How many analyses must be completed to determine a minimum detection limit (MDL)?

To determine a Minimum Detection Limit (MDL), seven independent analyses are required based on established protocols and guidelines, such as those provided by the U.S. Environmental Protection Agency (EPA). This quantity is necessary to ensure that the MDL is reliable and statistically valid.

Conducting seven analyses allows for adequate statistical treatment of the data, which helps to account for variability in measurements and provides a robust basis for calculating the MDL. Specifically, the process involves taking the standard deviation of the measurements and using it in conjunction with the average of those measurements to determine the MDL accurately.

Using fewer analyses, such as five, would not provide enough data points to achieve the level of statistical integrity needed in results, while conducting more than seven, like ten or twelve, is typically unnecessary and not specified in standard methods for establishing an MDL. Thus, seven analyses strikes a balance between ensuring quality data collection and practical lab operations.