No peak when injecting a molecul dissolved on DMSO , in RPLC

[dodora]

Hello

i get a strange problem with reverse phase liquid chromatography.

i inject a one hour-reaction-mixture.
eluant: acetonitrile 0,1 % TFA :water 0,1 % TFA with gradient mode. i get nice results (nice peaks).

Then i inject the same reaction-mixture at initial time (t=0 min): i don't get any peak , just a continous line. So i pass ethanol through the column C18 to make it clear. and then i re-inject the same reaction-mixture (t=0); no peak at all.
i pass again ethanol through column. and then i inject a molecule dissolved in eluant. i get one peak which is caracteristic of this molecule.

when i re-inject the reaction-mixture (t=0), i don't get any peak again.

i think that the the reaction-mixture (t=0) cause problems because the molecules are not very soluble in the eluant, may be because the reaction-mixture contains DMSO. So it blocks the column so that i don't get any peak.

but why it shows nice peaks after one hour of heating?? i don't understand.
does DMSO cause any problem in RPLC ??
Please may any one help me to understand.

Best regards.

[tom jupille]

and then i inject a molecule dissolved in eluant

Is this molecule contained in either of your reaction mixtures?

[JGK]

Is the reaction mixture being used to synthesize your molecule? If so, You shouldn't see anything at time zero.

If not:

Do you get a peak if you inject a sample molecule dissolved in eluant with added DMSO (same level as the reaction mix)?

I don't think the DMSO should affect and RP18 column (I've used STDs and samples in 100% DMSO in some analyses).

Column blockage is not an option as your system would show massive pressure fluctuations and probably shutdown.

How is the reaction mixture treated? Does the 1-hour period significantly alter the reaction mixture composition (e.g. removal of volatiles)?

I suspect the problem may be the solubility of the molecule in the reaction mix which is eliminated during the 1 hour reaction period.