Band broadening mechanisms

The above band-broadening mechanism assumes a more concrete form when it is described specifically for chromatography in Section 10.6. When this mechanism is expressed mathematically it becomes the nonequilibrium theory, an important tool describing zone evolution in chromatography (Section 10.6) and field-flow fractionation [2, 3J. 

Since the retention of the template on the imprinted polymers strongly depends on the sample load (see later Fig. 5.25), the theoretical models describing the various dispersion processes are not applicable. Nevertheless, on an imprinted CSP for L-PA, the least retained enantiomer, D-PA, elutes as a fairly Gaussian peak (Fig. 5.3), which should be governed by the same band broadening mechanisms that are considered in the models. A measure of the dispersion of a Gaussian peak is the deviation from its mean value, which is reflected in the reduced plate height as ... 

The van Deemter equation for plate height (H) as a function of flow rate (m) is the net result of the three band-broadening mechanisms just discussed ... 

The terms arise from the mechanisms of dispersion, or band-broadening, listed in Table 19.1. 

The hne-shape function gives the profile of the optical absorption (and emission) band and contains important information about the photon-system interaction. Let us briefly discuss the different mechanisms that contribute to this function, or the different line-broadening mechanisms. 

In this system the bands (zones) broaden because of diffusion effects and nonequilibrium. This broadening mechanism is fairly symmetrical and the resulting elution bands approach the shape of a Gaussian curve. This system best explains liquid or gas partition chromatography. The system may be viewed in two ways ... 

The five possible mechanisms of band broadening occur because of ... 

On the basis of the Q-band spectrum giving better resolution than that the X- and S-bands, we concluded that the dominant line-broadening mechanism at Q-band EPR was g-strain and that there was broadening in the X- and S- band spectra. From spectra simulation in the Q-band spectrum, we obtained the g principal values of gxx = 5.20, gyy = 4.75, and gzz = 2.24, and the g-strain tensor principal values <7gxx =1.11 (0.2), dgyy = 1.11 (0.2), and dgzz = 0.19(0.01). 

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