Does anyone know (or use) whether there is any way of cleaning up a sample which is only 20-40ul in volume before injection onto a column? There are some particularly hydrophobic compounds within our samples which run very late on the column with respect to the eluants we are interested in. It would be nice to leave them behind on a prep. phase and then inject the sample without them. I know we can just change the constitution of our mobile phase but wondered whether sample prep might be an alternative.

how about diluting with water, spe, evaporate, redisolve in 20-40 µl of solvent?

Dear anonymous, thanks for replying and sorry for my ignorance but what is "spe"?

Dear Nick A!
SPE it's an abbreviation for solid phase extraction, one of the potential solutions in your case. Using of the RP precolumn in order to trap hydrophobic compounds also can be considered as well as microexration ( modern autosamples contains an option for needle heigh tunning and as a result gives a possibility to inject from two phase solutions ( from lower of upper layer).
I'm sure that at least few other options can be evaluated.

Dr.A.Weisman
Chemagis Ltd.,
Israel

I once used a pipette tip hand packed with C-18 from an old column to remove displacer from some fractions collected during displacement experiments.

I have seen similar pipette tips now comercially available. I think these may work for your application. Good Luck

You can do this off-line with an SPE cartridge or online with an SPE column and a switching valve. Inject the complete stuff on the precolumn, elute the part of the sample that you want to analyze, then take the precolumn off-line for a brief wash with high organic.