HPLC System Precision

[Chris]

For an analytical method we have set a criteria of an RSD of 2.0% or less for the repeatability of six standard areas at the start of the run and a limit of 2.5% or less for all of the run.

We typically see values of 0.5% and 1.0% for the first six and all standards respectively and over 50+ runs have not exceed 1.0 and 2.0%, should I reduce the criteria in respect of what we areactually obtaining or will I be creating a rod for my own back and increasing the risk of failure?

Thanks
Chris

[DR]

What we do -

For dilute samples (dissolution samples of things with weak chromophores, low area counts) - we go with a 5% limit on standard RSD for initial standards and we stick with it for the run. If RSD strays above 5%, we'll try nested bracketing and reinject any sample sets not bounded by standards that meet the 5% criterion.

For more concentrated samples, it is as above but with a 2% criterion.

[Chris]

Also, do you think a target retention time of 9.0 to 12.0 minutes is too wide?

[DR]

We do not set windows in our methods. We specify that the chromatograms look approximately like the example(s) provided. We also typically specify a minimum resolution between whatever the critical peak pair is for a given method.