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Atmospheric‐pressure laser ionization: a novel ionization method for liquid chromatography/mass spectrometry
Author(s) -
Constapel M.,
Schellenträger M.,
Schmitz O. J.,
Gäb S.,
Brockmann K. J.,
Giese R.,
Benter Th.
Publication year - 2005
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.1789
Subject(s) - chemistry , atmospheric pressure laser ionization , photoionization , atmospheric pressure chemical ionization , ionization , mass spectrometry , direct electron ionization liquid chromatography–mass spectrometry interface , chemical ionization , ion source , electron ionization , ambient ionization , analytical chemistry (journal) , desorption electrospray ionization , electrospray ionization , chromatography , ion , organic chemistry
Abstract We report on the development of a new laser‐ionization (LI) source operating at atmospheric pressure (AP) for liquid chromatography/mass spectrometry (LC/MS) applications. APLI is introduced as a powerful addition to existing AP ionization techniques, in particular atmospheric‐pressure chemical ionization (APCI), electrospray ionization (ESI), and atmospheric pressure photoionization (APPI). Replacing the one‐step VUV approach in APPI with step‐wise two‐photon ionization strongly enhances the selectivity of the ionization process. Furthermore, the photon flux during an ionization event is drastically increased over that of APPI, leading to very low detection limits. In addition, the APLI mechanism generally operates primarily directly on the analyte. This allows for very efficient ionization even of non‐polar compounds such as polycyclic aromatic hydrocarbons (PAHs). The APLI source was characterized with a MicroMass Q‐Tof Ultima II analyzer. Both the effluent of an HPLC column containing a number of PAHs (benzo[ a ]pyrene, fluoranthene, anthracene, fluorene) and samples from direct syringe injection were analyzed with respect to selectivity and sensitivity of the overall system. The liquid phase was vaporized by a conventional APCI inlet (AP probe) with the corona needle removed. Ionization was performed through selective resonance‐enhanced multi‐photon ionization schemes using a high‐repetition‐rate fixed‐frequency excimer laser operating at 248 nm. Detection limits well within the low‐fmol regime are readily obtained for various aromatic hydrocarbons that exhibit long‐lived electronic states at the energy level of the first photon. Only molecular ions are generated at the low laser fluxes employed (∼1 MW/cm 2 ). The design and performance of the laser‐ionization source are presented along with results of the analysis of aromatic hydrocarbons. Copyright © 2005 John Wiley & Sons, Ltd.