Limit of Quantitation Calculator
Calculate limit quantitation with our free science calculator. Uses standard scientific formulas with unit conversions and explanations.
Reviewed by Manoj Kumar, Mathematics Educator
Formula
LOQ = 10 * SD / Slope | LOD = 3.3 * SD / Slope
LOQ is calculated as 10 times the standard deviation of the blank (or residual SD of regression) divided by the slope of the calibration curve. LOD uses a multiplier of 3.3. These multipliers correspond to approximately 95% and 99% confidence levels respectively per ICH Q2(R1) guidelines.
Worked Examples
Example 1: ICH Standard Deviation Method
Problem:Blank standard deviation is 0.025 absorbance units and the calibration curve slope is 1.5 AU per mg/L. Calculate LOQ and LOD.
Solution:LOQ = 10 * SD / Slope\nLOQ = 10 * 0.025 / 1.5\nLOQ = 0.250 / 1.5 = 0.1667 mg/L\n\nLOD = 3.3 * SD / Slope\nLOD = 3.3 * 0.025 / 1.5\nLOD = 0.0825 / 1.5 = 0.0550 mg/L
Result:LOQ: 0.1667 mg/L | LOD: 0.0550 mg/L | LOQ/LOD Ratio: 3.03
Example 2: Calibration Curve Regression Method
Problem:Five calibration standards give concentrations [0.1, 0.2, 0.5, 1.0, 2.0] mg/L and responses [0.15, 0.30, 0.75, 1.50, 3.00] AU. Calculate LOQ from residual standard deviation.
Solution:Linear regression: y = 1.5x + 0.0\nResidual standard deviation (Sy/x) from regression residuals\nLOQ = 10 * Sy/x / Slope\nLOD = 3.3 * Sy/x / Slope\nR-squared is near 1.000 indicating excellent linearity
Result:LOQ and LOD calculated from regression residuals with R-squared near 1.0
Frequently Asked Questions
What is the Limit of Quantitation (LOQ) and how does it differ from Limit of Detection (LOD)?
The Limit of Quantitation (LOQ) is the lowest concentration of an analyte in a sample that can be determined with acceptable precision and accuracy under stated experimental conditions. It differs from the Limit of Detection (LOD), which is the lowest concentration that can be reliably detected but not necessarily quantified. According to ICH guidelines, LOD is calculated as 3.3 times the standard deviation of the blank divided by the slope of the calibration curve, while LOQ uses a multiplier of 10 instead of 3.3. This means the LOQ is approximately three times higher than the LOD. The LOQ represents the practical lower boundary for reporting a numerical concentration value with confidence.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy