A laboratory report may mention a “blank”, “method blank” or a blank-related qualifier beside a result. Before deciding what that note means, ask what was tested without the sample, which part of the work it checked, and how the laboratory assessed the finding. The word “blank” alone does not answer those questions.
This guide is about reading that supporting information. It is not a procedure for running tests or a rule for accepting a particular result.
Start with the type of blank
In Eurachem’s 2025 guide to blanks, a procedural blank goes through the full analytical procedure without the sample matrix. It helps assess contamination or interference introduced during that work. Reports may use “method blank” for a related control; ask which definition the laboratory uses.
A reagent blank contains the relevant reagents or solvents without the sample matrix. A solvent blank checks the solvent presented to the instrument. When measured after a calibration standard or another suitable material, a solvent blank can also help reveal carryover: a contribution left from a preceding measurement.
A sample or matrix blank contains representative matrix with no detectable target substance, or a very low, known amount. It can reveal interference that a solvent-only control cannot represent. For context, see why methods and sample matrices matter when comparing results.
Read the flag before judging the sample
A useful first request is: “Please explain this qualifier in relation to this result.” Keep the question tied to the named substance, sample identifier and report version. A general explanation of blanks may be informative while leaving your particular report unresolved.
The US EPA’s guidance for fish and shellfish analysis explains that contamination in a blank does not automatically establish contamination in the associated samples. Interpretation requires the applicable method and professional assessment. It also cautions against subtracting a blank value from a reported sample result unless the method explicitly requires that approach. These are US environmental-analysis examples, not EU cannabinoid legal requirements.
For a reader, the practical lesson is to request the laboratory’s documented interpretation rather than make a correction independently. Ask whether the flag changes the reported value, its qualification, or the laboratory’s conclusion about whether the result is usable. Keep those questions separate from what a detection or quantification limit means; our guide to detection versus quantification covers that distinction.
Which part of the journey was checked?
Blank names can refer to different stages outside the main analytical procedure. The EPA’s archived overview of blank types distinguishes field, trip, equipment and instrument blanks. A field blank encounters field conditions; a trip blank remains closed during its journey. Equipment and instrument blanks examine different possible routes of contamination. These US environmental-analysis examples illustrate why the control’s scope matters, rather than prescribing controls for every laboratory report.
When asking about a certificate of analysis, avoid requesting every possible blank by name. A more focused question is: “Which controls were relevant to this test, and what part of the work did each cover?” That leaves room for the laboratory to explain its actual method instead of treating an unrelated checklist as a requirement.
A hypothetical report-reading example
Imagine a report lists substance A and adds “blank-related qualifier”. No blank result or explanation accompanies it. A reader might be tempted either to dismiss the whole report or to ignore the note. Neither choice resolves the missing information.
A focused enquiry would identify the sample and ask which blank triggered the note, whether it concerned substance A, and which acceptance criteria were applied. Then ask for the assessment of the associated sample result. This hypothetical example supplies no numerical acceptance rule: that answer belongs with the laboratory’s method and review.
Questions worth keeping with the report
- What does this laboratory mean by the named blank?
- Which preparation batch or measurement sequence does it relate to?
- What was observed, and where is that information recorded?
- Which criteria were used to assess the finding?
- Was the sample result qualified, investigated or reanalysed?
- Does the explanation require an updated report?
If a replacement is issued, retain the explanation and check the identifiers using our guide to revised laboratory report versions. The goal is a clear record of what the blank checked, what was found and how the laboratory addressed it.
Reviewed: 28 October 2026.