Chromatographic distribution

A properly tuned comprehensive 2-dimensional gas chromatograph distributes substances in the first dimension according to the strength of their dispersive interactions. .. and in the second dimension according to their specific non-dispersive... 

Another important parameter is the capacity factor, k which is a measure of the chromatographic distribution behaviour. Experimentally, k is computed from... 

The mass versus particle size distribution of several polymer latices with diameters in the range of 30 nm to 1500 nm was determined in less than 20 minutes using an integrated hydrodynamic chromatograph. Distributions obtained were compared with those found by other particle sizing techniques such as electron microscopy to verify validity of the technique. The instrument employed was able to analyze latices re-producibly with different optical properties, even though some of the injected particles may have been trapped within the column. Latex properties were correlated with particle size distribution data to illustrate the benefit of this particle sizing technique. 

A convenient way to classify solvents of chromatographic interest in terms of their polarity and the specific chemical interactions is the empirical scheme proposed by Snyder [214,215]. This scheme is based on experimental (gas chromatographic) distribution coefficients for three test solutes ( probes ) on a large number of stationary phases, which were published by Rohrschneider [216]. The probe compounds are ethanol (e), 1,4-dioxane (d) and nitromethane (n). The experimental values for the distribution coefficients undergo several empirical modifications ... 

As is evident from the preceding discussion, the retention behavior of a polypeptide or protein P- expressed in terms of the capacity factor k is governed by thermodynamic considerations. Peak dispersion, on the other hand, arises from time-dependent kinetic phenomena, which are most conveniently expressed in terms of the reduced plate height he, . When no secondary effects, i.e., when no temperature effects, conformational changes, slow chemical equilibrium, pH effects, etc. occur as part of the chromatographic distribution process, then the resolution Rs, that can be achieved between adjacent components separated under these equilibrium or nearequilibrium conditions can be expressed as... 

The chromatographic distribution coefficients K is defined as bound protein-free protein and can be modified to... 

Figure 3.9 Chromatographic distribution of a weak acid in reversed-phase liquid chromatography.

With such a system, one must slowly develop the chromatographic distribution pattern through the different zones. It may take from 8 to 36 hours for the pattern to be established. Other practical considerations are that the recirculation system must represent a small (< 10%) portion of a single... 

You have probably noticed that the CE mechanism actually does not include a chromatographic distribution mechanism. Consequently, it is as readily applicable to macromolecules as to smaller ones. Hence, it is valuable for the separation of large biomolecules. Chemical modification of the sihca wall or addition of detergents to the background electrolyte is often required to eliminate wall adsorption of proteins. 

Thin-layer-chromatographic distribution of opium alkaloids and some partially synthetic analogs... 

The classical differential kinetic method is based on the measurement of the kinetic characteristics of a system of two (as an exception) and three components entering into a reaction with a common reagent. This version is advisable for studying polymer systems that cannot be analysed directly by GC with the chromatographic-distributive method being used in some instances [29] in order not to introduce non-volatile polymeric compounds into the GC system. 

The distributions and relative ratios of sesquiterpanes and diamondoids may also have potential applications in investigation of oil and refined product spills. Stout et al. compared the chromatographic distributions of bicyclic sesquiterpanes of two weathered diesel fuel samples... 

Relations between the chromatographic distribution constant and the thermodynamic properties of the chromatographic system... 

Dependence of the standard differential molar Gibbs function of sorption and the chromatographic distribution constant on temperature and pressure... 

It follows from the discussion in this paragraph that only standard differential thermodynamic functions can be calculated from any chromatographic distribution constant defined in whatever way. Also, it is necessary to always specify the choice of the standard states for the solute in both phases of the system. Without specifying the standard states the data on the thermodynamic functions calculated from chromatographic retention data lack any sense. When choosing certain standard states it may happen that the standard differential Gibbs function is identical with another form of the differential Gibbs function, or includes such a form situations described by equations 46 and 49 may serve as examples. The same also holds true for standard differential volumes, entropies and enthalpies (compare Section 1.8.3). However, every particular situation requires a special treatment. 

Figure 4.20 Plot of the logarithm of an analyte s chromatographic distribution constant between mobile and stationary phases and column temperature for two different chemical compounds.

The chromatographic distribution coefficient, K, , which is used here as a tentative measure of the affinity of the sugars for polystyrene, was calculated by... 

The chromatographic distribution coefficient (K ) of monosaccharides and maltodextrins obtained with polystyrene gel (Bio-Beads SM-4) in water and salt solutions at 25°C . 

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