Tracking gradient elution column performance

[peptidemetdev]

I know that the equations for resolution, asymmetry and so on don't really apply to gradient elution methods.

Is there an industry standard way to track column performance/system suitability with gradient elutions, or is it a general practice to use an isocratic method for column performance and system suitability, even when the analysis uses a gradient method?

[Uwe Neue]

The most practical method to test column performance is the assay itself. After all, your target is a reproducible and reliable assay.
For gradient applications, measure the resolution between critical pairs and set criteria for this parameter. You can also specify separately the peak width and the retention times. This is better than resolution, since it gives you a bit more information: in the case of a failure of the resolution criterium, which is important for the application, the other two criteria will tell you why it failed. If the peaks are getting wider, the column performance has most likely deteriorated. In the case that retention is changing, it can be one of the many things that change retention, from column aging to errors in the mobile phase make-up.