I am trying reactions of peptide with organic molecule in phosphate buffer (pH 7.0) .But while monitoring the reaction by LCMS due to higher salt concentration ,I am not getting the Mass spectrum. The solubility of peptides in water is high.Reaction concentration was 0.5mM.To dissolve the organic molecule 30% DMSO is also used
Since you are using LC-MS, there are several things that could be happening.
What sample preparation do you do? I also think that it's not the salt that is screwing things up (if you are concerned, you can disconnect the MS until the injection peak is off).
What kind of peptides do you use? Lots of positive charges? In that case, they will indeed elute in the injection peak.
How much do you inject? straight from this mixture? The 30% dmso may cause your peptide to "flush through" the column. I suggest dluting it.
To add to Dr. Verhelst's reply, if the peptide can take multiple charges, it may be showing up at an m/z of the molecular weight divided by the number of charges. This usually leads to a unique pattern of peaks in the mass spectrum.
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