A symbol carries part of the result

A laboratory table containing <5 is not reporting the same information as a table containing 0. The less-than sign is part of the observation. Copying the number into a spreadsheet while dropping that sign can quietly turn a limited measurement into an exact claim.

Why a procedure has a working range

IUPAC defines a quantification limit by whether a measurement procedure meets a specified fitness requirement. Such a requirement may concern repeatability or uncertainty. Lower and upper limits bound the working interval. Detecting something and quantifying it acceptably are separate capabilities; the detection limit should not be confused with the bottom of the working interval.

An original example with two reports

Suppose two hypothetical reports for an unnamed constituent state <5 micrograms per litre and <20 micrograms per litre. These are illustrative reporting limits, not product results. The first gives a tighter upper boundary. It does not prove that its sample contains less material than the second: both could contain an amount below 5, and neither entry supplies an exact concentration.

Changing units does not remove that uncertainty. Because one milligram equals 1,000 micrograms, <5 micrograms per litre becomes <0.005 milligrams per litre. The inequality travels with the conversion. Writing 0.005 as though it were the measured value would be a different error from writing zero, but both would discard the original meaning.

Keep the method beside the number

For a useful comparison, retain the constituent, units, result qualifier and stated reporting limit. Ask whether the limit refers to detection, quantification or another reporting rule. A bare phrase such as not detected needs that context before it can support a claim about composition.

The same care matters when reading a blend: an unquantified constituent is not automatically an absent constituent, and an omitted test is not a zero result. Arithmetic cannot fill in a missing assay. Keep unknown values visibly unknown rather than allowing a spreadsheet default to decide their meaning.

Definitions and an illustration, not a preparation guide

The full official indexed IUPAC entries were reviewed in the 2025 online edition. Their underlying recommendations date to 2021. The examples above are original S7 arithmetic for reading reports; they do not establish any product's identity, purity, sterility or suitability for use, and contain no preparation or administration instructions.