Look up a reference standard by CAS number or formula

Why CAS numbers are the faster way in

A CAS Registry Number is assigned to one chemical substance and never reused, so it is the one identifier that survives every difference in naming convention. The same compound can appear as N-nitrosodimethylamine, NDMA, dimethylnitrosamine or N,N-dimethylnitrosoamine — four names, one CAS number.

Two practical quirks are worth knowing. First, the number is not a code: the final digit is a check digit computed from the preceding ones, so it carries no structural information and cannot be guessed. Second, a record can have more than one number when a substance was registered more than once, which is why a number that appears in a pharmacopoeia does not always match the number in a supplier catalogue.

If you only have the molecular formula, search that instead. A formula is less specific — every isomer shares it — so the lookup returns every catalogue entry with that composition and you pick the one whose structure matches. Enter it in any capitalisation; the search is case-insensitive and ignores spaces.

If the lookup returns nothing, the compound may still exist in the catalogue under a number we have not captured, or the number may belong to a salt or hydrate of a compound we list as the free base. Send it to us and we will check both cases against the physical inventory rather than the catalogue.

Many impurities have no CAS number at all, and never will: a number is only created once a substance has been described in the open literature, and most process and degradation impurities are characterised in-house and never published. Our guide to buying an impurity standard with no CAS number explains the four reasons it happens and the fields to send instead.