Multiphoton ionization, mass spectrometry

AFID = alkali-flame ionization detection FID = flame ionization detection FPD = flame photometric detection GC = gas chromatography IGEFET = interdigitated gate electrode field-effect transistor ITMS = ion trap mass spectrometry MIMS = multiphoton ionization mass spectrometry MS = mass spectrometry... 

Gas chromatography with a flame photometric detector (Sass and Parker 1980) and multiphoton ionization mass spectrometry (MI/MS) (Syage et al. 1988) have also been used to analyze diisopropyl methylphosphonate in air samples. 

A number of other laser spectroscopic techniques are of interest but space does not permit their discussion. A few specialized methods of detecting laser absorption worthy of mention include multiphoton ionization/mass spectrometry (28), which is extremely sensitive as well as mass selective for gas-phase systems optically detected magnetic resonance (29) laser intracavity absorption, which can be extremely sensitive and is applicable to gases or solutions (30) thermal blooming, which is also applicable to very weak absorbances in gases or liquids (31) and... 

By employing a laser for the photoionization (not to be confused with laser desorption/ ionization, where a laser is irradiating a surface, see Section 2.1.21) both sensitivity and selectivity are considerably enhanced. In 1970 the first mass spectrometric analysis of laser photoionized molecular species, namely H2, was performed [54]. Two years later selective two-step photoionization was used to ionize mbidium [55]. Multiphoton ionization mass spectrometry (MPI-MS) was demonstrated in the late 1970s [56—58]. The combination of tunable lasers and MS into a multidimensional analysis tool proved to be a very useful way to investigate excitation and dissociation processes, as well as to obtain mass spectrometric data [59-62]. Because of the pulsed nature of most MPI sources TOF analyzers are preferred, but in combination with continuous wave lasers quadrupole analyzers have been utilized [63]. MPI is performed on species already in the gas phase. The analyte delivery system depends on the application and can be, for example, a GC interface, thermal evaporation from a surface, secondary neutrals from a particle impact event (see Section 2.1.18), or molecular beams that are introduced through a spray interface. There is a multitude of different source geometries. 

Sub-Doppler Measurement of Excited-State Rotational Constants and Rotational Coherence by Picosecond Multiphoton Ionization Mass Spectrometry, N. F. Scherer, L. R. Khundkar, T. S. Rose, and A. H. Zewail, J. Phys. Chem. 91, 6478 (1987). 

Lindner J, Grotemeyer J, Schlag EW (1990). Applications of multiphoton ionization mass spectrometry Small protected nucleosides and nucleotides. Int J Mass Spectrom Ion Proc 100 267-285. 

The cresols and other lower alkylphenols have been studied by multiphoton ionization mass spectrometry (MPI) with the aim of distinguishing positional isomers. Only slight differences were found in some cases, mainly concerning the low-mass region. Remarkably, the MPI mass spectrum of ortho-cresol was again distinct becanse water loss, i.e. a primary fragmentation reaction, from ions o-7 + was fonnd to be significantly more frequent than with the other isomers . ... 

Grotemeyer, J., Boesl, U., Walter, K., and Schlag, E.W, "Biomolecules in the Gas-Phase 2 Multiphoton Ionization Mass-Spectrometry of Angiotensin-i," Or. Mass Spectrosc. 21, 595-597, 1986. 

J. Grotaneya and E. W. Schlag, Multiphoton ionization mass spectrometry, Angew. Chem. 27, 461-474 (1988). 

Lubman, D.M. (1988) Analytical multiphoton ionization mass spectrometry. Part I. Theory and instrumentation. Mass Spectrometry Reviews, 7, 535-554. 

Zimmermann R, Lenoir D, Kettrup A, Nagel H and Boesl U (1996) On-line emission control of combustion processes by laser-induced resonance-enhanced multiphoton ionization mass spectrometry. Twenty Sixth Symposium (International) on Combustion, pp 2859-2868 Pittsburgh The Combustion Institute. 

Apart from the galvanic detection of the ion currents, direct mass spectrometric detection of the ions can also be applied, as is the case with resonance ionization mass spectrometry (RIMS) [676]. In addition, ionization can be performed by multiphoton absorption, which requires very intense primary sources. 

This article discusses why one would choose nonresonant multiphoton ionization for mass spectrometry of solid surfaces. Examples are given for depth profiling by this method along with thermal desorption studies. 

Surface Analysis by Laser Ionization Post-Ionization Secondary Ion Mass Spectrometry Multi-Photon Nonresonant Post Ionization Multiphoton Resonant Post Ionization Resonant Post Ionization Multi-Photon Ionization Single-Photon Ionization... 

The general principle of detection of free radicals is based on the spectroscopy (absorption and emission) and mass spectrometry (ionization) or combination of both. An early review has summarized various techniques to detect small free radicals, particularly diatomic and triatomic species.68 Essentially, the spectroscopy of free radicals provides basic knowledge for the detection of radicals, and the spectroscopy of numerous free radicals has been well characterized (see recent reviews2-4). Two experimental techniques are most popular for spectroscopy studies and thus for detection of radicals laser-induced fluorescence (LIF) and resonance-enhanced multiphoton ionization (REMPI). In the photochemistry studies of free radicals, the intense, tunable and narrow-bandwidth lasers are essential for both the detection (via spectroscopy and photoionization) and the photodissociation of free radicals. 

Photolysis of the dimer, reaction (44), proceeds primarily via generation of Cl + ClOO (Cox and Hayrnan, 1988 Molina et al., 1990). For example, Molina et al. (1990) reported the quantum yield for this channel at 308 nm to be unity, with an uncertainty of 30%. Okumura and co-workers (Moore et al., 1999) and Schindler and co-workers (Schmidt et al., 1998) have reported that the quantum yield is less than 1.0. For example, Schmidt et al. (1998) used resonance-enhanced multiphoton ionization (REMPI) with time-of-flight (TOF) mass spectrometry to follow the production of oxygen and chlorine atoms as well as CIO in vibrational levels up to v" = 5 in the photolysis of the dimer. At a photolysis wavelength of 250 nm, the quantum yield for chlorine atom production was measured to be 0.65 + 0.15, but CIO was not observed. Assuming that all of the excited dimer dissociates, this suggests that the production of CIO in vibrational... 

Zimmerman, R., Heger, H.J., Kettrup, H.J., Boesl, U. (1997) A mobile resonance-enhanced multiphoton ionization time-of-flight mass spectrometry device for online analysis of aromatic pollutants in waste incinerator flue gases first results. Rapid Commun. Mass Spectrom. 11 1095-1102. 

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