Chromatography Forum

Hi,

I have got a deficiency letter from one authority that wants me to add a column efficiency parameter in the SST of the submitted method (gradient RP-method)

I have replied once that it is not relevant to calculate theoretical plates for a gradient method (this is also clearly stated in the pharmacopeia). But I got everything back with the same request.

Is there another way to evaluate column efficiency than theoretical plates? I would really not like to add this to the method.

We had OTC cGMP products, and we never calculated column efficiency.

As you know, it is impossible to measure the plate number from a single gradient run. The trick is to either convince the "authority" of that fact, which seems to be difficult if they are ignoring the Pharmacopeia.

If your method specifies the conditions (column dimensions, flow, gradient profile) tightly, you could simply specify a maximum allowable peak width. If they continue to insist on a plate number, the path of least resistance is to simply calculate an "apparent" plate number using the isocratic formula. You and I both know this is "bovine manure", but if it keeps the regulators happy . . .

What about calculating the peak capacity and citing a seminal paper on the topic, e.g. Neue 2005, JCA, 1079? That might be what is closest to a measure of the plate number in isocratic mode. And if it indeed still does not work, there would still be Tom's suggestion for an apparent plate number...

Or tell the regulator that you will incorporate the calculation that they provide, and see what they can come up with. That might convince them to not require it if they can't find it.

If the regulator can't tell you how to do it, then how can they know if what you include is accurate?

Or tell the regulator that you will incorporate the calculation that they provide, and see what they can come up with.

No doubt, the regulator will simply suggest calculating the plate number with the standard (isocratic) formula.

I would go too for th peak capacity : gradient duration (excluding recond. and part before the inj. spike ) divided by peak width of you main peak