What Is a Chemical Specification Sheet and How Do You Write One?

A chemical specification sheet is a document that states, in measurable terms, what your product is and what it must meet before you ship it. It is the contract between supplier and buyer: if a batch falls inside the limits it is on-spec and can be sold, and if it falls outside, it is off-spec. Buyers, customs agents and auditors all rely on it, and it also makes your internal quality control consistent from batch to batch.

How it differs from other documents

Four documents are often confused. The specification gives the limits that every batch must meet. The certificate of analysis (COA) reports the measured results for one particular batch against those limits. The technical data sheet (TDS) describes typical properties and applications to help a customer use the product. The safety data sheet (SDS) covers hazards, handling and emergency measures. The specification is the source of truth the COA is judged against. Our comparison of COA, SDS and TDS goes through the differences in detail.

What to include

• Product identity: product name, grade, CAS number and EC number, molecular formula and molecular weight, and any common synonyms. Check the identifier carefully, using our guide to CAS numbers.
• Appearance and form: colour, physical state (crystal, flake, powder, liquid), and odour where relevant.
• Assay: the minimum content of the active substance, with the test method, such as titration or HPLC.
• Impurity limits: maximum values for water or moisture, insoluble matter, chloride, sulphate, heavy metals such as lead and arsenic, iron, and any impurity specific to the application.
• Physical properties: density or specific gravity, pH of a stated solution, melting or boiling range, particle size, solubility.
• Test methods and standards: a reference for each parameter, which can be an ISO, ASTM or pharmacopoeia method, or an in-house method identified by number.
• Packaging and net weights: for instance 25 kg bags, 200 litre drums or 1 tonne IBCs, with materials of construction.
• Storage conditions and shelf life: temperature, humidity, light protection, and the period for which the specification is guaranteed.
• Regulatory status: REACH registration, food or pharma compliance statements, and other standards the product meets, only if they are true and documented.

Setting sensible limits

A common mistake is to write limits that are tighter than your process can reliably meet, which leads to constant off-spec batches, or looser than the buyer needs, which loses the sale. Base the limits on your historical batch data and on the customer's requirement, and express each as a minimum, a maximum or a range. Use realistic precision and make sure the test method can actually measure to that precision. Review the sheet whenever your process, raw material source or customer needs change.

Examples of specific limits

For a technical copper sulphate pentahydrate, a specification might state: appearance as blue crystals, copper content at least 25.0 percent, water insolubles at most 0.2 percent and a stated maximum for arsenic and lead. For 50 percent caustic soda liquor: NaOH at least 49 percent, sodium carbonate and chloride maximum values and iron maximum value. The exact figures depend on grade and application, which is why a buyer will usually share a requirement document first.

Version control and use

Give each specification a document number, a version and an issue date, and keep earlier versions on file, so you can show which limits applied to a past shipment. Link each batch COA to the specification version in force. Share the specification with sales and quality staff, and make sure customers get the current version only. For regulated markets, the product identity and composition on your specification must agree with Sections 1 and 3 of your SDS, so that your documents tell one consistent story. SDS Desk generates the SDS side of that set, and our SDS-writing guide shows how to build it.