Plate, effective plates theoretical, definition

In order to estimate resolution among peaks eluted from a chromatography column, those factors that affect N must first be elucidated. By definition, a low value of Hs will result in a large number of theoretical plates for a given column length. As discussed in Chapter 11, Equation 11.20 obtained by the rate model shows the effects of axial mixing of the mobile phase fluid and mass transfer of solutes on Hs. 

The major reason why a reduction of the particle size or column diameter is expected to lead to an increase of separation speed (resolution power per time unit) can be found in its effect to decrease r. Separation speed is often expressed in the analytical literature in terms of the number of theoretical plates N per time unit f (for a definition of N in terms of experimental parameters see Sect. 3.1.1). For zone dispersion due to lateral non-equilibrium, the ratio N/t will be in general inversely proportional to r [20] ... 

HETP Height equivalent to a theoretical plate. A measure of the combined effects of axial mixing and finite mass transfer resistance in causing deviations from ideal (equilibrium) behavior in a chromatographic column or in a countercurrent contact system. The definitions of HETP in these two cases are somewhat different,... 

Column effects. In order to establish optimal operating conditions, it is useful to consider the effects of system parameters on the resolution characteristics of an HDC system. HDC has been described as a chromatographic method with very low capacity but very high efiBciency. For example, the calibration curves show that the spectrum of sizes from less than 100 nm to greater than 300 nm is encompassed in less than about 5% of the column void volume. On the other hand, the theoretical plate count corresponding to the marker peak is typically in the range of several thousand per foot. Comparisons in terms of the specific resolution factor, enable a more precise analysis, since both the separation factor and peak dispersion are included in its definition. A simple form for the specific resolution between two particle populations of diameter Dpi and Dp2 is [11]. 

Capillary zone electrophoresis (CZE) is an effective technique for the definitive verification of the chromatographic purity of the target compound because of the large number of theoretical plates obtainable. The advantages of CZE, such as the possibility of analyzing for relatively labile species because of the absence of chromatographic packing, must be... 

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