MDL vs LOQ: Which statement is true?

• A. MDL is the smallest concentration that can be quantified with acceptable accuracy and precision; LOQ is the smallest concentration that can be detected statistically.
• B. MDL is the largest concentration that can be detected; LOQ is the smallest concentration that can be measured with accuracy.
• C. MDL is the smallest concentration that can be statistically detected; LOQ is the smallest concentration that can be measured with acceptable accuracy and precision.
• D. MDL and LOQ are the same.

Answer: (C)

The main idea is the difference between detecting a substance and quantifying it. MDL (method detection limit) is about whether a concentration can be distinguished from blank with statistical confidence—that is, the smallest amount that can be detected. LOQ (limit of quantitation) is about whether that same concentration can be measured with acceptable accuracy and precision, the smallest amount you can quantify reliably. So the true statement says MDL is the smallest concentration that can be statistically detected, and LOQ is the smallest concentration that can be measured with acceptable accuracy and precision. In practice, LOQ is usually higher than MDL because being detectable is easier than being quantified accurately.