What a stability-indicating method is and how you demonstrate one — one year on

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).

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 #14 rather than contradicting it.

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.

I read post #16 twice before replying, because I had assumed the opposite.

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.

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.

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.

I read post #21 twice before replying, because I had assumed the opposite.

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.

This follows post #21 rather than contradicting it.

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.

Specificity: the method can distinguish the intended compound from related impurities and degradation products. Tested by comparing results on pure compounds, mixtures of compounds, and degraded samples.

Thank you for the correction. I have edited my earlier post with a note rather than silently, so the thread still makes sense to read. The error was mine and it was the kind that comes from remembering a figure instead of looking it up.

Transfer between laboratories: a method can be transferred from one lab to another, but the receiving lab needs to demonstrate that they can achieve the same performance. This requires comparative testing and sometimes small method refinements.

Picking up post #25: that is the part I would want checked first.

Stability-indicating method: one that can separate a compound from its degradation products. Critical for assay methods that claim to measure actual degradation (as opposed to purity, which is orthogonal).

Worth separating two things that post #25 runs together.

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.

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