Estimate limits of detection and quantitation using ICH-recommended methods.
σ and Slope method (ICH Q2): Enter the standard deviation of the response (σ) and the slope (S) of your calibration curve. σ can come from the standard deviation of y-intercepts of multiple calibrations, residual standard deviation of the regression, or replicate blank measurements.
Signal-to-Noise method: Measure the S/N ratio at a known low concentration. The calculator extrapolates to find the concentration that would give S/N = 3 (LOD) and S/N = 10 (LOQ), assuming linear response.
ICH method: LOD = 3.3σ/S and LOQ = 10σ/S, where σ is the standard deviation of the response and S is the slope of the calibration curve in the region near the detection limit.
S/N method: LOD corresponds to S/N = 3:1 and LOQ to S/N = 10:1. If a standard at concentration C gives S/N = x, then LOD = C × 3/x and LOQ = C × 10/x (assuming linearity).
Worked example: A calibration curve has slope = 1250 AU/(µg/mL) and residual standard deviation = 0.0025 AU. LOD = 3.3 × 0.0025/1250 = 6.6 × 10⁻⁶ µg/mL = 6.6 pg/mL. LOQ = 10 × 0.0025/1250 = 2.0 × 10⁻⁵ µg/mL = 20 pg/mL.
Important: These are statistical estimates. Always verify experimentally by analyzing standards at the calculated LOD/LOQ concentrations and confirming acceptable precision (%RSD < 20% for LOQ) and accuracy.