Analysis of alcohols...

[mordacious]

Hello

I plan on using sorbent tubes and impingers to collect alcohol emissions very soon. I know I can analyze alcohols using GC but my GC is in use most of the day while I use the HPLC maybe 3 hours a day.

I've been looking for derivatization reagents for alcohols and I found phenyl isocyante. I'm pretty new to HPLC but I have a feeling this won't work as I'm collecting the alcohols in water.

Does anyone have any ideas? Time is an issue as I am the only one who runs GC and HPLC in our lab and I'll have around 36 samples to prepare each week.

Thank you,
Ashley

[Serg]

Hi mordacious,

I believe that isocyanates can be used with dry samples only; I thought about lyophilization, but I am afraid that alcohols will go away during the drying process. The other thing to try would be some kind of acyl chloride, like benzoyl chloride in alkaline conditions. This should work.

Good luck.
Serg.

[mordacious]

Hi mordacious,

I believe that isocyanates can be used with dry samples only; I thought about lyophilization, but I am afraid that alcohols will go away during the drying process. The other thing to try would be some kind of acyl chloride, like benzoyl chloride in alkaline conditions. This should work.

Good luck.
Serg.

Thanks, I found a procedure using benzyl chloride and NaOH in pet ether but the water is still an issue Extraction time perhaps...

Ashley

[Mark Tracy]

If you use sorbent tubes, you can derivatize in situ, then recover the derivative. Just use enough excess reagent to react with stray moisture.

[Serg]

Well, I am quite sure, that BENZOYL chloride (chloranhydride of benzoic acid) can be used to modify alcohols in aqueous solution at alkaline pH. It takes time to hydrolyze it and it is sufficient to derivatize alcohols. Check for "ethylen glycol" in serum, for example.

Good luck.

[Consumer Products Guy]

Ash - Tell your pointy-haired boss that you need the right tools to do the job right, in this case: an additional GC. He/she would probably expect one to cook without heat. You may want to explore ways to speed up your existing chromatography on your GC to "open up" some time on it. However, polar GC columns are generally used for alcohols, and your existing GC procedures may take the oven up too high for those, so you'd have to routinely swap out the polar column in that case. I sometimes ask for guidance from management in how to cook a three minute egg in two minutes....not everyting is possible using only stuff at hand...

[HW Mueller]

Serg, if you are sure you should be able to tell us how you envisage your derivatization.

[Serg]

Well, correct me if I am wrong: briefly, add C6H5COCl to your chilled alcohol containing sample (NaOH is already there), vortex, incubate for ~5-10 min, then hydrolyze excess of benzoyl-Cl, extract with RP-SPE, analyse. Something like this. At least it works for glycols...

Regards.
Serg.

[HW Mueller]

So nothing aqueous now?

[juddc]

HI Ashley -

It can be done by LC but without derivitization, sensitivity may be a real issue for you.

Check this:

http://www.shodex.com/english/dc0805.html

I've used these columns for analysis of ferments with some good success.

I believe the benzoyl chloride derivitization will work in the presence of water - I tried it with some slightly higher MW glycols and it worked, but I found it to be a PITA and not particularly well suited for the samples I was looking at.

CJ

[mordacious]

Thanks for all the input guys!

Ashley

[Hollow]

Maybe the derivatization with DABSYL-Cl is another possibility.

I once just run into the dead end, as I was trying to derivatize an amine dissolved in MeOH.

After some work, I realized that the peak I was pressuming to be my analyte was MeOH-DABSYL...

[HW Mueller]

juddc,
you had an alkaline pH and got derivatization? % yield? 10^6 excess of benzyl chloride?

Hollow,
that´s what water in the system does.

[juddc]

Yes, I did get derivitization of glycols in the presence of water at alkaline pH with a large excess of benzoyl chloride.

I showed that the procedure was linear and had the sensitivity I needed, but I abandoned it due to matrix issues in the samples I was working with, so I never got to figuring absolute yield. I found that there were too many other things in the samples for benzoyl chloride to react with, making the prospects for good recovery and development of a broadly applicable chromatography method too slim to be pursued in the time that I had available.

If you're interested, the paper below is where I started:

J Chromatogr B Biomed Appl. 1996 Oct 25;685(2):370-4.
Serum ethylene glycol by high-performance liquid chromatography. Vollmer PA, Harty DC, Erickson NB, Balhon AC, Dean RA.

[HW Mueller]

OK, so you probably reduced the water and OH- (by forming benzoic acid and HCl, the latter taking care of OH-) to a point where it gave the reaction with the glycols a chance.