High mobile phases

Thus, a practical procedure would be as follows. Initially the HETP of a series of peptides of known molecular weight must be measured at a high mobile phase velocity to ensure a strong dependence of peak dispersion on solute diffusivity. 

As already stated, we shall not explain the details but refer the reader to the literature for further developments. However, we would stress that there are very large intrinsic differences between one- and two-dimensional nucleation, and these are likely to be important for highly mobile phases such as the hexagonal phase in polyethylene. 

Figure 4.9 Schematics of electrospray LC-MS interfaces with (a) a heated capillary and (b) a heated block to allow high mobile-phase flow rates. From applications literature published by (a) Thermofinnigan, Kernel Hempstead, UK, and (b) Micromass UK Ltd, Manchester, UK, and reproduced with permission.

FI Do you think these mass transfer effects would become more serious at low or high mobile phase flow rates ... 

Inorganic ions (e.g., LP, Na+, and K+) were separated by a silica rod column under hydrophilic interaction mode (HILIC) [198]. The studies of Pack and Risley showed amazing high efficiencies at high mobile phase flow rates by applying HlLlC conditions toward separation of inorganic ions. 

At high mobile phase velocities the equation for reduced plate height becomes approximately h/v = c. Under conditions required to obtain the maximum number of plates, the pressure drop tends to infinity. 

Introduction of all these materials on the market is driven primarily by then-superior stability at high mobile-phase pH and temperature range. 

C f, C o, and are the solute concentrations in the mobile phase at a moment t, before equilibrium and after equilibrium, respectively), A depends on Sp, B on the physical properties of the solvent system, and b on solutes and solvent system. This variation is very interesting, because it shows that a high mobile-phase flow rate decreases the retention time without decreasing efficiency. However, it was observed that Sp decreases with the flow rate and the resolution R, also decreases as described in the following section. The flow rate of the mobile phase may be increased to decrease the separation time, but, at the condition that Sp remain satisfactory to maintain a sufficient R, [2]. Finally, it has been shown that N increases with the centrifugal force field [2]. 

This noninvasive method could allow the differentiation between the various packing materials used in chromatography, a correlation between the chromatographic properties of these materials that are controlled by the mass transfer kinetics e.g., the coliunn efficiency) and the internal tortuosity and pore coimectivity of their particles. It could also provide an original, accurate, and independent method of determination of the mass transfer resistances, especially at high mobile phase velocities, and of the dependence of these properties on the internal and external porosities, on the average pore size and on the parameters of the pore size distributions. It could be possible to determine local fluctuations of the coliunn external porosity, of its external tortuosity, of the mobile phase velocity, of the axial and transverse dispersion coefficients, and of the parameters of the mass transfer kinetics discussed in the present work. Further studies along these lines are certainly warranted. 

If the second term of the RHS of Eq. 14.45 accoxmts for a fourth of the plate height, then the limit error made with a high value of k and bCo = 1 is only 25% under the most unfavorable set of experimental conditions. This illustrates the fact that deviations between experimental results and the prediction of the equilibrium-dispersive model will occur preferably at high mobile phase flow velocities. We see from Eq. 14.48 that the error introduced by the use of the equilibrium-dispersive model instead of a kinetic model decreases with increasing values of both Dakf/u = St/Pe and k /(1 -I- The value of D is of the... 

When the production rate obtained with a given coliunn is optimized, the max-immn production rate is achieved at high mobile phase velocities. The production rate depends heavily on the column efficiency xmder analytical conditions most of this efficiency is traded off for a short cycle time. 

As presented in the two previous subsections, several viable options exist for high throughput bioanalysis. It is interesting to note that an issue seldom discussed is the relative cost of the reagents and supplies associated with the various methods. For example, the issue of high mobile-phase consumption/waste-stream production in TFC may be a concern. A similar situation occurs with... 

The flat slope of plate height vs mobile phase velocity plot (Figure 7.2 a) in LC permits the use of high mobile phase velocity without much loss in column efficiency. In this respect, LC differs considerably from GC in which plate height varies more steeply with mobile phase velocity at large values of the latter (Figure 7.2 b). 

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