Capacity factor phase

Wells, M.J.M., Clark, C.R., Patterson, R.M. (1981) Correlation of reversed-phase capacity factors for barbiturates with biological activities, partition coefficients and molecular connectivity indices. J. Chromatogr. Sci. 19, 573-582. 

Stationary phase Capacity factor Asymmetry factor... 

M. J. M. Wells, R. C. Clark, and R. M. Patterson,/. Chromatogr. Sci., 19, 573 (1981). Correlation of Reserved-Phase Capacity Factors for Barbiturates with Biological Activities, Partition Coefficients, and Molecular Connectivity Indexes. 

The phase capacity factor (kf) is the net retention time relative to the nonsorbed time (to) and is therefore directly related to the distribution coefficient of a solute between two phases ... 

Mono- and disubstituted 4,4 -chalcones were the focus of two extensive studies [613]. A total of 48 E-S-cis- and Z-S-cis-chalcones were chromatographed on aminopropyl, diol, cyanopropyl, Cig, and Cg columns (2 = 270 nm) using a 97/3 heptane/THF mobile phase. Capacity factors for all compounds on all columns are... 

Diastereomeric mixtures of cyclic thiodipeptides (cyclothioalaninethioalanine, cyclothioalaninethioproline) were resolved as their l-fluoro-2,4-dinitrophenyl-5-L-alanine amides on a silica column (2 = 250nm, 254 nm, 270 nm, 279 nm, or 281 nm) using a 98/2 DCM/ethyl acetate mobile phase [790]. The separation, when scaled up to semipreparative levels, required a 95/5 DCM/ethyl acetate mobile phase. Capacity factors of <3.0 and separation factors greater than 1.2 were achieved. 

In a given volume of the micellar solution of the solute species i, the micellar phase capacity factor (see definition (1.4.1), also called the distribution ratio) may be... 

A solute s capacity factor can be determined from a chromatogram by measuring the column s void time, f, and the solute s retention time, (see Figure 12.7). The mobile phase s average linear velocity, m, is equal to the length of the column, L, divided by the time required to elute a nonretained solute. 

A useful guide when using the polarity index is that a change in its value of 2 units corresponds to an approximate tenfold change in a solute s capacity factor. Thus, if k is 22 for the reverse-phase separation of a solute when using a mobile phase of water (P = 10.2), then switching to a 60 40 water-methanol mobile phase (P = 8.2) will decrease k to approximately 2.2. Note that the capacity factor decreases because we are switching from a more polar to a less polar mobile phase in a reverse-phase separation. 

Changing the mobile phase s polarity index, by changing the relative amounts of two solvents, provides a means of changing a solute s capacity factor. Such... 

Haddad and associates report the following capacity factors for the reverse-phase separation of salicylamide (k i) and caffeine... 

B = Bottoms molar rate or subscript for bottoms c = Heat capacity (gas phase), Btu/lb °F CAF = Vapor capacity factor... 

The chromatography literature contains a vast amount of dispersion data for all types of chromatography and, in particular, much of the data pertains directly to GC and LC. Unfortunately, almost all the data is unsuitable for validating one particular dispersion equation as opposed to another. There are a number of reasons for this firstly, the necessary supporting data (e.g., diffusivity data for the solutes in the solvents employed as the mobile phase, accurate distribution and/or capacity factor constants (k")) are not available secondly, the accuracy and precision of much of the data are inadequate, largely due to the use of inappropriate apparatus with high extracolumn dispersion. 

The choice of variables remaining with the operator, as stated before, is restricted and is usually confined to the selection of the phase system. Preliminary experiments must be carried out to identify the best phase system to be used for the particular analysis under consideration. The best phase system will be that which provides the greatest separation ratio for the critical pair of solutes and, at the same time, ensures a minimum value for the capacity factor of the last eluted solute. Unfortunately, at this time, theories that predict the optimum solvent system that will effect a particular separation are largely empirical and those that are available can be very approximate, to say the least. Nevertheless, there are commercially available experimental routines that help in the selection of the best phase system for LC analyses, the results from which can be evaluated by supporting computer software. The program may then suggest further routines based on the initial results and, by an iterative procedure, eventually provides an optimum phase system as defined by the computer software. 

A computer program was compiled to work out the ray-tracing of UV detector of high performance capillary electrophoresis at the investigation of 5 and 6 (98MI59). The capacity factor of 5 at different temperature and at different mobile phase compositions was experimentally determined in bonded-phase chromatography with ion suppression (98MI15). 

This is because the increased turbulence from higher flow rates decreases the possibility for inclusion complexation, a necessary event for chiral recognition in reversed phase. Some effect has also been observed in the new polar organic mode when (capacity factor) is small (< 1). Flow rate has no effect on selectivity in the typic normal-phase system, even at flow rates up to 3 inL miir (see Fig. 2-11). 

Capacity factor based on tower area, ft/sec Capacity fector at flood, ft/sec Liquid gradient vapor load correction factor or Discharge coefficient (see accompanying table) or Gas phase loading factor, ft/sec. Equation 8-281 Eddy loss coefficient, dimensionless. Table 8-22 Wet cap pressure drop correction factor. Figure 8-115... 

If these changes are small (i.e., a current of 1 pA corresponds to an amount of about 10 10 mol/s only) and the capacity factor (e.g., charge density) in the involved phases is large, the mixed potential can be stable over a long period of time and... 

The time taken for an analyte to elute from a chromatographic column with a particular mobile phase is termed its retention time, fan- Since this will vary with column length and mobile phase flow rate, it is more useful to use the capacity factor, k. This relates the retention time of an analyte to the time taken by an unretained compound, i.e. one which passes through the column without interacting with the stationary phase, to elute from the column under identical conditions (to). This is represented mathematically by the following equation ... 

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. 

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