DMSO as Diluent

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

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I know DMSO is not an ideal diluent for HPLC. It will distort the peak shape. Is there any theory or explaination about it? Thank you in advance.

Don't know for sure, but probably just too strong a solvent and causes peak to move with DMSO before actually interacting with column/eluent.

We find DMF is a very good replacement for DMSO. Usually better to make up more concentrated solution and inject 5 ul than to prepare a diluter solution and inject 25 uls.

THF not a bad solvent, but not as good as DMF or DMSO for many of our compounds.

Also use TFA as a solvent. However, can't let compounds with alcohols sit for long time because converts some alcohols to TFA esters in about 1 hour. So prepare and inject fresh. Also, leave the tops off the bottles, because after one injection will dissolve silicones in top and give a lot of mass spec background ions.
Sailor

Are both safe enough for seal and PEEK?

PEEK is incompatible with THF.
-- Tom Jupille
LC Resources / Separation Science Associates
tjupille@lcresources.com
+ 1 (925) 297-5374

Jan,

what type of peak distortion do you get?

Actually I never used more than 10% of DMSO in my sample so I did not have a peak shape issue. What I do is that I dissolve the sample with samll amount of DMSO then dilute it with my mobile phase. I just heard from other people that if you use only DMSO as a diluent and you will see bad peak shape. Anybody has real experience about that?

If the injection volume is small, 5 or 10 uL, DMSO is no problem. It is our preferred saponification solvent, so we have done bazillions of samples with DMSO.

It is a very "strong" solvent and viscous. I expect both these factors are a problem with large volume injections.
Bill Tindall
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