a pre-column, which is eluted with a weak eluent (low eluotropic strength). A simple way in which the effective injection volume may be reduced considerably is by dissolving or diluting the sample in a solvent that is much weaker than the eluent [707]. This has the effect that the initial capacity factor during... 

As noted, the retention of a polypeptide or protein with HP-IEX sorbents primarily arises from electrostatic interactions between the ionized surface of the polypeptide or protein and the charged surface of the HPLC sorbent. Various theoretical models based on empirical relationships or thermodynamic considerations have been used to describe polypeptide and protein retention, and the involvement of the different ions, in HP-IEC under isocratic and gradient elution conditions (cf. Refs.6,19 33 40,78-90). Over a limited range of ionic strength conditions, the following empirical dependencies derived from the stoichiometric retention model can be used to describe the isocratic and gradient elution relationships between the capacity factor In and the corresponding salt concentration [C,] or the median capacity factor In k ex, and the median salt concentration [C,] of a polypeptide or protein solute, namely,... 

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