Reading a Chemical Specification: CAS Numbers, Grades and What to Ask

Most sourcing problems start with a specification that was never properly written down. This note sets out the fields worth checking on a chemical specification and the questions that avoid a rejected delivery.

Start with the CAS number

A CAS Registry Number identifies a chemical substance — not a grade, not a purity, not a supplier’s product code. Two suppliers quoting “the same” CAS number can still be offering materially different products.

It is also worth remembering what a CAS number does not tell you:

• It does not specify assay or impurity limits.
• It does not distinguish physical form — powder, granule, flake or solution usually share one CAS number.
• It does not distinguish hydrate state. Anhydrous and heptahydrate forms of the same salt have different CAS numbers and different uses.
• For polymers and natural extracts, a CAS number may refer to a family rather than a single defined substance.

Grade is the second filter

The same commodity is often traded in several grades, and the grade determines what documentation and compliance trail you can expect:

• Technical / industrial grade — for process use where food contact is not involved.
• Food grade — meets a recognised food-chemical monograph (for example FCC, E-number, BP or USP where applicable).
• Feed grade — intended for animal feed; suppliers are often certified to a feed-safety scheme.
• Pharmaceutical grade — meets a pharmacopoeia monograph and comes with a corresponding compliance pack.

Always confirm the grade in writing. “Industrial grade” substituted for a food-grade requirement is a recall risk, not a cost saving.

The specification fields worth checking

• Assay / active content — and how it is expressed (as-is, dry basis, or as an oxide equivalent).
• Moisture — affects both dosing and shelf life.
• Heavy metals — lead, arsenic, cadmium and mercury limits matter for food and feed applications.
• Insolubles and clarity — critical for solution products and for anything dosed through a fine filter.
• Particle size distribution — a coarse granule and a fine powder can behave very differently in a blender or a feeder.
• Packaging format — 25 kg bag, 1,000 kg jumbo bag, drum or IBC; confirm the net weight and the pallet configuration.

Documents to request before ordering

1. COA — Certificate of Analysis for the actual batch you will receive, not a generic sample certificate.
2. TDS — Technical Data Sheet covering typical properties, packaging and storage.
3. SDS — Safety Data Sheet in the format required in your jurisdiction.
4. Certificates, where the application demands them — for example halal or kosher declarations for food ingredients.

Questions that prevent rework

• Is the quoted price for the assay I specified, or for a lower-content grade?
• Which physical form is being offered, and can it be handled by my existing equipment?
• What is the batch size and the lead time for a repeat order?
• Can the product be re-packed into our own packaging, and under our own label?
• What is the shelf life, and how should it be stored in a tropical climate?

In short

Write the specification first, then buy. A precise specification — CAS number, grade, assay, form, packaging and the documents required — is the cheapest form of quality control you will ever put in place.