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LOD Formula:
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The Limit of Detection (LOD) calculation determines the lowest concentration of an analyte that can be reliably detected by an analytical method. It is calculated from calibration curve data using the standard deviation of the response and the slope of the calibration curve.
The calculator uses the LOD formula:
Where:
Explanation: The equation accounts for the variability in measurements (SD) and the sensitivity of the method (slope) to determine the minimum detectable concentration.
Details: Accurate LOD determination is crucial for method validation, ensuring reliable detection of low analyte concentrations, and meeting regulatory requirements in analytical chemistry.
Tips: Enter standard deviation in concentration units and the slope value from your calibration curve. Both values must be positive numbers.
Q1: Why use the factor 3.3 in the LOD calculation?
A: The factor 3.3 corresponds to a 99% confidence level for detecting the analyte above the blank signal, assuming a normal distribution of measurements.
Q2: How is the standard deviation determined for LOD calculation?
A: The standard deviation is typically calculated from multiple measurements of a blank sample or a sample with very low concentration of the analyte.
Q3: What's the difference between LOD and LOQ?
A: LOD (Limit of Detection) is the lowest detectable concentration, while LOQ (Limit of Quantification) is the lowest concentration that can be quantified with acceptable precision and accuracy, typically calculated as 10×SD/slope.
Q4: When should LOD be determined?
A: LOD should be determined during method validation and whenever there are changes to the analytical method that might affect sensitivity.
Q5: Are there limitations to this LOD calculation method?
A: This approach assumes normal distribution of errors and linear response. It may not be appropriate for non-linear calibration curves or methods with non-normal error distributions.