System suitability injections: if they failed, the run did not happen — the long version

Gradient slope is the single biggest driver of apparent purity differences. A shallower gradient over a longer run resolves more impurities and gives a higher purity figure. A steep gradient produces a tidier-looking chromatogram with fewer visible peaks and gives a lower purity figure. Both are legitimate methods and they will not produce the same number.

I checked the source rather than the summary, and they differ.

Typical suitability criteria are a replicate area relative standard deviation below about two per cent, a tailing factor inside a defined window, a resolution minimum against a specified peak, and a plate-count floor.

The arithmetic in post #3 is right; the assumption feeding it is the part to check.

Gradient delay volume differs between instruments and shifts the whole chromatogram. It is why a transferred method rarely reproduces retention times exactly on a different system.

System suitability testing: injections run before and during the sample run to establish whether the instrument, column and method were performing when the sample was analysed. If suitability did not pass, the sample results from that run are uninterpretable.

Everything in post #3 holds. The case it does not cover is the one I have.

System suitability is not paperwork. If the replicate injections failed, the run did not happen — the numbers from it are uninterpretable rather than approximate.