Chromatography Forum

Any Ideas any one
I have an analysis of 50% methanol which contains variable amounts (less than 1000 ppm) formaldehyde and acetaldehyde.

What is best column and conditions.
I would prefer a packed column and as I can do my own packings etc some real odd ball is possible.
Note as a privately owned consulting lab I must watch the dollars and purchasing a new capillary column for a special job which also has a high risk of column damage is not viable.
Job is likely to be only one or two samples a year from an established good client. Cost wise HPLC is not viable and derivitised thin layer would not give the required quantitation.

Bob M

Hi Bob,

Porapak T might do it. 80/100 mesh Isothermal at 140°C. I assume that the balance is water so use an FID. The acetaldehyde will be on the tail of the methanol

The relative retentions on a 1 metre column at 175°C are

Methanol 0.244
Formaldehyde 0.172
Acetaldehyde 0.259

Alternatively use Porapak N
The relative retentions on a 1 metre column at 175°C are

Methanol 1.193
Formaldehyde 0.195
Acetaldehyde 0.222

This one might be a better bet.


Regards,

Ralph

Don't forget you should use fused silica lined SS tubing for the column and a good deactivated glass wool.

All three primary commercial sources of packed columns and their components in the USA carry these.

Also consider since you are packing your own column to pack 2 ft of 'N' with 2 ft of 'Q' when you pack your column. That will maximize your separation of your analytes and keep methanol and water behind the aldehydes.

best wishes,

Rod

Thanks will have a look
I have haysept T on hand as I use in a packed column on my gas analysis GC.
175 C seems to be rather high I thought the max recommended temp on hasept/porapack T was 165 C. I have already tried Carbowax, QF3, OV101 and CS10 at 80 C. QF3 showed the best separation. but I only got one of the aldehydes on my made up test sample.

I will also look over a pile of columns I got from the close down of another lab.

Bob M

Also remember that formaldehyde reacts readily, even with itself to form paraldehyde. Formaldehyde is very difficult to work with and even more difficult to perform accurate chromatography in samples.

Hate to rain on your parade but NMR might be a good choice or react your sample with DNPH and do HPLC to measure formaldehyde.

best wishes,

Rod

Hi Bob,

175°C is OK for Porapak T - it is just below it's limit of 190°C. I can't comment on the Heysep variant. You would probably want to run it at 140°C anyway.

I would be happier trying Porapak N or Rod's suggestion of N and Q in series. From experience, Rod's comment on the difficulty of working with formaldehyde is very valid.

Regards,

Ralph

I never had much joy trying to analyse underivatised HCHO by GC, using either packed or capillary columns.

I used HPLC with 2,4-Dinitrophenylhydazine - the procedure of Lipara and Swarin ( with perchloric acid catalyst ) worked well.

My recollection was that 2,4 dinitrophenylhydrazones were also used by some researchers for GC determination fo formaldehyde and acetaldehyde. If you can't find the publicaations, I'll have the references around here somewhere.

Good luck,

Bruce Hamilton.

We've used HPLC. James R. Dahlgren and Melvin N. Jameson, “Determination of Formaldehyde and Other Aldehydes in Industrial Surfactants by Liquid Chromatographic Separation of Their Respective 2,4-Dinitrophenyl-hydrazone Derivatives,â€

Thanks for the assistance for my aldehyde GC problem.
I chopped an inch off the inlet of second hand 1.5 M Porapac N so that it fitted my machine ran clean up and it worked nicely 150 C isothermal.
On sample however there was a large much wider peak which obscured formaldehyde peak. Chromotropic acid test showed that it could not have been formaldehyde and it looks rather like ethanol both in R value and base width.