Why one laboratory's 98.4% and another's 96.1% may not contradict posts 31–38

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.

Precision and repeatability: within-run and between-run variability of the method. Acceptance criterion is typically a relative standard deviation of ≤2% for area measurements.

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.

On post #30 — agreed on the reasoning, with one qualification.

Robustness: the method gives consistent results when minor parameters vary. Tested by deliberately varying pH, temperature, flow rate, and mobile phase composition within reasonable ranges and demonstrating that results stay within acceptance.

This follows post #32 rather than contradicting it.

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).

Forced degradation studies: deliberately stress the material with acid, base, oxidant, heat, light to generate degradation products and demonstrate that the method can separate them from the parent peak. Acceptance is that the method is stability-indicating.

Range: the concentration range over which the method has been validated. Going outside the validated range is going outside the method's demonstrated performance.

Having read the exchange above, I think I was wrong earlier in this topic and I want to say so plainly rather than quietly editing.

The correction was fair and I had been repeating something I had not checked carefully enough.