Preliminary Remarks, General Conditions

Lately, to understand gradient elution we have carried out many gradient separations. Most of the measurements were performed by Hans-Joachim Kuss in Munich. With the aim of finding generally applicable rules, but also to verify the theory of gradient elution in practice, we have chosen very different chromatographic conditions, below and in short form the most important  

It goes without saying that the presentation of the results including examples exceeds by far the scope intended here. Therefore, the in our opinion most important results follow in condensed form further below. Some example chromatograms are intended to illustrate these findings. The fact that with UHPLC and Fast LC-systems narrow peaks and fast separations can be achieved is trivial. 

Here we only show examples obtained using the older system. Our intention is to show that with not very demanding separations diverse, even difficult gradients are quite possible with medium quality equipment. 

We have discussed the plate number earlier, it will no longer play a role here. We will concern ourselves rather with interactions, with the selectivity and the retention term in Eq. (3.1) the objective is sufficient resolution. We have treated the influence of the important parameters solvent (ACN against MeOH), pH and temperature on the selectivity in detail in Chapter 3 and partly in Chapter 5, reference is made here to these. Also, approaches for systematic pH-value, column, temperature and eluent screening through the automation of experiments (AutoChromSword, DryLab, ACDLabs) are not considered here, see Refs. [5, 6]. 

Case 1 The Gradient Duration Remains Constant and the Fiow is Increased 

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