How to Read a Chemical Technical Data Sheet

A tanker of glycerin arrives. Your QA lab runs it, the moisture comes back at 1.8% by Karl Fischer, and your downstream esterification stalls. You pull the supplier’s technical data sheet: it lists moisture as “0.5% typical.” You assumed that was the limit. It wasn’t. “Typical” is a representative number, not a guarantee, and the word does no work in a dispute. The lot was never out of spec, because you never contracted to a spec. You contracted to a brochure.

This is the most expensive mistake in chemical procurement, and it happens to experienced buyers. The technical data sheet (TDS) is the document you read first and trust most, yet it is the document with the least contractual force. Reading it well means knowing exactly what each number promises, which test method defines it, and where the gap between “typical” and “guaranteed” will cost you a rejected shipment you can’t return.

Key takeaways

• A TDS lists typical/representative values; a CoA lists actual lot results; an SDS covers safety. Contract to the CoA against an agreed spec, never to the TDS alone.
• Every parameter is meaningless without its test method. “Purity 99%” by GC area-% is not the same as 99% by titration; pin the method (ASTM/ISO/USP) in your PO.
• “Typical” ≠ “guaranteed.” Only values explicitly marked as specification, max, or min are enforceable limits. Treat everything else as marketing.
• Record the TDS revision number and date in the purchase order. Suppliers quietly re-issue data sheets; an unversioned reference lets the spec move under you.
• Check the basis on every number: wt% vs vol%, as-is vs dry basis, active vs total. A “98%” stated dry basis on a hydrated salt is a different product than 98% as-shipped.

TDS vs CoA vs SDS: which document actually binds the supplier?

The TDS binds nothing on its own. It is a representative profile of the product the supplier sells: typical assay, typical physical properties, packaging, shelf life. The Certificate of Analysis (CoA) is the lot-specific document that reports what your actual batch tested, against an agreed specification. The Safety Data Sheet (SDS) is a regulatory hazard document under GHS/HazCom and says nothing about whether the product meets your performance needs.

The trap is using the TDS as your spec. If your PO says “per supplier TDS,” you have agreed to typical values that the supplier never promised to hit on any given lot. The fix: lift the parameters that matter from the TDS, turn each into a guaranteed range with a named test method, and require a conforming CoA at every shipment. Your contract enforces the CoA-to-spec match, not the TDS.

For a deeper split on the safety side, see TDS vs SDS: key differences and uses in industry.

How do you read each TDS parameter and the test method behind it?

A number on a TDS is only as good as the method that produced it. The same property measured two ways gives two different answers, and a supplier who reports the more flattering method is not lying; they are letting you assume. Always read the parameter and the method as a pair, and carry both into your specification.

Match the grade to the method too. A “technical grade” and a “USP grade” of the same CAS can carry the same assay number against entirely different impurity panels. See the chemical grades guide for how grade designations change what the assay actually controls.

What is the difference between “typical” and “guaranteed” values?

Typical values describe the product the supplier usually makes. Guaranteed (or “spec,” “max,” “min”) values describe what the supplier will stand behind on every lot. Only the second kind is enforceable. A TDS often mixes both in the same column without flagging which is which, and the burden is on you to ask.

Read the header language carefully. “Typical Properties” or “Representative Analysis” at the top of a table means none of it is a spec. A column labeled “Specification” with “max”/”min” qualifiers is your enforceable boundary. When a parameter you depend on appears only as a typical value, send the supplier a one-line request: “Provide the guaranteed specification and test method for [parameter].” If they won’t commit to a max, treat that property as uncontrolled and plan your incoming inspection accordingly.

Why does the TDS revision number belong in your purchase order?

Suppliers revise data sheets (tightening a range, swapping a method, changing a typical value) and rarely announce it. If your PO references “the TDS” with no version, the document that defines your purchase can change between orders without your knowledge. The first you’ll hear of it is a lot that’s technically conforming to a spec you never saw.

Capture the revision number and issue date (e.g. “TDS Rev. 4, dated 2026-03-12”) in the PO or the quality specification annex. Require written notice of any TDS revision before it applies to your shipments. This is the same discipline you’d apply to a supplier audit: confirm the document of record hasn’t drifted. The chemical supplier audit checklist covers how to keep specification control across a supplier relationship.

How do unit and basis pitfalls void a clean-looking spec?

Two TDS numbers can both read “98%” and describe different products. The difference hides in the basis. Weight percent vs volume percent matters for liquids and blends: a “50% solution” by volume is not 50% by weight unless densities are equal, which they rarely are. Always confirm wt% vs vol%.

Dry basis vs as-is is the bigger trap for solids and hydrates. A salt reported “99% min, dry basis” can arrive at 95% as-shipped once you account for bound and free water — and still conform, because the basis excludes the moisture you’re paying freight on. Active content vs total content matters for diluted or stabilized products: a “70% active” hydrogen peroxide and a “70% solution” describe the same thing only by coincidence. Read every percentage with three questions: by weight or volume, on what basis, and active or total?

How do you turn a TDS into an RFQ and an incoming-inspection plan?

The TDS is your raw material for two documents that actually protect you: the RFQ and the inspection plan. Don’t ask the supplier to “match the TDS.” Extract the parameters that drive your process, convert each into a guaranteed range with a named method, and put those in the RFQ. The supplier now quotes against your spec, not their brochure, and the gaps surface before you place an order.

For the inspection plan, take the same parameter list and decide what you’ll verify at receipt versus what you’ll accept on the CoA. Critical parameters (the moisture that stalled your reaction, the trace metal that poisons your catalyst) get tested in-house on arrival. Less critical ones ride on a conforming CoA. Set the rejection trigger (CoA value outside spec), the notification window (typically 48–72 hours of arrival), and the right to third-party testing at the supplier’s cost when a CoA is disputed. The TDS told you what to expect; the inspection plan is how you prove you got it.

Frequently Asked Questions

What is a technical data sheet for chemicals?

A technical data sheet (TDS) is a supplier-issued document specifying a chemical’s typical composition, purity, physical properties, packaging, shelf life, and regulatory status. It describes the product the supplier usually makes and serves as the baseline for procurement qualification and for building your incoming specification. Read it before ordering. The CoA, by contrast, is reviewed at delivery to confirm a specific lot met the spec you contracted to. The TDS sets expectations; it does not, on its own, bind any individual shipment.

What is the difference between a TDS and an SDS?

A TDS specifies quality and performance — purity, grade, physical properties, packaging, shelf life — and is used to qualify and spec a product. An SDS (Safety Data Sheet) covers hazard identification, handling, PPE, and emergency response under GHS/HazCom. Both are required for industrial procurement but serve distinct functions: the TDS governs whether the material performs, the SDS governs how to handle it safely. An SDS never substitutes for a TDS or a CoA when you’re deciding whether a lot meets your specification.

What is the difference between a TDS and a CoA?

A TDS states typical, representative values the supplier commits to in advance. A CoA (Certificate of Analysis) is a lot-specific document issued at shipment reporting the actual test results for that batch against an agreed specification. Check the CoA against your spec at every delivery. A supplier cannot substitute a TDS for a CoA: the TDS tells you what the product should typically be; the CoA tells you what this particular lot actually is. Contract to the CoA-against-spec match, not to the TDS.

What should I check in a chemical TDS before placing a bulk order?

Verify the CAS number and grade designation; the purity/assay range with the specific test method cited (GC area-% vs titration are not equivalent); key impurity limits relevant to your application; moisture method (Karl Fischer vs loss-on-drying); packaging compatibility with your receiving infrastructure; shelf life and storage conditions; and regulatory status for your end-use market. Flag which values are “typical” versus “guaranteed,” and confirm the basis on every percentage (wt% vs vol%, dry vs as-is). Vague or typical-only entries are grounds for supplier clarification before committing container-load quantities.

Are TDS documents legally binding?

A TDS is a technical specification document, not a contract, and most of its values are typical rather than guaranteed. Enforceability depends entirely on how the TDS is incorporated into your purchase order, supply agreement, or quality specification annex. Reference the TDS version number and issue date explicitly in contract documentation, convert the parameters you depend on into guaranteed ranges with named test methods, and require that each CoA matches those ranges. That is what makes a deviation enforceable as a contract non-conformance.