Atmospheric Pressure Laser-Induced Acoustic Desorption Chemical Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for the Analysis of Complex Mixtures

摘要

ABSTRACT: We present a novel nonresonant laser-based matrix-freenatmospheric pressure ionization technique, atmospheric pressure laser-ninduced acoustic desorption chemical ionization (AP/LIAD-CI). Thentechnique decouples analyte desorption fromsubsequent ionizationnby reagent ions generated from a corona discharge initiated innambient air or in the presence of vaporized toluene as a CI dopantnat room temperature. Analyte desorption is initiated by a shocknwave induced in a titanium foil coated with electrosprayed sample,nirradiated from the rear side by high-energy laser pulses. The tech-nnique enables facile and independent optimization of the analytendesorption, ionization, and sampling events, for coupling to anymass analyzer with an AP interface.Moreover, the generated analytenions are efficiently thermalized by collisionswith atmospheric gases, thereby reducing fragmentation.We have coupled AP/LIAD-CI tonultrahigh-resolution FT-ICRMS to generate predominantly [Mþ H]nþ orMþ•nions to resolve and identify thousands of elementalncompositions from organic mixtures as complex as petroleum crude oil distillates. Finally, we have optimized the AP/LIAD CInprocess and investigated ionization mechanisms by systematic variation of placement of the sample, placement of the coronandischarge needle, discharge current, gas flow rate, and inclusion of toluene as a dopant.