[curiouscat]

Is there a quantitative analytical method that would let me estimate the total -OH content in my liq. sample?

Or is "total -OH"  too broad a specification to have a generic estimation?

I googled a bit but did not find anything useful; any pointers are welcome!

[marquis]

If your sample is just plain water and alcohol mix, then a quick and dirty method is to measure the refractive index (RI).  The handheld refractometers are cheap and often used in wine and grape testing. 

Make up known alcohol solutions and measure the RI.  The do a concentration vs % alcohol curve as a standard.  And measure your unknown.

This is a very quick and dirty method.  Depending on your unknowns and degree of accuracy, it may not be suitable.

Good luck.

[curiouscat]

Sorry, I should have explained better. The alcohols in the mix are unknown; not looking at just ethanol.

To explain my application further; we are synthesizing a higher alcohol  and obtaining only ~85% selectivity. Based on the reaction mechanism, we suspect related alcohols might also be getting formed and we want to verify if this is so and how much.

That's where we were thinking a total alcohol content test might have helped.

[Arkcon]

Its hard for me to think of a colorimetric reaction, specific to just alcohols, and to all alcohols at the same rate, regardless of the carbon chain, for you to build a standard and check with a spectrometer.  But maybe one of our real organic chemistry experts knows one.

Seems like you could get a result by IR spectroscopy, but I don't know anything about quantitative IR.

If you have enough sample, maybe you could fractionally distill?  You would also get a ballpark number to the general composition, if not the absolute composition.  I.E. -- small alcohols have lower b.p than longer ones, the very longest ones may char if you don't vacuum distill, but at least you get those three groups as volumes, and maybe a few more in between.

[vex]

Seems like you could get a result by IR spectroscopy, but I don't know anything about quantitative IR.

Quantitative IR is tough; figuring it out might be more trouble than it's worth.

Do you have access to GCMS or HPLC? I know that in the CO2 reduction literature, a number of products are often formed, some of which are alcohols. They usually sample the entire reaction and headspace by GCMS, but if you're only interested in liquid products, you can probably use HPLC.

[Stepan]

Quantitative IR is OK as long as you can live with +/-15% error. Good news: you can use Quartz cuvette instead of salt.

[curiouscat]

Quantitative IR is tough; figuring it out might be more trouble than it's worth.
Do you have access to GCMS or HPLC?

Thanks for the sugesstion! Yes I have access to both.

Quantitative IR is OK as long as you can live with +/-15% error.

That'd be too large an error for my application I think. In any case, can quantitative IR be done on an unknown alcohol? Do all alcohols have absorption at a specific λ and is the intensity in mixtures additive?

[curiouscat]

But maybe one of our real organic chemistry experts knows one.

That's what I'm hoping for! 

If you have enough sample, maybe you could fractionally distill?  You would also get a ballpark number to the general composition, if not the absolute composition.  I.E. -- small alcohols have lower b.p than longer ones, the very longest ones may char if you don't vacuum distill, but at least you get those three groups as volumes, and maybe a few more in between.

Sample quantity is not a problem; I've literally liters of it. That's a good idea. I'll try and distill it. We had tried initially, but they seemed pretty close boiling so we had trouble separating.

[Stepan]

If you think about distillation, why don't you do GC MS first to see what is there. After that you can build a standard and do your samples with high accuracy by GC FID. If you need testing, I can assist.

[curiouscat]

If you think about distillation, why don't you do GC MS first to see what is there.

Thanks! I am in the process of doing a GC-MS now. Let's see if I can identify what I have in there.