Every chemical compound has a CAS Registry Number — a unique identifier assigned by the Chemical Abstracts Service (CAS), a division of the American Chemical Society. For procurement teams sourcing industrial chemicals, CAS numbers are the single most reliable way to specify exactly what you need, prevent substitutions, and maintain a consistent supply chain.
What is a CAS Number?
A CAS number follows the format XXXXXX-YY-Z, where:
- The first segment is a variable-length number (up to 7 digits)
- The second segment is always 2 digits
- The third segment is a single check digit, calculated algorithmically from the preceding digits
Example: Acetone = 67-64-1. The "1" is a check digit. No two chemicals share the same CAS number — isomers (same molecular formula, different structure) get different numbers. Toluene (C₇H₈, CAS 108-88-3) and ortho-xylene (C₈H₁₀, CAS 95-47-6) are distinct entries.
Why CAS Numbers Matter in Procurement
1. Eliminate ambiguity in specification. "Xylene" in a purchase order could mean ortho-xylene, meta-xylene, para-xylene, or mixed xylene — four different products with different properties. "Propylene glycol" without a CAS number leaves open whether you want mono-propylene glycol (CAS 57-55-6) or di-propylene glycol (CAS 25265-71-8). The CAS number removes all ambiguity.
2. Cross-reference suppliers. Different suppliers use different trade names for the same chemical. "MIBK", "methyl isobutyl ketone", and "4-methyl-2-pentanone" are the same substance (CAS 108-10-1). A CAS number lets you accurately compare quotes across suppliers.
3. Regulatory and documentation compliance. Safety Data Sheets (SDS) are keyed to CAS numbers. Import documentation, customs HS code classification, and environmental permits frequently require them. Without a CAS number, your SDS may not match your purchase.
4. Prevent substitution risk. Without a CAS number on the purchase order, a supplier could deliver a similar but not identical product — particularly common with "equivalent" grades or technical substitutes. The CAS number creates a clear contractual specification.
Commonly Confused Pairs (CAS Numbers)
| Chemical 1 | CAS | Chemical 2 | CAS |
|---|---|---|---|
| Ethyl Acetate | 141-78-6 | Butyl Acetate | 123-86-4 |
| MEK (Methyl Ethyl Ketone) | 78-93-3 | MIBK (Methyl Isobutyl Ketone) | 108-10-1 |
| IPA (Isopropyl Alcohol) | 67-63-0 | n-Propanol | 71-23-8 |
| DEG (Diethylene Glycol) | 111-46-6 | MEG (Monoethylene Glycol) | 107-21-1 |
| Propylene Glycol | 57-55-6 | Ethylene Glycol | 107-21-1 |
| Methylene Dichloride (DCM) | 75-09-2 | Carbon Tetrachloride | 56-23-5 |
How to Use CAS Numbers in Your Procurement Process
- Add CAS numbers to your purchase order template. Make it a mandatory field alongside product name and grade.
- Verify the CoA CAS number matches your PO. When goods arrive, compare the Certificate of Analysis CAS number against what you ordered.
- Cross-check with the SDS. The Safety Data Sheet header must list the same CAS number. A mismatch is a red flag.
- Build a reference list. Maintain an internal list of your regularly procured chemicals with their CAS numbers, approved suppliers, and last-known grade.
Every SPC Product Carries its CAS Number
Every chemical in the SPC catalog is listed with its CAS number. When you request a quote or place an order, cite the CAS number and we ensure the exact specification is supplied — no guesswork, no substitutions.
Browse our full product catalog with CAS numbers →
Specification Snapshot — CAS-Numbered Products Referenced Above
The chemicals used as examples earlier in this guide are all in the SPC catalogue with published CAS numbers. The values below are indicative specification figures for the standard grades supplied — always confirm the exact figure against the batch-specific Certificate of Analysis before you finalise a purchase order.
- Acetone (CAS 67-64-1): purity ≥99.5%, density 0.791 g/cm³ at 20°C, flash point -20°C (closed cup) — indicative.
- Isopropyl Alcohol / IPA (CAS 67-63-0): purity ≥99.8%, density 0.785 g/cm³ at 20°C, flash point 12°C (closed cup) — indicative.
- Methyl Ethyl Ketone / MEK (CAS 78-93-3): purity ≥99.5%, density 0.805 g/cm³ at 20°C, flash point -9°C (closed cup) — indicative.
- Toluene (CAS 108-88-3): purity ≥99.5%, density 0.867 g/cm³ at 20°C, flash point 4°C (closed cup) — indicative.
- Mixed Xylene (CAS 1330-20-7): purity ≥98.5% (xylene isomers plus ethylbenzene), density 0.86–0.88 g/cm³ at 20°C, flash point 25°C (closed cup) — indicative.
- Mono Ethylene Glycol / MEG (CAS 107-21-1): purity ≥99.9% (fibre grade), density 1.113 g/cm³ at 20°C, flash point 111°C (closed cup) — indicative.
- Methylene Di Chloride / MDC (CAS 75-09-2): purity ≥99.9%, density 1.325 g/cm³ at 20°C, boiling point 39.6°C — indicative.
FAQ
Is a CAS number the same as the HSN code used for GST and customs?
No. A CAS Registry Number is a global identifier for one specific chemical substance, assigned once by the Chemical Abstracts Service and never reused. The HSN (Harmonised System of Nomenclature) code is an Indian customs and GST classification used for import duty and tax purposes, and a single HSN code can cover several related chemicals. Quote both on purchase orders and shipping documents — the CAS number pins the exact substance, and the HSN code pins the tariff treatment.
Does SPC provide the CAS number and a CoA with every shipment?
Yes. Every product in the SPC catalogue is listed against its CAS number, and each consignment is despatched with a batch-specific Certificate of Analysis that repeats the CAS number and grade ordered. Packaging follows the product — typically 200–230 litre barrels, IBC totes, or bulk tankers for the solvents and glycols used as examples in this guide — so confirm pack size and CAS number together when you place an order.
How do I get a quote referencing the correct CAS number?
Share the chemical name and CAS number (or grade), the quantity, packaging preference, and delivery location via the contact page. Quotes are typically answered within 4 working hours, Monday to Saturday.