Capacity factor definition

Salt Effects. The definition of a capacity factor k in hydrophobic interaction chromatography is analogous to the distribution coefficient, in gel permeation chromatography ... 

A general approach to the problem of identification, should more definitive detectors not be available, is to change the chromatographic system , which in the case of HPLC is usually the mobile phase, and redetermine the retention parameter. The change obtained is often more characteristic of a single analyte than is the capacity factor with either of the mobile phases. 

Other results obtained from the ruggedness test are the definition of optimized method conditions for the factors and of system suitability criteria for a number of responses. System suitability parameters [6,17] are defined as an interval in which a response can vary for a rugged method. The system suitability criteria are the range of values between which a response (e.g. retention time, capacity factor, number of theoretical plates, resolution) can vary without affecting the quantitative results of the analysis. For instance, a design is performed and the retention time of the main substance varies between 200 s and 320 s without affecting the quantitative determination of the substances. The system suitability criteria for the retention time is then defined as the interval 200 s - 320 s. 

In this form of chromatography retention can readily be expressed in thermodynamic terms. The definition equation for the capacity factor (k) is... 

The definition of the retention index in terms of capacity factors is... 

By definition, all interpretive methods of optimization require knowledge of the capacity factors of all individual solutes. This is the fundamental difference between the simultaneous and sequential methods of optimization (sections 5.2 and 5.3, respectively) and the interpretive methods of section 5.5. Moreover, in the specific cases in which only a limited number of components is of interest or in which weighting factors are assigned to the individual solutes (see section 4.6.1) it is also necessary to recognize the individual peaks (at least the relevant ones) in each chromatogram. In section 5.5 we have tacitly assumed that it would be possible to obtain the retention data (capacity factors) of all the individual solutes at each experimental location. 

Substituting into the standard chromatographic definition of capacity factor (Equation 17), one obtains Equation 18. 

From the definition of the capacity factors and the F factor (see Example 11.1), alternative expressions for the gas and liquid loadings are... 

Any acid-base system of unknown distribution can be characterized fiilly with the help of two parameters. For example, in a solution of phosphates (Na salts), the equilibrium composition with regard to the six species (H3PO4, H2P0,T, HP04 , P04, H, and OH ) can be resolved completely if the concentration of at least two of the species or two of certain combinations thereof are evaluated analytically capacity factors such as [ANC] and [BNC] are especially valuable for defining acid-base systems in terms of conservative parameters. They can be determined frequently with ease and relatively good accuracy thus the discrepancy between conceptual and operational definition is very small. 

One has to distinguish between the ion concentration (or activity) as an intensity factor and the availability of the ion reservoir as given by the H-acidity or the deficiency of ions, or the alkalinity. Alkalinity and acidity are very important concepts although there are different ways to define these capacity factors, all definitions essentially relate to the proton condition at a given reference level. For the carbonate system, alkalinity [Aik] refers conceptually to the proton condition with reference to H2CO, H2O ... 

A mathematical description of the retention of ions under gradient elution conditions was introduced in 1957 by Schwab et al. [131]. It is based on parameters which are derived from the normal chromatographic elution process for which the eluent composition is kept constant during the separation. Hence, the retention of an ion at isocratic elution may be described according to Eq. (86), taking into account the definitions for the capacity factor, k, and the selectivity coefficient, K, [see Eq. (35) and (36) in Section 3.2] ... 

In modem chromatography it is more convenient to use the capacity factor (k or k ) instead of the distribution coefficient. The name retention factor has been suggested to replace the name capacity factor. The definition for capacity factor or retention factor is the same ... 

Fig. 3-7 [79] shows the dependence of required plates (N) on the sorbent selectivity (a) for compounds with various capacity factors k. In this plot the role o the capacity factor is exf essed by the function r. In Fig. 3-7 [79] each t value has a definite dependence N = 4(x), x = a - 1. 

Using the definition of the association constant K for a 1 1 complex and of the k (analogous to the capacity factor in (12)), the ratio of bound to free substrate molecules can be derived as follows ... 

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