ANALYTICAL METHODS · PRACTICAL GUIDE
“Not Detected” Is Not Zero: Read Detection and Quantitation Limits
Learn what “not detected” tells you, and what number you still need.
A report says “not detected.” Can you write that the sample contains none of that substance? Not quite. Every method has a limit to what it can see and measure. The report needs to tell you that limit.
Seeing something and measuring it accurately are different
The detection limit concerns whether a low-level substance can be identified by the method. The quantitation limit concerns whether its amount can be measured with suitable performance. A faint signal may be recognizable before its quantity is reliable.
A reporting limit may be separately defined by the procedure. Ask which limit the report actually uses.
Follow one example from low to high
In this teaching example, the detection limit is about 0.2 µg/g and the quantitation limit is 0.6 µg/g. Below the detection capability, presence cannot be reliably established by these rules.
Above detection but below 0.6, there may be evidence of presence without a reliable numerical amount. In the established quantitative range, the method can support a quantity result.
Does the limit answer your requirement?
Suppose you require less than 0.1 µg/g, but the result only supports less than 0.2 µg/g. It does not settle whether the sample meets the stricter requirement.
Both numbers may look small. The gap between them still matters. Compare the same substance, units and sample basis.
A blank box is not “not detected”
A blank field may mean no result was supplied. “Not tested” means the test was not performed. “Not detected” describes an outcome under a method’s reporting rules. None automatically means an exact zero.
A displayed 0.000 can also be rounded or processed. Ask how it was generated before treating it as an exact value.
Ask one complete question
Ask: which substance was tested, by which method, in what units, and with what reporting limit? Endotoxin and residual solvent tests, for example, investigate different substances.
See the answer
No. The range from 0.5 to 1 µg/g has not been excluded.
Requesting results for LL-37 or GHK-Cu
For LL-37 or GHK-Cu, name the substance you want measured and the reporting capability you need. Confirm which tests were actually performed. HPLC purity does not provide an endotoxin result.
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BPC-157
KPV