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CAS number (chemical identifier)
A unique numeric identifier such as “7732-18-5” (water) assigned to each chemical substance by the Chemical Abstracts Service of the American Chemical Society. Because the same substance can be sold under many trade and local names, it is the most reliable way to avoid confusion in sourcing; SDSs, REACH registrations, customs and restricted-substance lists all work by CAS number. Mixtures have no single CAS number – their components are listed separately. In the EU the EC (EINECS) number is also used.
Chemical purity grades (technical, food, pharma, analytical)
The same chemical is sold in different purity and impurity limits at different prices. Technical or industrial grade is for general manufacturing; food grade (E-number additives, FCC or JECFA specifications, heavy-metal limits) for food and feed; pharmacopoeia grade (USP, EP/Ph. Eur., BP, JP) for medicines and some cosmetics, produced under GMP; analytical or reagent grade (ACS, AR, HPLC) for laboratories. Using a lower grade in place of a higher one breaches regulations, so the grade and reference specification must be written on the order and the COA.