dmso/acetic acid

[gcguy]

I am developing a method to seperate dmso and acetic acid. I have moved onto using HPLC for the seperation as the presence DMSO interferes with the acetic acid peak on GC (spliting). I have looked at various C18 and few other columns and have found the best seperation to be on either a Luna or a C8 Zorbax. I am using acetonitrile and water, both with added phosphoric acid. I have tried methanol as well.
I am not getting a suitable seperation, almost but not quite good enough. The sample is about 70% DMSO and about 0.1% acetic acid. I need to determine the acid level.
Any ideas?

GCguy

[Peter Apps]

HI GC guy

What column did you use for the GC ? I get a good separation of dimethyl sulphoxide at about 24 min and acetic acid at about 22 min on a Restek megabore wax column programmed from 30C at 5C/min with hydrogen as carrier at about 12 ml/min. This is from purge and cryotrap samples of African wild dog urine - if you have a nice liquid sample it should be straightforward.

Peter

[gcguy]

Peter,

I agree it is relatively easy to seperate dmso and acetic acid by GC. The problem we were getting was that the acetic acid peak was splitting, this varied as the amount of dmso increased. There are other components in the sample, this may have lead to the issue in the first place.

It would be possible to do the residual acetic using IC but I would rather set up a "standard" hplc method.

GCguy

[Peter Apps]

OK, let's see what the LC experts come up with.

Peter

[Uwe Neue]

Very polar compounds, so I would go with HILIC - silica column, 80% acetonitrile, 20% water, maybe with phosphoric acid if the acetic acid is too retained without it.

[HW Mueller]

gcguy, you do not need to quantify the DMSO? I would think your problem is the ~700x excess of DMSO, so I would use the huge chemical difference between the two, namely that acetic acid is easily dissociated (ionized), so maybe ion exchange should do it.

[gcguy]

For information,

I seem to have got this working now. I am using a C4 column from ACE. ACN/water with phosphoric acid.
Nice seperation in about 5 minutes.

GCguy

[ym3142]

GCguy,

What is your k'?

Thanks for sharing,

[gcguy]

I am getting a k' of about 0.59.

[ym3142]

Thanks, GCGUY