A grade on a chemical label is a promise that the material meets a particular published specification. Different grades are written by different bodies for different purposes, and they are not a single ladder from worst to best: a chemical can be ACS reagent grade and still be unsuitable for chromatography, or HPLC grade and unsuitable for a pharmacopeial use. Knowing who wrote the specification is the key.
The common grades
| Grade | Specification set by | What it guarantees | Typical use |
|---|---|---|---|
| ACS reagent | American Chemical Society, Reagent Chemicals | Purity and impurity limits for general analytical work, with defined test methods | Analytical and general laboratory chemistry |
| Reagent | Supplier, usually to ACS quality where an ACS spec exists | High purity; the supplier’s own certificate defines it | General laboratory use |
| USP | United States Pharmacopeia | Compliance with the USP monograph for that article, including identity, assay, impurities and, for sterile products, sterility and endotoxin | Articles used in or as pharmacopeial products; bacteriostatic water is a USP article |
| NF | National Formulary (published with the USP) | Compliance with the NF monograph, which covers excipients and other non-active ingredients | Benzyl alcohol used as a preservative is Benzyl Alcohol NF |
| FCC | Food Chemicals Codex | Purity for food-ingredient use | Food and flavor applications |
| HPLC | Supplier | Low UV absorbance, filtered, low residue; specified for chromatography | Mobile phases and sample preparation |
| Spectrophotometric / UV | Supplier | Defined transmittance at stated wavelengths | UV-visible work |
| Trace metal | Supplier | Metal impurities at parts-per-billion or lower | ICP and atomic absorption work |
| Anhydrous | Supplier | Water content below a stated limit, often 50 ppm | Moisture-sensitive chemistry |
| Laboratory | Supplier | Reasonable purity with fewer tests than reagent grade | Teaching and preparative work |
| Technical / industrial | Supplier | No guarantee beyond identity and approximate strength | Cleaning and bulk process use |
Where bacteriostatic water fits
Bacteriostatic water is not graded on the ACS scale at all. It is a USP article: the label reads “USP” because the product meets the USP monograph for bacteriostatic water, which specifies the water quality, the preservative labeling, sterility, endotoxin, pH and particulate matter. The benzyl alcohol used to make it meets the Benzyl Alcohol NF monograph. Neither “ACS” nor “HPLC” would be a meaningful grade for it. See what USP means on the label, USP water grades explained and vs. HPLC-grade water.
Reading a grade on a certificate of analysis
A certificate of analysis names the specification the lot was tested against and lists each test with its limit and result. For a graded chemical the specification is the grade; for a USP article it is the monograph edition. If the certificate does not name a specification, the grade on the label is a marketing term rather than a tested claim. See how to read a COA.
Related
What "research use only" means · Glossary
All BAC Water Supply products are supplied for laboratory research use only and are not for human or veterinary use.