Ethanol Standards: 190 or 200 proof

[HPLC_Help]

Hi, all -

We are preparing ethanol standards for HPLC analysis to measure fermentation product.

We have been weighing 190 proof ethanol, but haven't been correcting for the fact that it's only 95% ethanol (by volume). We also haven't taken into account that the bottle is a couple years old and has been opened repeatedly (!).

We are considering using 200 proof so we don't have to correct.

Does this sound like a good idea?

Thanks -

H_H

[juddc]

In short, yes it sounds like a most reasonable idea. Better yet, get a CoA and use the purity on that as basis for calculation.

[Consumer Products Guy]

Just make sure what you use is 200 proof ETHANOL, not just 200 proof alcohol. For example, EMD HPLC/Optima Reagent Alcohol is 200 proof, but contains about 5% methanol and 5% isopropyl alcohol.

I think using 190 proof alcohol as the standard is not a good idea, and that, depending on type, can also contain denaturants such as methanol, IPA, or others. We use GC here for our alcohol assays, USP <611>.

[Bruce Hamilton]

I once worked in a manufacturing facility that prohibited non-azeotropic ethanol in the laboratory, so we used a certified AR grade from the 95 - 97% V/V ( at 20/4 ) azeotrope, rather than the more common >99.9% absolute AR grade.

The rule was a consequence of some long-past event where absolute alcohol was purchased, and apparently affected a biological assay. The azeotrope alcohol assay is usually more variable, so certified material is preferable.

In general, using the most purified form is the best option, but it pays to check with colleagues before making changes. I would avoid making standards with alcohol containing any form of denaturant, even if you have to pay tax, as you only require a small quantity for standards.