I synthesized 4 peptides, one with no aminooxy group and others 3 with a N-terminal aminooxy group. How ever in all later 3 cases including my expected peak for peptide in LC-MS I also observe a major side product corresponding a increased mass of 40 Da. I suspect the presence of aminoxy group is doing some side reaction!
Dear Shubhendu Palei ,
It might be potassium (K, 39.098). I have observed the same phenomenon with some of my compounds.
Rafik
Dear Shubhendu Palei ,
It might be potassium (K, 39.098). I have observed the same phenomenon with some of my compounds.
Rafik
Dear Rafik,
That is very much possible. But a completely different peak in HPLC should not correspond to K+adduct of the parent ion?
Dear Shubhendu,
Generally when I did LC-MS for some of my compounds I observed two peaks one for the parent ion and the other for the potassium adduct. In other case, only the K adduct was observed.
Rafik
Dear Rafik,
I understand your point. My point is a K adduct should not have a different retention time in HPLC in addition to the parent ion peak. I see a completely different peak besides the parent ion!
The acetone oxime derivative would also give you +40 Da. Is it possible that your aminooxy peptides have been exposed to acetone (eg from glassware or dry ice bath)?
You can perform high resolution MS and the accurate mass of the adduct observed will give you the answer.