When purchasing chemicals from Sigma, Fisher, or wherever, there are often -grade's attached to their description like reagent-grade, technical-grade, analytical-grade, or more niche-sounding biotech-grade, HPLC-grade, DNA grade (DNase free perhaps?)

Is there some sort of standard for what these actually mean or are they arbitrary, differing from supplier to supplier or even chemical to chemical? Beyond the 'niche' grades, is there a common order of purity between the others or do they depend on the types of impurities?

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    Grades don't mean much. Learn how to purify lesser quality chems yourself. Or pay the HUGE markups of the big-box chem suppliers. Example: Sigma Aldrich HPLC Acetone 99.9%. 1 liter costs $94 plus shipping plus hazmat etc. Instead, we buy somewhat recycled/cleaned acetone from local industry. Several liters can be processed daily by one person with a 3-5L flask, a stillhead, and the other general kit involved. Our cost per liter including KMnO4 and a little silica xerogel is under one US dollar. After a day or two in a sealed bottle over a little dessicant and POW. HPLC suitable acetone, clean – Mario Lopez May 21 at 23:35

Sigma-Aldrich gives a very useful table outlining what the different purity levels are and suggested applications. I was less successful at finding equal documentation from some of the other suppliers, but the analysis for the purity of the chemicals they sell is in the catalog and on the bottle.

In general, technical grade or laboratory grade are the lowest purity. ACS Reagent grade means that the chemical conforms to specifications defined by the Committee on Analytical Reagents of the American Chemical Society (but Aldrich "ReagentPlus" means >95% pure). So, "ACS Reagent grade" chemicals should be comparable from different suppliers. Analytical grade is generally the most pure.

For some of the other grades, such as HPLC grade solvents, the issue is less about overall purity than about being free of substances that would interfere with a particular application. I've reproduced a piece of the table below to give you an idea of the information available.

enter image description here

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    "Reagent grade" is not mentioned in the table. So what's "reagent grade" compared to "ACS reagent"? – Sparkler May 30 '16 at 14:38
  • I guess the follow up question would be "what/where are the ACS specs"? – Nick T Nov 23 '16 at 17:34
  • @NickT The ACS specs depend on the particular chemical under discussion. Janice did provide a link for more info: pubs.acs.org/reagents/index.html – R.M. Nov 23 '16 at 21:08

At the company Puritan Products, the reagent grade designation is used to describe high purity chemicals for which no established specifications exist. Apparently, this is often the case with products diluted from ACS grade products, as some of these cannot be ACS reagent grade in dilution by the standards that ACS sets.

Source

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