01Detection and quantitation answer different questions

ICH Q2(R2) distinguishes the detection limit—the lower amount a procedure can detect—from the quantitation limit, where an amount can be measured with suitable accuracy and precision. Detecting a signal therefore does not necessarily mean the laboratory can assign it a reliable numerical concentration.ICH Q2(R2) (opens in a new tab)

The abbreviations vary: a laboratory may use DL or LOD for detection and QL or LOQ for quantitation. Read its definitions rather than assuming the letters on two certificates mean identical reporting rules. A method identifier alone may not tell you the applicable lower limit for the sample as tested.

02A sensitivity example

Suppose a hypothetical solvent test reports ND with a detection limit of 10 ppm. The defensible reading is that the solvent was not detected under that method's stated conditions. Writing “0 ppm” would claim an exact amount the report has not established.

Now suppose your research specification requires less than 1 ppm. An ND result from a procedure with a 10 ppm detection limit cannot, by itself, demonstrate that requirement. Values between 1 and 10 ppm illustrate the gap: they could matter to your criterion while lying below the method's stated detection capability. This example is about interpreting limits, not a result from a Novum certificate.

03A less-than result is not an exact measurement

The supplied water report lists bacterial endotoxins as <0.25 EU/mL against a stated limit of ≤0.25 EU/mL. Preserve the inequality when quoting the entry. It is neither an exact 0.25 EU/mL result nor a measured zero. The row does not, on its own, explain whether the reported boundary is the assay sensitivity or another reporting convention.Water report (PDF) (opens in a new tab)

This distinction matters when transferring results into spreadsheets. Entering 0, 0.25 or half the boundary creates an assumed numerical value. If a statistical analysis requires such a convention, it needs an explicit justification; for a simple certificate record, retain the original string and a separate field for the boundary and units.

04A reporting threshold is another separate detail

The supplied Semax chromatographic notes state a 0.05% reporting threshold. That note describes the report's treatment of chromatographic entries. It should not be renamed a universal detection limit for every possible impurity, and it does not establish the absence of substances that the method does not measure.Semax report (PDF) (opens in a new tab)

Similarly, a missing row is not an ND result. If an analyte is absent from the report, you do not know from that omission whether it was tested, excluded from the requested panel or recorded elsewhere. Ask directly rather than interpreting a short table as a comprehensive screen.

05What to ask the laboratory or supplier

• ✓What does ND mean in this specific report?
• ✓What are the detection and quantitation limits in the reported sample units?
• ✓Do dilution and sample preparation change the effective limit for the original material?
• ✓Does the method's scope cover the substance and sample type I need to assess?

The aim is a bounded conclusion: this analyte was not detected using this procedure at this stated sensitivity. That is useful evidence. Removing the method and limit makes the claim broader while making it less informative.