What is a CAS?
CAS numbers are unique identifiers assigned to chemical substances. Each CAS number consists of three parts separated by hyphens, for example 64175 (ethanol). The format follows the pattern xxxxxxxxx, where the final digit is a check digit automatically generated from the preceding numbers.
Why Use Multiple CAS Values?
In scientific databases, product catalogs, and regulatory filings a single item may be related to several chemicals. Storing each chemical in a separate field quickly becomes impractical, especially when the number of associated substances varies from record to record. A common solution is to keep them in a single text field, separated by commas the multiple CAS (commadelimited) format.
Advantages of this approach include:
- Simple schema only one column is needed.
- Easy to export to CSV, Excel or flatfile systems.
- Humanreadable without special tools.
However, it also introduces challenges for searching, validation, and data integrity, which we discuss below.
Common Use Cases
Product Ingredient Lists
A cleaning product may contain several active ingredients, each identified by its own CAS. A typical entry could look like:
58082, 67561, 64197
Regulatory Reporting
When filing under REACH or TSCA, a manufacturer must list all substances present above a certain threshold. Using a commadelimited list keeps the submission concise.
Scientific Data Sets
Research repositories often store assay results where a sample was exposed to a mixture of chemicals. The CAS field holds the mixture composition.
Parsing and Validation Techniques
Because a commadelimited string is essentially freeform text, it must be parsed before any meaningful operation.
Basic Splitting
In most programming languages a simple split(',') will separate values. Trim whitespace after splitting:
let raw = "58082, 67561 ,64197";let parts = raw.split(',').map(s => s.trim());// parts => ["58082","67561","64197"]RegularExpression Validation
To ensure each token conforms to the CAS pattern, use a regex such as:
^\d{2,7}-\d{2}-\d$Apply it to every split token. If any token fails, flag the record for correction.
CheckDigit Verification
The last digit of a CAS number is a check digit. Verify it with the following algorithm:
// pseudocodefunction isValidCAS(cas) { let parts = cas.split('-'); if (parts.length !== 3) return false; let digits = (parts[0] + parts[1]).split('').reverse(); let sum = 0; for (let i=0; iDatabase Design Considerations
While commadelimited fields are convenient for quick data entry, relational databases work best with normalized structures.
Normalized Model
Create a junction table that links a primary entity (e.g., Product) to individual CAS entries:
Product---------product_id (PK)name...ProductCAS---------product_id (FK)cas_number (PK)This approach enables efficient indexing, searching, and referential integrity. It does, however, increase schema complexity.
When to Keep a Delimited Column
- Data is readonly or rarely queried by individual CAS.
- Exportoriented workflows dominate the use case.
- Legacy systems already rely on the format.
In such scenarios, store the delimited list but also keep a derived searchable column where each CAS is stored as a separate token (e.g., using a fulltext index or a JSON array).
Search Strategies
Searching for a specific CAS inside a delimited string can be slower than a normalized lookup. Common techniques include:
- LIKE queries with delimiters:
WHERE cas_list LIKE '%,67561,%'(add leading/trailing commas to avoid partial matches). - Fulltext indexes on the column (supported by MySQL, PostgreSQL, etc.).
- JSON or array fields in modern DBMS (PostgreSQL
jsonb_array_elements_textor MySQLJSON_CONTAINS).
For highperformance applications, migrate to a junction table whenever possible.
Best Practices Checklist
- Validate format and checkdigit for every CAS token.
- Trim whitespace and remove empty entries after splitting.
- Store CAS numbers in uppercase and use the hyphenated form consistently.
- If the data will be queried often, consider a normalized relationship table.
- Document any exception handling (e.g., CAS not assigned placeholders).
- When exporting, ensure the same delimiter (comma) and character encoding (UTF8).
