Ionization salt concentration

Due to the significant reduction in ionizable salt concentrations, RO systems are often used as a pretreatment method before a DI system. An RO before a DI reduces the size of the deionizer, reduces the consumption of regenerate chemicals and may reduce the length of the deionizer required service cycle. 

Buffer salts also can exert a secondary salt effect on drug stability. From Table 5 and Fig. 5 it is clear that the rate constant for an ionizable drug is dependent on its pKa. Increasing salt concentrations, particularly from polyelectrolytes such as citrate and phosphate, can substantially affect the magnitude of the pKa, causing a change in the rate constant. (For a review of salt effects, containing many examples from the pharmaceutical literature see Ref. 116.)... 

Mass spectrometers that use electrospray ionization (ESI) do not function well if the eluent contains low volatility salts. This is a major concern when an ion-exchange column is used as a first-dimension column and the salt concentration is used to modulate the retention in this column. In this case, another valve can be connected between the second-dimension column and the detector so that any salt from the second-dimension elution process that is either unretained or weakly retained can be diverted prior to feeding zones to the mass spectrometer. 

The interactions between bare mica surfaces in 10 and 10 M KNO solutions were determined at pH = 3.5. In both cases an exponential type relation F(D) = 0-lcD was indicated, with decay lengths 1/k = 1.4 nm and 8 nm for the two salt concentrations, respectively, but with an effective surface potential tp = 40 mV, considerably lower than its value at the higher pH used in the PEO experiments (figure 6a, curve (a)). The lower value of p is probably the result of a lower net degre of ionization of the mica surface in the presence of the large H1" concentration (the low pH was used to ensure full ionization and polyelectrolyte). 

Coulombic, van der Waals, entropic and osmotic forces are coupled in a nontrivial way and give rise to important charge regulation in polyelectrolyte systems. The salt concentration is also an important factor to define the structure and thermodynamic properties of polyelectrolyte solutions. In weak polyelectrolytes the ionization equilibrium is also coupled to these interactions and thus the pKof ionizable groups depends on the organization of the interface and differs from that for the isolated molecule. 

Three causes of extractant solubility in the aqueous phase may be distinguished solubility of un-ionized and ionized extractant and metal-extractant species. For extractants such as acids, amines, and chelating reagents, their polar character will always result in some solubility in the aqueous phase over the pH range in which they are useful for metal extraction. Solubility depends on many factors including temperature, pH, and salt concentration in the aqueous phase, as discussed in Chapter 2. 

The composition of the subsurface gas phase may change as a result of gas dissolution into the liquid phase. The solubility of gases in water depends on the type of gas, temperature, salt concentration, and the partial pressure of the gases in the atmosphere. The most soluble gases are those that become ionized in water (CO, NHj, H S), while and are much less soluble (Table 1.2). 

This prediction is supported by the retention ctor data shown in Fig. 44 which includes both neutral and hmized eluites. It is inteitsting to note that the limiting slopes of the log A vs salt concentration plots at high salt concentrations is the same for both neutral and ionized species in Fig. 44. This behavior is expected in this example because the slopes are determined by the area change upon binding the eluite to the stationary phase which is about the same for both types of substances due tQ their similar molecular dimensions. 

This definition of x and y is more realistic at low and moderate salt concentrations and is in agreement with that of Sada and Morisue (17). Broul and Hala also assumed complete salt dissociation. The assumption of full dissociation of the salt may not be entirely valid at high salt concentrations, especially where the concentration of the nonaqueous solvent is also high. However, even in those instances where the assumption of full dissociation of the salt may be invalid, it appears to describe the system better than ignoring salt ionization completely. The terms x/ and y/ are referred to hereafter as ionic mole fraction and ionic activity coefficient, respectively. These should not be confused with the mean ionic terms used by Hala which are also based on complete salt dissociation, but are defined differently. No convergence problems were encountered when the ionic quantities were employed. 

Ionization reactions have been investigated (I) by a variety of methods that lead to reasonably accurate values of equilibrium constants over rather wide ranges of temperatures, pressures, and dissolved salt concentrations. However, the status of measurements leading to ionization constants in aqueous organic mixed solvents has not been developed nearly so well, in spite of the excellent work of Harned, Grunwald, Bates, and others (1-10). Experimental methods have been difficult and those methods that utilize the hydrogen electrode can be applied only to systems in which there are no complicating reduction reactions. 

The osmotic coefficients around 0.15—0.17 correspond to an effective degree of ionization /os 0.1, which is markedly lower than the value for fa determined from a fit of the radius of gyration (see Tables 3 and 4), but compare well to the data taken at high salt concentrations as discussed in Sect. 2.4.2. Corresponding data for a NaPSS of contour length around... 

The polyelectrolyte chain consists of A monovalent charged monomers. The chain is immersed in an aqueous solution. The volume of the system is V. The solution is electroneutral. If the number of counterions adsorbed on the surface of the polyion is M, then the degree of ionization is given by / = 1 — M/N [48]. The salt added to the solution is completely dissociated into n co-ions and n counterions. The salt concentration is, therefore, cs = n /V. 

The degree of ionization/ and the scaled expansion parameter l as a function of the various parameters that enter the model are obtained by minimizing the total free energy. Analysis revels that the degree of ionization decreases if the chain flexibility or the salt concentration increases [48]. This decease is also observed if the chain length or the dielectric constant is decreased [48],... 

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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