ACS Grade chemicals

What ACS grade means

ACS grade identifies a reagent that meets or exceeds the specifications in Reagent Chemicals, the compendium published by the American Chemical Society. Unlike manufacturer-defined grades such as AR, ACS grade refers to a published, publicly available standard: each monograph states the minimum assay, the maximum limits for individual impurities and the test methods to be used. A reagent labelled ACS should therefore mean the same thing regardless of who made it.

The ACS monographs are revised periodically, and a COA for ACS material should indicate that it conforms to the current specification.

Typical specifications

Parameter	Example: hydrochloric acid, ACS
Assay (HCl)	36.5 to 38.0%
Residue after ignition	≤ 5 ppm
Sulfate	≤ 1 ppm
Free chlorine	≤ 1 ppm (by test)
Heavy metals / iron	Low ppm limits as stated in the monograph

Values in the table are typical of the grade. The limits that apply to a given product are those stated on its specification and lot Certificate of Analysis.

Where it is used

• Analytical methods that call for ACS-grade reagents, including many US regulatory and standard methods
• Pharmacopoeial tests where the reagent section refers to ACS specifications
• Quality control laboratories that want a supplier-independent purity standard
• Research requiring consistent, documented reagent purity across suppliers

How it differs from neighbouring grades

AR grade is often equivalent in practice, but its limits are set by the manufacturer. Some AR products exceed ACS limits for particular impurities and some do not test every ACS parameter. Reag. Ph. Eur. and ISO reagent grades are comparable concepts based on European or ISO reagent specifications and may carry dual labelling. LR grade is considerably less pure and is not suitable where ACS is specified. HPLC or spectroscopy grades address instrument-specific properties that ACS monographs do not test. When a method specifies ACS grade, use a product whose COA explicitly states conformity to ACS.

Documentation

For ACS-grade products we supply a lot COA listing each ACS parameter with its result, so you can confirm conformity without further testing.

Ordering ACS grade reagents

Tell us if your method or procedure specifically requires ACS conformity. Where the offered lot is tested to ACS, the COA will say so explicitly. Where only an AR or Reag. Ph. Eur. lot is available, we will say that too, so you can decide whether it is acceptable for your purpose.