Aldehydes in glycerol..

[Pegry]

Hi everybody,

we have to measure the concentration of the aldehydes in some samples of glycerol. We are interested in formaldehyde, acetaldehyde, propanaldehyde and also in some hydroxy-aldehydes like glyceraldehyde and glycoladehyde.
We have tried to derivatize the aldehydes with PFBHA (pentafluorobenzyl hydroxyl amine) and measure them with GCMS. We had success in measuring formaldehyde, acetaldehyde and propanaldehyde but we got no signal with the hydroxyaldehydes.
Could this be caused by the interactions of the OH group with the injector-column?
Do you have some experience in measuring hydroxyaldehydes maybe with HPLC? Which derivatization agent, in your experience, would be better to use for this application (DNPH, others)?

Thanks in advance for any information,

Have a good day..

[Uwe Neue]

DNPH will work. A few years ago, we did a fair amount of work with air samples, but the story should be similar with liquids. Analysis by HPLC. You can look at the Waters website for details.

[Consumer Products Guy]

Pegry - can I ask why you need to measure these? My company makes USP glycerin and doesn't look for these species, just wondering

[Bryan Evans]

Below is an application of DNPH aldehydes separated on Cadenza CD-C18:

http://www.silvertonesciences.com/files/TI020E.pdf

[Bryan Evans]

Because glycerol is quite viscous - you may have to dilute it down with
water before injecting it into a C18 phase (dont' know for sure, just a thought).

[mbicking]

Years ago I developed an LC method for aldehydes. It eventually became EPA Method 8315 ( and 8316). The current version should have some details about conditions. It is similar to the air sampling methods, but not exactly the same.

We looked at a number of reagents and found that DNPH was the easiest to use. We also considered GC reagents, but they offered no real advantage for liquid samples.

In general, the larger aldehydes react more slowly, and may require more time, or temperature, or both. If you have a separation problem, try a different C18 column, with differing selectivity.

Write back and let us know how things work out.

[Pegry]

Thanks for the answers..

We have tried the analysis by GCMS and HPLC... With HS-GCMS we get a good sensitivity for formaldehyde and acetaldehyde but no signal for the hydroxy-aldehydes..Probably we would need to silylate the OH group in order to see them in GC..
We had better results with HPLC-UV and derivatization by DNPH. We have developed a method based on EPA 3015 and it works good for our job...

Best regards

[mbicking]

Sorry I didn't address the hydroxy-aldehydes. You are correct that they are not likely to be volatile enough for GC, especially once you add on the reagent, and there may be side reactions happening as well. I doubt that you want to do a second derivatization, which would be nearly impossible in a glycerol matrix (more hydroxyls!).

Depending on your equipment and reaction conditions, it may be possible to do the derivatization on-line, in the autosampler. I have never done it for this reaction, but it is certainly possible, and works with other derivatization reagents.

Good luck.