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LOD Formula:
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The Limit of Detection (LOD) is the lowest concentration of an analyte that can be reliably detected by an analytical method. It represents the point at which the measured signal can be distinguished from background noise with a specified level of confidence.
The calculator uses the LOD formula:
Where:
Explanation: The equation calculates the minimum detectable concentration based on the variability of blank measurements and the sensitivity of the analytical method.
Details: Accurate LOD determination is crucial for method validation, quality control, and regulatory compliance in analytical chemistry. It helps establish the lower limit of quantitation and ensures reliable detection of trace analytes.
Tips: Enter the confidence factor (typically 3), standard deviation of blank measurements, and the slope of the calibration curve. All values must be positive numbers.
Q1: Why is k typically set to 3?
A: A k value of 3 corresponds to a 99.7% confidence level in normal distribution, meaning there's only a 0.3% chance that a blank measurement would exceed this limit.
Q2: How is the standard deviation determined?
A: The standard deviation is typically calculated from multiple measurements of a blank sample or a sample with very low analyte concentration.
Q3: What is the difference between LOD and LOQ?
A: LOD is the lowest detectable concentration, while LOQ (Limit of Quantitation) is the lowest concentration that can be quantitatively measured with acceptable precision and accuracy, typically calculated as 10×SD/m.
Q4: Can LOD vary between instruments?
A: Yes, LOD is method and instrument specific. Different analytical systems may have different detection limits for the same analyte.
Q5: How often should LOD be determined?
A: LOD should be determined during method validation and periodically verified as part of quality control procedures, especially when there are changes in instrumentation or methodology.