I am getting a protonated peak of acetone at m/z 59 when pure solvent is used for electrospray. Since, there is no proton source and only high voltage is applied, the general mechanism of electrospray does not satisfactorily explain the protonation process. The protonation was also observed without electrospray, i.e. when a small microdroplet of the acetone was placed near to MS orifice with a high voltage.
Dear Anil Kumar,
I think your observation is not so unusual. Acetone is hygroscopic solvent and can contain a small amount of water which acts as a source of protons. Moreover, you should take into account that ESI mechanism incorporates not only transfer of ions already existing in solution into gas phase. The interactions in gas phase are also very important. Its easy to imagine such pathway of protonated acetone formation in vapour: CH3COCH3*+ +CH3COCH3 = CH3COCH2* + CH3COCH4+
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