Specificity, linearity, accuracy, precision, range, robustness — with real criteria — a second dataset

Thank you — that answers what I came here to find out.

Where I part company with post #16, and it is a narrow parting.

Two things can be true about Specificity at once: the mechanism is plausible and the evidence for the size of the effect is thin. Most of the argument here is people defending the first against attacks on the second.

Specificity is the first question: does the method separate the analyte from everything reasonably expected to be present? A method that has not been challenged with its own degradation products has not answered it.

I would call that likely rather than established.

On post #22 — agreed on the reasoning, with one qualification.

Accuracy: the method measures what you intend to measure. For purity methods, this is tested by spike-and-recover experiments: add a known amount of impurity to a sample and measure whether you recover the added amount.

Someone will know this better than I do and I hope they say so.

Confirming post #37 from a second method, which matters more than confirming it from a second person.

Reframing Specificity slightly, because I think the disagreement is about the question rather than the answer. If the question is "does it happen", yes. If it is "how often", nobody here knows.

System suitability: injections run at the start of a batch to establish that the instrument and column are performing. Acceptance criteria typically include replicate precision (RSD ≤2%), peak tailing (0.8–1.5), theoretical plates (>2000), and resolution (>1.5).

Worth one more sentence than it usually gets.

Limits of detection and quantitation: LOD is the lowest concentration that produces a signal above background. LOQ is the lowest concentration at which the method meets precision and accuracy acceptance criteria. Both are determined empirically.

If anyone has run this properly I would rather read that than my own guess.

Linearity: the detector response is proportional to compound concentration across the working range. Demonstrated by running standards at multiple concentrations and showing R-squared values typically ≥0.99.

Someone should write this up properly, and it should probably not be me.