Interfering peak in DMSO

[hotliner61]

In my lab we routinely test for residual solvents using a DB-624 30m x 0.53mm x 3 um column. When DMSO is used as solvent we always find a small unknown peak in the blank which interferes with early eluting peaks (usually methanol .
No matter how we change the chromatographic conditions, that interfering peak is always there.
We tried different vendors but to no avail. Any suggestion on how to circummvent the problem?

[chromatographer1]

In my experience the peak may be methylamine.

You could try putting a small piece (3 meters) of SPB-1000 in front of the 624 column.

This will make a slight change in the selectivity of the column but try it and see. I did something similar in my paper published in AC in June 1997

best wishes,

Rod

[Terry]

hotliner61:

I also have tested DMSO from a variety of manufactuers, and find that of Burdick & Jackson (Honeywell) have the minimum interfering peak for methanol. You may try this brand.

Rod:

I think the artefact which shows interference with methnol may be methylsulphide or dimethylsulphide.

DMF or DMAc usually give rise to artefacts like methylamine and dimethylamine.

Regards

Terry

[chromatographer1]

Oops !

Late night mental slip. Neurons got crossed. Of course, you are correct and I should have been in bed by the time of my response.

Thanks for the correction. I knew better

best wishes,

Rod

[Terry]

This happens sometimes

Surely you have done well, and I have read the paper you mentioned, it is great.

Bed time for me, bye for now

Best wishes

Terry

[hotliner61]

Thank you Rod, I'll try your suggestion. Also, do you have a reference for the paper you mentioned?

[chromatographer1]

Since DMDS and DMS as well as Methyl Mercaptain are the likely impurities, a column with basic characteristics should be picked to remove or reduce these sulfur based methanol peak interferences.

A Carbowax suitable for amine analysis would be the best choice.

If you were trying to remove methylamine (as I confused DMSO with DMF previously) then an acidic phase such as SPB-1000 would be a good choice.

Here is the reference. Search for "headspace" and "Rodney George" using Google Scholar and you will find it.

Anal. Chem., 69 (11), 2221 -2223, 1997. 10.1021/ac970040u S0003-2700(97)00040-1

Copyright © 1997 American Chemical Society

Analysis of USP Organic Volatile Impurities and Thirteen Other Common Residual Solvents by Static Headspace Analysis

Rodney B. George* and Preston D. Wright
Analytical Research, R&D Services, Mallinckrodt Inc., P.O. Box 5439, Saint Louis, Missouri 63147-0339

Received for review January 14, 1997. Accepted March 26, 1997.

Abstract:

Static headspace gas chromatography was investigated for the analysis of residual solvents in size-limited samples. The advantages of improved limits of detection at low ppm levels and decreased sample size requirements were realized. This methodology allows the measurement of 18 common residual solvents in 6 min using 1 mg or less of sample. Greater recovery of analytes from pure dissolution solvents without the use of salts became possible when smaller preparations of samples were combined with the use of smaller vials. Rapid equilibration of the static headspace sample preparations was an additional benefit of this modification. Optimized chromatography was developed to take advantage of the shorter equilibration time and to increase instrument productivity.

best wishes,

Rod