My background is peptide/protein separations where gradients are almost always used. I am now working with a small molecule and I have several collegeues who say it is unacceptable, particularly from a QC standpoint, to use a gradient method. I thought that today's equipment is good enough to reproduciably deliver a gradient consistently.
Can anyone give me convincing agruments either way??
Thanks.

We use gradients all the time in a GLP setting. As long as the instrument is qualified, there is no problem.

With peptide/protiens, you don't have much of a choice with gradient vs. isocratic. Now with small molecules you have a choice, and the key idea that I see here is the QC setting. One thought comes from the situation that methods used in QC are often developed in a research lab and handed down to the QC lab. Isocratic methods are easier pass down to labs with different and often older instrumentation.
Perhaps more importantly, a QC setting implies high throughput of samples. Remember that analysis time includes run time plus equilibration time if using a gradient. It may not seem like much, but with a high number of samples, that time can add up quickly. Isocratic eliminates the need for a requilibration time.

Noname,
1. Simplier is almost always better, prefer isocratic.
2. Isocratic baselines usually are more reproduceable, so the integrator works better.
3. GMP in pharm gives chromatographers fits. Explaining something to an auditor may cause pain when it is intuitively (common sense) obvious. Especially during validation for robustness, an isocratic method will allow easier proofs.
4. For one component prefer isocratic.
Jim

Consider that gradients lower separation proficiency for cases which work with isocratic methods. Being no friend of gradient HPLC I tried to get a RP analysis going of an antibody (MW ~ 150000)to no avail. It either stayed on the column or emerged ahead of the dead volume. Thusly, I agree with Brian and Jim: use gradients only if isocratic doesn´t work.

i worked in a GMP environment, as long as the instrument and method are validated, we didn't see any problem from FDA inspections. of course if in your sample there is only one component, no argument for isocratic, but what if there are several in the sample? gradient mostly gives better reproducibility and actually shorten the run time greatly compare to the price of re-equil. time.
anyway i don't think the word "unacceptable" is appropriate. it is true that most USP methods use isocratic but i think it considers all case of instrument conditions, some people may just still use old ones.

The issue is that the gradient delay volume of different instruments is different. Therefore, if you run exactly the same gradient, you will get different retention times from different instruments. If you have not learned to eliminate this problem from your procedure, the QC department will have fits trying to make your method work on different instruments. This is not an issue with isocratic methods.

From a QC manager point of vue, you should
ALWAYS develop your methods hand in hand
with QC; having the needs and specific
limitations of the QC in mind. They are your
customer. As for gradient vs isocratic, it is a
fact that when chromatographing a series of
sample preps within the same batch run, it is
preferable to have an isocratic method
especially if the Rt of the components are not
too high. Otherwise, Brian, Jim and Uwe gave
you prety good advise.

Go see your QC friends and ask them what
they need/want.

Hope it helps.

Guy