Hi all
I would like to know if it is possible to read the ethanol concentration in a liquid by spectrometry (but the liquid could contain other colors), and if yes, how to (on which frequencies do the ethanol absorbs light ?)
Thank you

There are many ways to measure this. What is the ethanol dissolved in?

In fact I want to measure the ethanol concentration in an spirit glass.

Is there a translation problem here?

spirit glass

http://www.johnlewis.com/home-garden/glassware/spirit-liqueur-glasses/c800008047

Spirit level

http://en.wikipedia.org/wiki/Spirit_level

 

Anyway, Ethanol doesn't absorb visible light.

You could measure it by infra red absorption spectroscopy (or, in principle, by short wave UV but that's not going to be easy).

You could also measure it by NMR

 

By far the easiest way to get a reasonable estimate of an alcohol concentration is to measure the density.

 

What equipment do you have access to?

I'm going to second John's answer. I think short wave UV (or arguably NMR depending on the instrument's field strength) would be the most accurate method. However, the UV route may be problematic depending on what other species are in your sample.

 

I do not recommend IR spectroscopy for a number of reasons. I'll be glad to tell you why if you are curious.

 

A density measurement would give you a quick check with reasonable accuracy.

 

This all depends on your access to equipment and precision requirements though.

If nearly all the rest is water, then a refractometer is the standard method.

http://en.wikipedia.org/wiki/Refractometer

 

Or a hydrometer

http://en.wikipedia.org/wiki/Hydrometer