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Method Detection Limit Formula:
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The Method Detection Limit (MDL) is defined as the minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than zero. It's determined from the analysis of a sample in a given matrix containing the analyte.
The calculator uses the MDL formula:
Where:
Explanation: The MDL is calculated by multiplying the appropriate Student's t-value by the standard deviation of the analytical results.
Details: MDL is a critical parameter in analytical chemistry that defines the lowest amount of an analyte that can be reliably detected by a specific analytical method. It's essential for method validation, regulatory compliance, and quality control in laboratory testing.
Tips: Enter the appropriate Student's t-value for your degrees of freedom and confidence level, and the standard deviation of your analytical measurements. Both values must be positive numbers.
Q1: How do I determine the correct t-value?
A: The t-value depends on your desired confidence level (typically 99% for MDL) and degrees of freedom (n-1, where n is the number of replicates).
Q2: What's the difference between MDL and LOQ?
A: MDL is the minimum detectable concentration, while LOQ (Limit of Quantitation) is the minimum quantifiable concentration, typically 3-10 times higher than MDL.
Q3: How many replicates are needed for MDL determination?
A: Typically 7-10 replicates are analyzed to determine the standard deviation used in MDL calculation.
Q4: Does matrix affect MDL?
A: Yes, MDL should be determined in the same matrix as the samples being analyzed as matrix components can affect detection limits.
Q5: How often should MDL be verified?
A: MDL should be verified annually or whenever there are significant changes to the analytical method, instrument, or matrix.