ESI of protected Arginine peptide

[xinshou]

dear All

I have a peptide of which the only residues are Arginie (7 total ) and Glycine (2 total). The side chains of the Arginine (guanidine) was protected by pbf.

I need to do some modifications to this peptide and plan to use ESI to monitor the reaction progress. As the peptide is not dissolved in water. I am using DMF (dimethylforamide) as solvent.

When I tried to measure ESI, I diluted the peptide/DMF solution 10 times using water, and injected into ESI. However I could not see any expected peaks.

My question is: can I use ESI to detect this peptide ? As the side chains of the Arginine was protected by pbf, is the peptide ionizable under ESI condition? Does DMF do anything bad to the ESI?

[sam.pedraglio]

Are you sure your protecting groups are not "ESI labile"?
Excuse me the stupid question but I'm not familiar with this chemistry.

[xinshou]

Here is the structure of protected Arginine residue:




Please help!

[sam.pedraglio]

In my opinion you shouldn't have any problem detecting your peptide.
Two questions:
1) are you doing an injection or a lc analysis?
2) What do you mean with "Expected peaks"? Are you talking about fragments or charge state?