Instrumentation and Characterization of Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

By combining the advantages of desorption electrospray ionization (DESI) and atmospheric pressure chemical ionization (APCI), a novel ambient surface desorption atmospheric pressure chemical ionization (SDAPCI) source is developed for direct detection of trace amounts of analytes in various complex matrices without any sample pre-treatment. In the SDAPCI source, a self-assembled corona discharge was employed to generate the primary ions, which were directed to impact the sample surface to yield positive/negative ions of analytes for mass analysis. Using ambient air (about 45%–60% relative water moisture) as a reactive reagent for chemical ionization to generate primary ions such as H3O+ in positive ion detection mode or H2O·OH− in negative ion detection mode, SDAPCI allows mass spectrometric analysis of ambient samples without toxic contamination, and provides simplicity in its implementation for in-situ analysis in a miniature mass spectrometer. The principle and construction of an SDAPCI source are presented in this contribution. Successful detection of trace amounts of active ingredients of various pharmaceutical preparations was demonstrated using the homemade SDAPCI source with ambient air as the reactive reagent. Using pure argon gas instead of the ambient air, radical cations of acetaminophenol and peptide I–7 were successfully observed and structurally characterized by MS/MS experiments, which provided the experimental evidences for the production of radical cations of peptides at atmospheric pressure. The data show promising applications of SDAPCI-MS for direct analysis of ambient surfaces with neither sample pre-treatment nor toxic chemical contamination.