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					                                                                                         Atmospheric Pressure Laser Ionization (APLI) Mass Spectrometry
                APLI                                                                     for Measurement of Aromatic Hydrocarbons with Low Polarity
                                                                                         M. Lorenz, L.C. Short, M. Constapel, M. Schellenträger, S. Möschter, O.J. Schmitz, S. Gäb, K.J. Brockmann, S. Droste, and Th. Benter
                                                                                         Department of Chemistry, University of Wuppertal, Gauss Str. 20, 42119 Wuppertal, Germany



             Overview                                                                                                                                                                                                                                     Applications                                                                                                                                                                                                                                                     Conclusions
Analysis of liquid- or gas-phase, non-polar aromatic com-                                                                                                                                                                                                                                                                                                                                                                                                                                                      The 1+1 REMPI (resonance enhanced multi photon ionization)
pounds has been a challenge in several industrial, biomedical
and academic settings. Over the past decade, our group has                                                                                                                                                                                                                                                                                                                                                                                                                                                     at atmospheric pressure provides a powerful tool for the




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developed several laser ionization techniques for gas-phase                                                                                                                                                                                                                                                                                                                                                                                                                                                    determination of compounds containing aromatic systems.
analysis of environmental pollutants, including broad-
bandwidth REMPI and medium pressure laser ionization                                                                                                                                                   Phenanthrene                                                                                                                                                   Fluorene                                                                                                           Fluoranthene
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               These systems exhibit strong absorption bands in the wave-
(MPLI). Using the recently introduced atmospheric pressure
laser ionization technique (APLI), we found a 1000-fold
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               length range 190 nm < λ < 350 nm (S1 ← S0 and S2 ← S0
increase in the detection of non-polar aromatics with mass                                                                                                                                                                                                                                                                                                                                                                                                                                                     transitions).
spectrometry over traditional ionization techniques, such as
                                                                                                                            100   150                                               200            250             300             350                                                                     100     150    200                                        250         300     350                                               100    150     200                    250               300   350
APCI. APLI is a high-efficiency, soft-ionization method and thus
                                                                                                                                                                                          m/z                                                                                                                                                               m/z                                                                                                     m/z
ideally suited to the quantification of non-polar, aromatic
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Applicability of APLI is demonstrated for several aromatics:
hydrocarbons. The source is readily coupled to HPLC and
other pre-separation stages. Potential fields of application
include petro-chemistry, environmental sampling, biomedical
and inorganic research.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        Bio-molecules (e.g., atropine, cotinine, β-estradiol, myosmin)
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Dyes (e.g., Disperse Orange 32, phthalocyanine),
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             Methods
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Heteroaromatics (e.g., benzothiophene, benzothiazole)
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         Ferrocene
                                                                                                                                                                                                       Benzotiazole                                                                                                                                                  Dibenzothiophene
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Organometallics (e.g., ferrocene)
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Halogenated aromatic polymer “building blocks”
A conventional APCI probe is connected to either a HPLC or                                                                                                                                                                                                                                                                                                                                                                                                                                                       (e.g, C50H45Cl, C36H22Br4)
to a direct syringe injection system. The APLI source is a Pyrex
                                                                                                                            100   150                                               200            250             300             350                                                                     100      150   200                                         250        300     350                                               100    150     200                    250               300   350   Pharmaceuticals (e.g, ibuprofen, benzafibrate,)
chamber, based on the Micromass Z-spray(TM) ion source. This
unit couples the HPLC to a Micromass Q-TOF Ultima mass
                                                                                                                                                                                          m/z                                                                                                                                                                m/z                                                                                                    m/z
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Aromatic organometallic coordination complexes
spectrometer.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    (e.g., C76H92Cl Ir N2, C152H184Cl2Ir2N4)
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Heterocyclic organometallic complexes
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 (e.g., C44H47N3P Pd+PF6-, C39H31N2PPdCl2,)
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                                                                                                                                                                                                                                                                                                                                                                                                                                                                   Atropine
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               PAH’s (e.g., mesitylene, fluorene, phenanthrene,
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 anthracene, fluoranthene, benzo[a]pyrene)
                                                                                                                                          Pyrazophos                                                                                                                                                                                                                 Cotinine




                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                Advantages of APLI
                                                                                                                            200   250                                               300            350             400             450                                                                     100      150   200                                         250        300     350                                               100    150     200                    250               300   350
                                                                                                                                                                                          m/z                                                                                                                                                                m/z                                                                                                    m/z
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Only the parent ion M•+ or [M+H]+ is observed. Fragmentation is
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               generally negligible.
An excimer laser provides selective ionization of aromatic
compounds via a REMPI process at atmospheric pressure.                                                                                                                                                                                                                                                                                                                                                                                                                                                         For the detection of PAH the sensitivity of APLI is generally
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               increased by a factor 100 to 3000, as compared to APCI and
Typical solvents show no absorption at 248 nm.
                                                                                                                                                                                                                             Comparison with other techniques                                                                                                                                                                                                                                                  APPI, respectively.
                                                                 Ionization Pathway
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               Dopant assisted APLI is readily available by addition of toluene or
First photon absorption:                                                                                                                                                                                           2 x 228                                                                         EPA PAH12
                                                                                                                                                                                                                                                                                                                                                            2.E+04

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               other potential dopants, ionizing efficiently via (1+1) REMPI. APLI is
                                                                                                                                                                          5561 cts                 2 x 178
                                                                                                                                                                                                                                               APLI                                                                                                                                             252.14
                                                                                                                                                                                                                                                                                                                                                                                                                                                              APLI
                                                                                                                                   normalized signal[arb. units] [a.u.]




                                                                                                                                                                                                             202                                                                                   Naphthalene    128
                                                                                                                                                                                                                                            20 µg/L each

M + hv(248 nm) → M*
                                                                                                                                                                                                                             255            @ m/z 200: 100nM
                                                                                                                                                                                                                                                                                                   Acenaphtylene 152                                                                                                                                          CH3CN/CH3OH200
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               easily adapted to existing AP sources (see photographs).
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                                                                                                                                                                                                                                                                                                   Acenaphtene    154                                                                                                                                         ng/l (1nmol/l)
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                                                                         Ion                                                                                                                     166
                                                                                                                                                                                                                                                                                                   Fluorene       166                                                                                                                                         syringe injection, 200µl/min
                                                                                                                                                                                                                                     278                                                           Phenanthrene   178
                                                                                                                                                                                           154
Secondary reactions:                                                                                                                                                                                                                                                                               Anthracene     178
                                           orbital energy [eV]




                                                                                IP                                                                                        197 cts                                                                                                                  Fluoranthene   202                                       8.E+03

                                                                                                                                                                                                                                               APPI                                                Pyrene         202                                                                                                                                         APCI
                                                                                                                                                                                                                                           2000 µg/L each
M* → A + B             Photodissociation                                                                                                                                                                                                    @ m/z 200: 10µM
                                                                                                                                                                                                                                                                                                   Benzo[a]
                                                                                                                                                                                                                                                                                                   anthracene     228                                                                                                                                         CH3CN/CH3OH10 µg/l
                                                                                S                                                                                                                                                                                                                                                                                                                                                                             (0.5 µmol/l)
M* → M + hv            Light emission                                                                                                                                                                                                                                                              Chysene        228



                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                Acknowledgement
                                                                                                                                                                                                                                                                                                   Benzo[a]pyrene 252                                                                                                                                         syringe injection, 200µl/min

M* + Q → M + Q*        Quenching                                                                                                                                                                                                                                                                   Dibenzo[a,h]
                                                                                                                                                                                                                                                                                                   anthracene     278
                                                                                                                                                                                                                                                                                                                                                                                                253.15

                                                                                X                                                                                                                                                                                                                                                                           0.E+00

                                                                                                                                                                 100                      150                200             250           300                 350                                                                                             150                200          250                                         300          350                            400
Second photon absorption:                                                                                                                                                                                          m/z
                                                                                                                                                                                                                                                                                                                                                               150                 200          250
                                                                                                                                                                                                                                                                                                                                                                                                     m/z
                                                                                                                                                                                                                                                                                                                                                                                                                                            300          350                                 400               The authors thank Prof. Dr. U. Scherf, University of Wuppertal, for
                                                                 internuclear distance                                                                                                                                                                                                                                                                                                                   m/z
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               providing samples. Funding for this work was provided by the MSWF
M*+ hv(248 nm) → M+ + e-     Ionization
                                                                                                                                                                                                  Comparison with APPI                                                                                                                                                                         Comparison with APCI                                                                                            NRW, Germany.

				
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