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Limit of Detection Formula:
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The Limit of Detection (LOD) is the lowest concentration of an analyte that can be reliably distinguished from the absence of that analyte (a blank value) within a stated confidence limit. It's a fundamental parameter in analytical chemistry and quality control.
The calculator uses the standard LOD formula:
Where:
Explanation: The formula uses the 3-sigma rule, where 3 times the standard deviation divided by the calibration curve slope gives the minimum detectable concentration.
Details: Accurate LOD determination is crucial for method validation, quality control, regulatory compliance, and ensuring the reliability of analytical measurements, especially at low concentration levels.
Tips: Enter the standard deviation (SD) and slope (S) values from your calibration data. Both values must be positive numbers greater than zero.
Q1: What's the difference between LOD and LOQ?
A: LOD (Limit of Detection) is the lowest detectable amount, while LOQ (Limit of Quantification) is the lowest quantifiable amount with acceptable precision, typically calculated as 10×SD/S.
Q2: How many measurements are needed for reliable LOD calculation?
A: Typically, at least 7-10 replicate measurements of a blank or low-concentration sample are recommended for reliable standard deviation calculation.
Q3: Can LOD vary between instruments?
A: Yes, LOD is method- and instrument-specific. Different analytical systems will have different detection limits for the same analyte.
Q4: What factors affect LOD?
A: Instrument sensitivity, sample matrix effects, background noise, analytical method, and operator skill can all influence the detection limit.
Q5: How often should LOD be verified?
A: LOD should be verified during method validation and periodically thereafter, especially after instrument maintenance or significant changes to the analytical procedure.