Chromatography Forum

Hello every, I bought a vial of reference standard for HPLC but the purity only shows >98.5%. Can I use 98.5% for calculation?

I would use 98.5% but would push the supplier for more information in writing. Of course, my pointy-haired boss would've disagreed, but he typically disagreed with all of my ideas.

I'm assuming here that a different/better source for this reference material is not available. Sometimes, we had to rely on the manufacturer of the active/reference standard, as such reference standard could not be obtained independently.

I would say that a purity of >= 98.5% means that you have a 1.5% potential lack of precision because it could be anything from 98.5 to 100, and that's forced on you by the available standards.

What do you do with it depends on your estimation of the psychology of the supplier, and this is not a thing open to rigorous interpretation. If the supplier was thinking "my customer wants the very highest purity" then if they could have produced 99% pure, they would have done so, and claimed 99% purity; >= 98.5% means = 98.5%.

But if the supplier was thinking "I must not claim higher purity than I can guarantee to deliver in every pot with that label" then the actual purity will be (98.5 + margin-of-safety)%.

Sorry, that doesn't help a lot! I'm inclined to agree with the previous poster, especially the idea of asking the manufacturer exactly what's in the pot!

Is that whats on the bottle or do you have the COA?

Many thanks to all of your replies. > 98.5% is the value observed in both of label and CoA. The reference standard I am using is from Sigma. Guessing that using the value of > 98.5% is not acceptable since the actual value is not determined, maybe I have to change another supplier.

Depends upon final use.

EPA uses the following language:
When a compound purity is assayed to be 96% or greater, the weight can be used without correction to calculate the concentration of the stock standard.

For the purpose of environmental regulation >98.5% is as good as 99+%