FIA Gradient Techniques Single Zone

In addition to this vertical dimension, an FIA peak has also a horizontal dimension—the peak width. Again, a number of levels may be identified (Level 1, 2, and 3 in Fig. 2.16) each of which corresponding to two elements of fluid, with identical dispersion coefficients, one of them being situated at the leading edge of the peak, the other one on the trailing edge of the peak. The readout, peak width (W), can be identified by means of a selected level of response—as observed by the detector of choice. 

The third peak dimension, the peak area, is not as information rich as the horizontal and vertical readouts are, since the information contained within all elements of a dispersed sample zone is integrated into a single readout. One may visualize peak area measurement to be a numerical homogenization analogous to that achieved in batch analyses by homogeneous mixing. The relation between various peak readouts and concentration-response relationship is shown in Fig. 2.17. 

Rule 7. Since any dispersed sample zone is composed of a continuous concentration gradient, a desired degree of dispersion can be conveniently selected by locating the analytical readout within that element of fluid that has a suitable dispersion coefficient. 

The concentration gradient can be formed by injecting a single sample zone, as is described in this section, or by injection of two or several zones, as is described in the next section. The resulting readout may be— for both experimental approaches—either a single peak, as exploited in most FIA techniques designed to date, or a multiple peak, which yields additional information on sample composition. 

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