CAS (Chemical Abstracts Service)

What is CAS Number?

CAS stands for Chemical Abstracts Service, a division of the American Chemical Society. It operates the CAS Registry, which assigns a unique identifier (CAS Registry Number, or CAS RN) to every chemical substance disclosed in scientific literature. These identifiers are used globally to unambiguously identify molecules, compounds, polymers, biological sequences, and other materials.

Why is CAS Important in Pharma?

In the pharmaceutical industry, CAS numbers are essential for:

• Ensuring precise substance identification of APIs, excipients, intermediates, or impurities across different databases and regulatory documents.
• Avoiding confusion due to multiple names, synonyms, trade names, or common vs systematic names.
• Supporting regulatory submissions, pharmacopoeial references, safety documentation like SDS/MSDS, and tracking in supply chains.
• Ensuring global regulatory and commercial stakeholders are referring to the same substance.

Core Principles of CAS / Key Attributes

• Uniqueness: Each CAS RN corresponds to exactly one chemical substance or exact molecular entity. No two distinct substances share the same CAS number.
• Standard Format: A CAS number consists of three parts separated by hyphens: first part (2 to 7 digits), second part (2 digits), and the final check digit (one digit) used for validation. Example: water is 7732‑18‑5.
• Sequential Assignment: Numbers are assigned in sequence as new substances are added to the CAS Registry; CAS numbers do not encode structural or chemical property information themselves.
• Global Recognition & Regulatory Reliance: CAS RN is accepted by regulatory agencies globally as a substance identifier in laws, safety, import/export documentation, and trade compliance.

How CAS Works in Practice (Pharma Context)

1. Substance Publication / Disclosure: When a chemical substance is first disclosed in scientific literature, patent filing, or other recognized report, it becomes eligible for registration in the CAS Registry. CAS scientists validate and index the substance.
2. Registration & Number Assignment: CAS assigns a unique CAS Registry Number (CAS RN) to the substance. This CAS RN is then used in databases, regulatory documents, safety data sheets, and supply chain systems.
3. Use in Regulatory/Pharma Documents: Pharma manufacturers include the CAS RN in product specifications, COA (Certificate of Analysis), SDS/MSDS, pharmacopoeial monographs, labeling, regulatory submissions (eg, NDA, ANDA, API registrations), etc., so that there is no ambiguity about the chemical identity.
4. Database / Discovery / Literature Searches: Researchers, quality control labs, regulators, and procurement teams use the CAS RN to search literature, safety information, prior art, supplier catalogs, and regulatory databases reliably.
5. Verification & Validation: Because CAS RN includes a check digit, there is built‑in error detection. Also, external parties can verify the CAS RN via authoritative sources (CAS website, CAS Common Chemistry, etc.) to ensure the substance is correctly identified.

Real‑World Examples in Pharmaceutical Supply Chains

• A supplier of APIs on Pharmint includes CAS RN in the product listing to allow buyers and regulatory agencies to verify the identity of the active pharmaceutical ingredient unambiguously.
• A pharmaceutical formulation uses multiple excipients; in documentation (COA, SDS), each excipient is referenced with its CAS number so QC labs can cross‑check purity, safety limits, and regulatory compliance.
• During a pharmacopoeial monograph update, a manufacturer reviews all CAS numbers referenced in the document to ensure their registered substances are correctly matched, avoiding mismatches or misidentification.

Related Terms and Concepts

• Pharmacopeial Compliance — monographs often reference CAS numbers to identify APIs, excipients, or impurities.
• Certificate of Analysis (COA) — COA often includes CAS RNs for substances tested.
• Active Pharmaceutical Ingredient (API) — APIs have CAS numbers.
• Impurity Profile — Impurities are identified by CAS RN for regulatory reporting.
• Safety Data Sheet (SDS) / Material Safety Data Sheet (MSDS) — CAS RN is a required field in SDS under GHS.

CAS Number FAQs

What exactly does a CAS number represent?

A CAS Number represents a unique identifier assigned by Chemical Abstracts Service to a specific chemical substance, helping avoid ambiguity with common or trade names.

How is the check digit in a CAS number calculated?

The check digit is derived by multiplying each digit of the preceding parts (from right to left) by sequential multipliers (1,2,3…), summing results, then computing the modulus 10 of the sum.

Can one chemical have multiple CAS numbers?

No, each distinct chemical entity has exactly one CAS RN. Isomers, different mixture forms, or distinct molecular species get different CAS RNs.

Do CAS numbers convey chemical structure or property?

No, the CAS RN itself has no chemical structural meaning; it purely serves as an identifier. Structure or property details must be found via registry lookup or databases.

Where can I verify or find a CAS number for a substance?

Use the CAS Registry (via CAS website), CAS Common Chemistry, or trusted regulatory/scientific databases. QA/QC labs also refer to SDS, COA, or supplier documentation.

Are CAS numbers required in Safety Data Sheets (SDS)?

Yes, under GHS (Globally Harmonized System) safety regulations, SDS must include CAS numbers in the ingredients section to clearly identify chemical substances.

How are CAS numbers used in regulatory submissions?

CAS RNs are used in APIs, excipient identity documentation, impurity profiling, chemical registration (e.g., REACH, US EPA), pharmacopoeial monographs, and product labeling to ensure precise substance identification.

What if I have the wrong CAS number for my substance?

Using an incorrect CAS RN can lead to misidentification of substance, regulatory non‑compliance, safety or quality risks, trade documentation errors, or rejection of regulatory filings.

Can proprietary or trade‑named chemicals share a CAS RN?

No, trade names or proprietary names are not unique; only the chemical substance gets one CAS RN. Multiple commercial trade names may reference the same CAS RN if referring to the identical chemical entity.

Does CAS number assignment cost anything / how long does it take?

Assignment of a CAS RN for novel or less-known substances may involve a process via CAS Registry Services. Accessing certain detailed registry data or services may require subscription/licensing; timing depends on substance disclosure and indexing.