Required plate number

FIGURE 6.1 A Poppe plot for the required plate number in conventional HPLC. The parameters are taken from Poppe s original paper (Poppe, 1997). The parameters are maximum pressure AP = 4x 107 Pa, viscosity / = 0.001 Pa/s, flow resistance factor

diffusion coefficient D= lx 1CT9 m2/s, and reduced plate height parameters using Knox s plate height model are A — 1, B— 1.5, C = 0.05. 

Required plate numbers. nne- The number of plates necessary for the separation of two components based upon resolution, R, of 1.5. S... 

REQUIRED PLATE NUMBER. Knowing the capacity factor, k1, and the separation factor, a, one is able to calculate the required number of plates (n ) for the separation of two components (the k value refers to the more readily sorbed component). 

We note, first of all, that t increases with N. Consequently, any step that will reduce the required plate number N will reduce t. For example, the use of a column that has high relative selectivity A KIK for a critical solute pair will reduce N (see Eq. 12.58) and thus t. Also, special detection techniques (such as multiwavelength UV detection) that make it possible to extract analytical information from partially overlapping peaks reduce the required Rs and thus, as shown by Eq. 12.58, the required N. 

For enantioseparation on CSPs in CEC, nonstereospecific interactions, expressed as 4>K, contribute only to the denominator as shown in Eq. (1), indicating that any nonstereospecific interaction with the stationary phase is detrimental to the chiral separation. This conclusion is identical to that obtained from most theoretical models in HPLC. However, for separation with a chiral mobile phase, (pK appears in both the numerator and denominator [Eq. (2)]. A suitable (f)K is advantageous to the improvement of enantioselectivity in this separation mode. It is interesting to compare the enantioselectivity in conventional capillary electrophoresis with that in CEC. For the chiral separation of salsolinols using /3-CyD as a chiral selector in conventional capillary electrophoresis, a plate number of 178,464 is required for a resolution of 1.5. With CEC (i.e., 4>K = 10), the required plate number is only 5976 for the same resolution [10]. For PD-CEC, the column plate number is sacrificed due to the introduction of hydrodynamic flow, but the increased selectivity markedly reduces the requirement for the column efficiency. 

In such separation problems the required plate number TV is given by the separation factor cZnjn of the critical peak pair , i.e. those two components of the mixture that are most difficult to separate. Consequently the optimizing strategy can also be developed... 

Dependence of the value of a on the difference in boiling points of the components and dependence of the required plate number on the fractionating factor Fr n(I) by formula (101)... 

Dependence of the required plate number on the reflux ratio for Rose s standard distillation... 

Mass rate of test substance entering detector Moles of a substance in a mixture mole fraction Required plate number... 

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