COA, TDS and SDS: what each document actually proves

Buyers often treat the certificate of analysis, the technical data sheet and the safety data sheet as three versions of the same paperwork. They answer three different questions, and mixing them up is how specification disputes start.

Certificate of analysis: what this batch measured

A COA is a batch record. It should name the product, the batch or lot number, the test items, the specification limits, the measured result for each item, the test methods used, and a date with a signature or stamp.

What it proves: the values recorded for the batch you were shipped. What it does not prove: that the sample tested is the material in your drum, or that the material is what the label says. A COA is a claim made by the seller, not an independent finding.

Read it for internal consistency first. A result outside the stated limit that still passes is a typo at best. A COA with no batch number cannot be tied to anything.

Technical data sheet: what the product is designed to be

The TDS describes the product as a commercial grade. Typical items are appearance, assay or purity, density, melting or boiling range, solubility, recommended applications and storage conditions.

What it proves: the manufacturer's intended specification and the range they normally supply. What it does not prove: anything about the drum in front of you. TDS values are often typical values, not guaranteed limits, and typical means the average of past production.

If a specification matters to your process, it has to appear as a guaranteed limit in the contract, not only as a typical value on a TDS.

Safety data sheet: how to handle it, not how good it is

An SDS is a hazard communication document with 16 sections covering identification, hazards, composition, first aid, firefighting, handling, exposure controls, transport and regulatory information.

What it proves: the hazards the supplier is declaring, and the transport classification. What it does not prove: quality, purity, or suitability for your application. Two suppliers can ship the same grade with very different SDS quality.

One practical check: section 3 composition and section 9 physical properties should be consistent with the TDS. If the SDS lists a purity range that contradicts the TDS, ask which one is contractually binding.

Where the three fit together

Use the TDS to decide whether the grade is right, the SDS to decide whether you can handle and ship it, and the COA to check what arrived. They are three stages of one decision, not substitutes for each other.

Questions that expose a weak COA

• Which laboratory ran the test, in-house or third party?
• What method was used for the assay, and is it the same method as the specification?
• Can you send the COA for the batch that is being loaded, not the previous one?
• What is the retest or shelf life date, and what happens if the material arrives after it?