Gradient elution segmented

Figure 25-13 Gradient elution of the same mixture of aromatic compounds in Figure 25-12 with the same column, flow rate, and solvents. The upper trace is the segmented gradient profile, so named because it is divided into several different segments.

Since one does not know what degradation products will form, gradient elution should be used. This significantly increases the chances that degradation products which are much more polar than the parent compound will be pulled away from the solvent front and those which are much less polar than the parent will elute from the column. Often the use of a multi-step gradient is particularly beneficial. The first segment of the multi-step gradient... 

We have seen in chapter 3 (table 3.10 b-d) that the composition of the mobile phase is a primary parameter in various forms of LC (LLC, RPLC, LSC). Gradient elution is only relevant for the latter two techniques, because the LLC system is not compatible with mobile phase gradients. Figure 6.6a shows a typical gradient program for LC. The complete program can be divided into a number of segments. 

The program starts and ends at the purge segment (P). The reason for this is related to the typical baseline observed in a gradient elution LC experiment (figure 6.6b). Unlike the situation in GC, the main cause of the blank signal in programmed solvent LC is formed... 

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