Signal-to-Noise Ratio Calculator (USP / Ph. Eur. 2H/h)

Measure S/N the pharmacopoeial way and estimate LOD and LOQ from one injection.

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Peak height H µV or mAU

Peak-to-peak noise h same unit

Concentration injected e.g. µg/mL

Example: a 0.50 µg/mL standard. Measure noise over a blank region about 20 peak widths long.

S/N–

Conc. at S/N 3–

Conc. at S/N 10–

S/N = 2H/h · LOD ≈ C × 3/(S/N) · LOQ ≈ C × 10/(S/N)

How it works

USP <621> and Ph. Eur. 2.2.46 define signal-to-noise as S/N = 2H/h, where H is the peak height from the extrapolated baseline and h is the peak-to-peak background noise of a blank injection, observed over a distance equal to at least 5 times (Ph. Eur. asks for 5, older USP text 20) the peak width at half height.

ICH Q2 accepts S/N of about 3:1 for the detection limit and 10:1 for the quantitation limit. The concentration estimates here assume a linear response through zero near the limit, so confirm them by injecting a standard at the estimated level.