CASRN or CAS Registry Number®
This is a unique numerical identifier created and assigned to a chemical substance by CAS (Chemical Abstract Society).
A CAS registry number is separated by hyphens into three parts, the first consisting of up to 6 digits, the second consisting of two digits, and the third consisting of a single digit serving as a check digit. The numbers are assigned in increasing order and do not have any inherent meaning. The checksum is calculated by taking the last digit times 1, the next digit times 2, the next digit times 3 etc., adding all these up and computing the sum modulo 10.

EINECS, ELINC and NLP
The EINECS number (for European Inventory of Existing Chemical Substances) is a registry number given to each chemical substance commercially available in the European Union between 1 January 1971 and 18 September 1981. The inventory was created by Directive 67/548/EEC concerning the labeling of dangerous substances: the EINECS number(s) must appear on the label and the packaging of dangerous substances.

Within the scheme of the notification of new substances (Directive 67/548/EEC) polymers are subject to special rules. The term polymer was further defined in the 7th amendment (92/32/EEC) of the Directive. This change means that some substances which were considered to be polymers under the reporting rules when the European Inventory of Existing Commercial Chemical Substances (EINECS) was being established are no longer considered to be polymers under the 7th amendment.

Polymers were not reportable for EINECS. As all substances which are not present in the EINECS inventory are notifiable, all "no-longer polymers (NLP)" should in theory be notified.

However, at the time when the 7th amendment was adopted, the Council of Ministers made it clear that these no-longer polymers should not, retrospectively, become subject to notification. To facilitate the work of national Competent Authorities and the industry the Commission was requested to draw up a list of no-longer polymers.

Substances to be included in this list have been on the EU market between September 18, 1981, and October 31, 1993 and satisfy the requirement that they were considered to be polymers under the reporting rules for EINECS but are no longer considered to be polymers under the 7th amendment. Therefore to create the no-longer polymer list industry was asked to submit their candidates.

The term EC number is now preferred to the outmoded "EINECS/ELINCS/NLP number" designations, but this is not to be confused with the Enzyme Commission EC numbers.

Beilstein Registry Number (BRN)
The Beilstein Registry Number (BRN) is assigned when a compound is registered for the first time in the Beilstein Information System. In general the registration procedure is based on the available structural information for a substance, which is included in the connection table. Exceptions are biomolecules, mixtures and polymers. Both the BRN and the structure of a substance are unambiguous identifiers of substances. The Beilstein Registry Number is the accession number of the substance record in Cross Fire and in the Beilstein Online database. It is an integer, which does not contain further information.

Oil and Hazardous Materials/Technical Assistance Data System (OHMTADS)
OHMTADS provides access to a data file created by the Superfund program of the US Environmental Protection Agency to aid emergency response teams in the rapid retrieval of chemical-specific response information.

Registry of Toxic Effects of Chemical Substances (RTECS®)
The RTECS® Database is compiled, maintained, and updated by MDL Information Systems, Inc., under the authority of the U.S. government. Toxicity information and other data such as chemical identifiers used in the preparation of safety directives and hazard evaluations is available for over 162,100 chemicals and substances.