Chromatography Forum

HI!! I have a problem with ALCOHOL DETERMINATION (from USP)

I determined the density (at 15.56) of my solution. The result is 0.8115.

How I can find the % ww and %VV??

In the table there are 8 columns!!




I don't understand

I had problems..too!

It remains a mystery to me!

Ahhh - your first post.

I will answer that I have been able to understand little of USP in 4+ decades, everything seems unclear there to me. We assayed ethanol in products by gas chromatography, validated our own method. Yes, ethanol is typically reported in volume/volume % historically.

Concerning ethanol USP monograph, there has been no assay procedure included. After contacting them, USP told me it was specific gravity as assay procedure even though not stated in the Monograph, seemed aggravated that I "just didn't know that".

If I'm reading the chart right, I think your concentration, by volume, is 96%.

I've been very confused by why alcohol content is done by specific gravity instead of something more analytic. If you want something more accurate, IMHO, I'd look into a GC method.

I've been very confused by why alcohol content is done by specific gravity instead of something more analytic. If you want something more accurate, IMHO, I'd look into a GC method.

It's because the USP is so outdated and out of touch with reality.... Their chart "assumes" that the "sample" contains alcohol and water ONLY.


I like that the Monograph for 99.5% glycerin states it can contain up to 5% water !!!

The comment I received when asked about why we are using charts made by some guy, circa 1890, for alcohol concentration was usually a swear directed at Carrie Nation.

I wrote to the USP. They say that in fact it is an anachronistic mechanism. Unfortunately the USP asked to determine the title of ethanol with tables! I challenge anyone to measure the density at 15,56 ° C !!!

I'm guessing this is all down to whisky distillers needing a quick way to know where they've got to, and customs/tax people insisting on whisky distillers being able to measure what they've made (and pay tax) before it gets let out of the box. I vaguely remember visiting a historic distillery in Scotland where the final stage was a measuring set-up in a mahogany/glass cabinet with a hydrometer that could be moved by knobs and dials from outside the cabinet. The entire cabinet was locked with a padlock whose key belonged to the Customs people and this device was supposed to secure the measurement of Whisky in some exciting way so that the operators couldn't syphon it off without the tax people knowing. I can't remember quite how it all worked...