“Not detected” is not proof of zero.

What the result establishes

EPA’s data-quality guide explains that a non-detect chemical concentration can lie between zero and the analytical detection limit. The result does not establish absolute absence.

Source: EPA QA/G-9R, section 4.7, page 52. This is environmental-data guidance, not a peptide-product specification.

Compare the limits

Illustrative example only: “not detected below 0.10 mg/L” and “not detected below 0.01 mg/L” do not have the same sensitivity. Neither means the concentration is zero.

A limit is not automatically an acceptance specification. Ask the laboratory which threshold the report uses.

Four questions to ask

• Which analyte was tested?
• What method and sample matrix were used?
• What limit and units apply?
• What specification, if any, was used for the decision?

Our editorial check: keep unlisted analytes unknown and avoid turning a single result into a universal safety conclusion.