Documentation Guide
COA, SDS and Specification: Three Documents, Three Questions
A certificate reports what one batch measured, a specification what material must meet, a safety data sheet hazard. Three documents, three different questions.
[Research Use Only] This guide is for controlled laboratory research workflows only. It is not for human or veterinary use and does not provide applied-use guidance.
Three documents, routinely conflated
Ask for the paperwork on a research chemical and three different documents may arrive, any one of which might be offered as though it settled the question of quality. They do not answer the same question, they are not produced at the same point in the process, and two of the three contain no analytical findings at all. Knowing which document answers which question is the difference between reading evidence and reading reassurance.
The certificate of analysis
A certificate of analysis is a batch-specific analytical document. It connects an identified quantity of material to results obtained from testing a sample of it, on a stated date, by stated or referenced methods. Its authority comes entirely from that connection: remove the batch identifier and the results describe nothing in particular.
- Identifies a specific batch or lot, and should match the label on the material
- States which tests were performed, not merely that testing occurred
- Reports the result obtained for each test
- Names or references the analytical procedure used
- Carries a date, which fixes the results to a moment rather than to the present
What a certificate cannot establish
A certificate is evidence about the attributes it reports, in the sample analysed, at the time of analysis. It is silent on everything else. It cannot speak to attributes that were not tested, and it cannot speak to what has happened to the material since — handling, storage and elapsed time all sit outside the document entirely. A certificate is not a warranty about the vial in front of you; it is a record of a measurement made upstream of it.
- Says nothing about attributes it does not list
- Describes the sample analysed, which is not the same as every unit in the batch
- Cannot account for storage or handling after the analysis date
- Does not establish that the material is suitable for any particular purpose
The specification
A specification is the standard the material is measured against. ICH Q6A defines it as a list of tests, references to analytical procedures, and appropriate acceptance criteria — numerical limits, ranges, or other criteria for the tests described — establishing the set of criteria to which a substance or product should conform to be considered acceptable for its intended use. It is written in advance, and it is general: it describes a product, not a batch.
Why a specification is not a certificate
The distinction is not pedantry, because a specification can legitimately list tests that are not run on every batch. Q6A describes periodic or skip testing as the performance of specified tests at release on pre-selected batches, or at predetermined intervals, rather than on a batch-to-batch basis — while batches not tested must still meet all acceptance criteria established for that product. A specification therefore tells you the standard in force. Only the certificate tells you what was actually measured for the batch you hold.
- A specification exists before any batch is made; a certificate cannot
- A specification states thresholds; a certificate states findings
- A specification may include tests not performed on every batch
- Conformance is a conclusion drawn from a certificate, not a property of the specification
The safety data sheet
A safety data sheet is a hazard communication document, and it belongs to a different regulatory world from the other two. In Great Britain the requirement sits under UK REACH, and HSE describes safety data sheets as important documents in the safe supply, handling and use of chemicals, supplied where a chemical is hazardous and is being supplied for use at work. Its structure is prescribed: Annex II sets out sixteen headings, from identification of the substance through to regulatory information.
- Concerns hazard, exposure, response and disposal
- Describes the substance or mixture as supplied, not a particular batch
- Follows a prescribed sixteen-section structure
- Is supplied by the supplier, in advance of and independent of any analysis
Why an SDS is not evidence of purity
This is the most consequential of the three confusions, because a safety data sheet looks technical, carries regulatory weight, and is often the longest document in the set. None of that makes it analytical evidence. It reports no measured result for the material you hold, it is not written against a batch, and it does not change when a batch is tested. HSE is explicit about a related limit that points the same way: the SDS itself is not an assessment. It is an input to judgement, not the judgement — and certainly not a measurement.
The three side by side
The table below is arranged with the questions down the side rather than across the top, because the useful comparison is what each document says in answer to the same question — and because the answers are frequently the opposite of what readers assume.
| Certificate of Analysis | Specification | Safety Data Sheet | |
|---|---|---|---|
| Purpose | Report what a batch was measured to be | Define what material must meet to be acceptable | Communicate hazard and precautionary information |
| Applies to | One identified batch or lot | A product or substance in general | A substance or mixture as supplied |
| Typical contents | Tests performed, results, method references, batch identity, date | Tests, references to analytical procedures, acceptance criteria | Sixteen prescribed sections, identification through regulatory information |
| Batch-specific? | Yes — this is the point of it | No — written before any batch exists | No — describes the substance, not a batch |
| Contains analytical findings? | Yes, for the tests it reports | No — criteria, not results | No |
| Contains hazard information? | No | No | Yes — this is its entire purpose |
| Produced when? | After a batch is tested | Before any batch is produced | Before supply, independent of testing |
| What it cannot tell you | Whether untested attributes conform, or the state of the material now | What any particular batch actually measured | Anything about purity, identity or analytical quality |
How the documents relate in sequence
Placing them in order makes clear why substituting one for another does not work: they are produced at different points, and only one of them sits downstream of a measurement.
- Specification setTests, procedures and acceptance criteria are defined in advance of any batch.
- Batch producedMaterial is manufactured and assigned an identifier that will follow it.
- Sample analysedListed procedures are run against a sample drawn from that batch.
- Certificate issuedResults are reported against the batch identifier and the date of analysis.
- Conformance judgedReported results are compared against the acceptance criteria in the specification.
Reading a set of documents together
When all three are available, the questions worth asking are about whether they actually refer to one another. A certificate that names no method cannot be checked against a specification. A specification with no certificate is an unevidenced promise. A safety data sheet offered in place of either is answering a question nobody asked.
- Does the certificate name a batch, and does that batch appear on the material?
- Does the certificate name the procedures, or only the outcomes?
- Are the acceptance criteria stated anywhere, or only the results?
- Is the analysis date present, and how long ago was it?
- Is a safety data sheet being offered as evidence of something it does not measure?
Research Checklist
- Confirm batch identity and records.
- Document all preparation inputs.
- Keep use within controlled laboratory workflows.
- Do not infer applied-use suitability from guide content.
Frequently Asked Questions
If a supplier provides a safety data sheet, does that indicate the material was tested?
No. A safety data sheet is a hazard communication document produced for the substance as supplied. It is not generated by analysis, is not written against a batch, and does not change as a result of testing. Its presence indicates that hazard information has been communicated, which is a separate matter from whether analytical testing was performed.
Is a specification stronger evidence than a certificate, since it is the standard?
They are not on the same axis. A specification states what material must meet; a certificate states what a batch reported. A specification alone establishes an intention and a threshold, with no finding attached. Conformance is a conclusion you can only reach by reading a certificate against a specification.
Does a certificate mean every unit in the batch meets the result shown?
A certificate reports results from the sample or samples analysed. Whether those results represent the whole batch depends on sampling and on how homogeneous the material is. The certificate reports a measurement; treating it as a per-unit guarantee reads more into the document than it states.
Why might a specification list a test that does not appear on the certificate?
Legitimately, because not every listed test is necessarily performed on every batch. ICH Q6A describes periodic or skip testing, where specified tests are performed on pre-selected batches or at intervals rather than batch by batch, while batches not tested must still meet all acceptance criteria. Where that applies in a regulated setting, it is something that has to be justified and approved rather than simply adopted.
Sources
The technical statements in this guide are drawn from the following. Where a definition is contested or a figure depends on method, the guide says so rather than picking one.
- ICH Q6A: Specifications — Test Procedures and Acceptance Criteria for New Drug Substances and New Drug Products: Chemical SubstancesInternational Council for HarmonisationUsed for the definition of a specification, the meaning of conformance to specifications, and the description of periodic or skip testing.
- Safety data sheetsHealth and Safety ExecutiveUsed for the purpose of a safety data sheet, when one must be supplied, and the statement that the safety data sheet is not itself an assessment.
- REACH Annex II: Requirements for the compilation of safety data sheetsRegulation (EC) No 1907/2006, via legislation.gov.ukUsed for the prescribed sixteen-section structure of a safety data sheet.