Glossary: LOD and LOQ

LOD — limit of detection. The smallest quantity of a substance that an analytical method can reliably distinguish from nothing.

LOQ — limit of quantitation. The smallest quantity that the method can measure with a reportable degree of confidence. LOQ is always at or above LOD: detecting that something is present is an easier problem than measuring how much.

Why they appear on a Texas COA

25 TAC §300.301(d) requires that a certificate of analysis state the analytical methods and instrumentation used, together with limits of detection and limits of quantitation. They are among the twelve required fields.

Source: 25 TAC §300.301(d), adopted rules filed with the Secretary of State March 2, 2026 (TRD-202601066). In effect March 31, 2026.

What they are actually for

They give meaning to a negative result.

"Not detected" is not a statement about the world. It is a statement about an instrument. Without an LOD, it could mean:

• the substance is genuinely absent, or
• the substance is present at a level this method could not see

Those are very different facts, and the difference can matter. An LOD converts "not detected" into "not detected above this specific quantity", which is a claim a reader can evaluate.

LOQ does the same work for reported numbers. A figure reported below the limit of quantitation is not a measurement in the ordinary sense — it is below the level at which this method produces a value it can stand behind.

What to look for on a certificate

• Are LOD and LOQ stated at all? This is a common omission and it is a required field.
• Are they stated per analyte, or as a single blanket figure? Different substances have different detection characteristics.
• Is any reported result below the stated LOQ? If so, treat that number with the caution the laboratory's own limit implies.

Related terms

Measurement of uncertainty — the stated range around a reported result. Also a required field under §300.301(d), and closely related in purpose: both exist so that a single confident-looking number does not stand in for a range.

Accredited laboratory — §300.301(d) requires a QR code verifying the authenticity of testing at an accredited laboratory. LOD and LOQ figures derive their weight from the accreditation behind them.