Detection and quantitation limit study

ICH Q2(R2) §§8.5–8.6 offers several approaches to the detection and quantitation limits, and the σ/S family is three of them: LOD = 3.3 σ/S and LOQ = 10 σ/S, where S is the slope of the calibration line and σ is the standard deviation of the response. The guideline accepts the standard error of the y-intercept, the residual standard deviation of the regression, and the standard deviation of blank measurements as that σ — and on the same data they give materially different limits.

This page reports every route your inputs support rather than choosing one for you, because choosing is a decision the study protocol makes, not the software. Whichever you claim in the report, the guideline expects the limit to be subsequently validated — by analysing an independent sample prepared near it.

A σ that is zero, or so small against the responses that it is only the rounding floor of the arithmetic, reports no limit at all and says so. A perfect fit through a set of standards is not evidence that a method can detect nothing; it is evidence that the standards had nothing left over to measure.

If your study already has a calibration curve, enter it on the Linearity tab instead — that section fits the line and reports the limits its own residual standard deviation and intercept standard error support, with no retyping. This section is for the routes that have no curve on the page: replicate blank readings, or a dedicated low-level curve fitted elsewhere whose slope and σ you are carrying across.

The limits carry whatever units the slope and σ were expressed in. A σ in response units divided by a slope in response units per mg/L gives a limit in mg/L, and no unit conversion happens here — the arithmetic is stated so it can be checked by hand.