AX-R12 — Peak asymmetry above the integration limit

A purity figure is only as good as the integration that produced it, and an integration is only reliable when the main peak is resolved from its neighbours and roughly symmetric.

The rule applies one criterion. Peak asymmetry above 1.50 — measured at 10 % of peak height, per Ph. Eur. 2.2.46 — means the trailing edge is dragging, and the boundary between the main peak and anything eluting after it becomes a matter of judgement rather than of geometry. That makes the reported purity a range rather than a number, and the range is wider than two decimal places suggest.

The index does not discard these records. It marks the purity figure integration-limited and keeps it out of the tightest aggregates. Asymmetry is a column-and-instrument finding rather than a material one: a worn frit, a void at the head of the bed, a sample solvent stronger than the starting mobile phase, or simply too much on the column. Re-injecting the same vial on a fresh column normally returns an asymmetry under 1.2 and a purity within measurement repeatability of the original figure.

The rule used to carry a second limb — resolution below 1.20 to the nearest named impurity. That limb has been removed. Resolution to whichever impurity happens to elute closest is a property of the compound's own impurity profile and of the gradient chosen, not a system-suitability criterion, and the index adjudicates nothing against it. Resolution is still computed and still printed on every record that has one, as a reported figure with no verdict attached, in the system-suitability block.