Solute capacity factor

For optimization of chromatographic separations the ratio of the time spent by the solute in the stationary phase to the time it spends in the mobile phase is more fundiwentally i tortant. This ratio is called the solute capacity factor and is given by equation (1.8)... 

The terns k, and kj are the solute capacity factors in the Mobile phase, V, the volune of the nonolayer of adsorbed solvent per unit nass of adsorbent, w the weight of adsorbent (gn), V the colunn... 

Several theoretical models, such as the ion-pair model [342,360,361,363,380], the dyneuaic ion-exchange model [342,362,363,375] and the electrostatic model [342,369,381-386] have been proposed to describe retention in reversed-phase IPC. The electrostatic model is the most versatile and enjoys the most support but is mathematically complex euid not very intuitive. The ion-pair model emd dynamic ion-exchange model are easier to manipulate and more instructive but are restricted to a narrow range of experimental conditions for trtilch they might reasonably be applied. The ion-pair model assumes that an ion pair is formed in the mobile phase prior to the sorption of the ion-pair complex into the stationary phase. The solute capacity factor is governed by the equilibrium constants for ion-pair formation in the mobile phase, extraction of the ion-pair complex into the stationary phase, and the dissociation of th p ion-pair complex in the... 

Presented in Table I are the dimensions and properties of the several columns prepared in this work. The internal diameter was varied as shown from 0.278 mm to 0.0345 mm, while the stationary-phase film thickness was held constant for all but the last of the columns. Thus, the phase ratio (V] /Vc) decreases on passing from column 1 to 6 over the range 231.5 to 54.25. The solute capacity factors increase accordingly from 6.83 to 29.47. The number of theoretical plates per meter leng N/m for all columns except the first is therefore very nearly equal to the number of effective theoretical plates per meter, since the capacity factors are close to or exceed 10. 

The solute capacity factors measured at the optimum linear carrier velocity increase monotonously as the inverse of the column diameter, as shown in Figure 2. This result is to be expected, since the phase ratio decreases in the same fashion. However, since the mobile-phase volume decreases geometrically x on reducing the column radius, raw analysis times for a givmi linear carrier velocity, while longer with the columns of smaller ID, are not inordinately so. The values of tjjm (min m ) for columns 1 to 6 respectively were 2.38, 2.56, 2.62, 2.6 3.03, 3.63, while column 7 gave 3.14 (see below). 

Therefore, any column that is packed well for ultrahlgh resolution LC separations does not lose its maximum efficiency in SFC separations. However, the linear velocity (u) must be significantly higher, by a factor of at least three, to obtain the most efficient operation. Again, this is expected since the optimum linear velocity is inversely proportional to the particle diameter and directly proportional to the mobile phase/solute binary diffusivity (D12) and the solute capacity factor (k ) ... 

I = applied current (amps) kJcQ,kb = equilibrium constants Kd = fraction of pore volume available to a particular solute / = capacity factor (- g-)... 

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. 

As a solute is eluted, the distribution of its molecules along the longitudinal axes of the column changes, generating a Gaussian-like profile a band broadening effect whose maximum is known as time of retention as depicted in Fig. 1. This parameter, corrected for the time of retention of a solute, that is, not retained by the column (dead time, is related to the solute capacity factor k) by the relation ... 

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... 

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