Surface ionization mass spectrometry

The terms surface ionization mass spectrometry (SIMS) and ion sputtering are often used when accelerated atoms such as Xe or ions such as Ar+ strike a surface causing ionization of the material on the surface. The surface can be solid or liquid in the form of a solution or a suspension in the solvent. In this section, the terms fast atom bombardment (FAB) and fast ion bombardment (FIB) will be used. 

Stoffels, J. J A Direct Inlet for Surface-Ionization Mass Spectrometry of Airborne Particles, Inf. J. Mass Spectrom. Ion Phys., 40, 223-234 (1981b). 

White, F.A., 1%8, Surface Ionization , Mass Spectrometry in Science and Technology, (Wiley, NY, London, Sydney) 62. 

Surface-ionization mass spectrometry (SI-MS) studies of organic compounds show that in most cases the compounds decompose into radicals, which have a lower ionization energy IE) than the corresponding molecules, and are ionized more efficiently. For a given type of secondary species, s, formed on the surface, the resulting positive thermionic emission currents (/) and their dependence on surface temperature (7) are described by the ionization efficiency, Ps(7), and by YXT), the yield of chemical reactions on the surface, such that... 

Stoffels, J.J. (1982). Measurement of iodine-129 at the femtogram level by negative surface ionization mass spectrometry, Radiochem. and Radioanal. Lett. 55, 99. 

A somewhat related technique is that of laser ionization mass spectrometry (LIMS), also known as LIMA and LAMMA, where a single pulsed laser beam ablates material and simultaneously causes some ionization, analogous to samples beyond the outer surface and therefore is more of a bulk analysis technique it also has severe quantiBaction problems, often even more extreme than for SIMS. 

Using the same threshold ionization mass spectrometry setup, Perrin et al. [317] have measured the temporal decay of radical densities in a discharge afterglow. From these experiments the coefficient p for the radical SiH. has been determined to be 0.28, which is in agreement with already known results from other (indirect) experimental approaches [136,137,318]. For the Si2H5 radical is determined to be between 0.1 and 0.3. The coefficient p for atomic hydrogen on a-Si H lies between 0.4 and 1, and is thought to represent mainly surface recombination to H. ... 

Merkel, D., et al., Proteomic study of human bronchoalveolar lavage fluids from smokers with chronic obstructive pulmonary disease by combining surface-enhanced laser desorp-tion/ionization-mass spectrometry profiling with mass spectrometric protein identification, Proteomics. 5, 11, 2972, 2005. 

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. 

Z. Takats, I. Cotte-Rodrfguez, N. Talaty, H. Chen, and R. G. Cooks. Direct, Trace Level Detection of Explosives on Ambient Surfaces by Desorption Electrospray Ionization Mass Spectrometry. Chem. Commun., no. 15 (2005) 1950-1952. 

A laser pulse can ablate material from the surface of a sample, and create a microplasma which ionizes some of the sample components. The laser pulse accomplishes both vaporization and ionization of the sample [366,534,535]. This method is called laser ionization mass spectrometry (LIMS). 

Gardinali PR, Zhao X. 2002. Trace determination of caffeine in surface water samples by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS). Environ Int 28 521. 

Johannesson, N., Wetterhall, M., Markides, K. E., and Bergquist, J. (2004). Monomer surface modifications for rapid peptide analysis by capillary electrophoresis and capillary electrochromatography coupled to electrospray ionization-mass spectrometry. Electrophoresis 25, 809-816. 

Huang, X. A., Zhang, S., Schultz, G. A., and Henion, J., Surface-alkylated polystyrene monolithic columns for peptide analysis in capillary liquid chromatography-electrospray ionization mass spectrometry. Analytical Chemistry 74(10), 2336-2344, 2002. 

Carboxylic acids The smallest carboxylic acid, formic acid, can be measured using infrared spectroscopy (Table 11.2), since it has characteristic absorption bands. As discussed earlier and seen in Fig. 11.33b, mass spectrometry with chemical ionization using SiF5 also revealed HCOOH in an indoor environment (Huey et al., 1998). However, since the sensitivity in these initial studies was about two orders of magnitude less than that for HN03, the detection limit may be about the same as that for FTIR and TDLS. Formic and acetic acids have been monitored continuously from aircraft (Chapman et al., 1995) and their surface flux determined by eddy correlation (Shaw et al., 1998) using atmospheric pressure ionization mass spectrometry. Detection limits are about 30 ppt. 

Depth profiling of single airborne particles has been reported by Carson et al. (1995, 1997a), who showed that the use of variable laser fluences in single-particle laser ionization mass spectrometry can be used to probe thin films on particles in laboratory systems. At low laser intensities, only the surface layer is volatilized and ionized, whereas the entire particle can be vaporized and detected at higher intensities. 

An interesting question is how H3 is formed on the emitter surface and whether H3 molecules can exist on the surface. This question can be investigated with a measurement of the appearance energy of Hj ions. Jason etal.264 find Hj in field ionization of condensed layers of hydrogen, and measure the appearance energy to be 12.7 eV. This value is 2.9 eV smaller than that of H2. Ernst Block conclude265 from a similar measurement in field ionization mass spectrometry of hydrogen that an H 3 ion is formed at the moment when a chemisorbed H atom combines... 

Early field ion emission studies of gas-surface interactions use field ionization mass spectrometry. Gas molecules are supplied continuously to the tip surface by a polarization force and by the hopping motion of the molecules on the tip surface and along the tip shank. These molecules are subsequently field ionized. The role of the emitter surface in chemical reactions is not transparent and has not been investigated in detail. Only in recent pulsed-laser stimulated field desorption studies with atom-probes are these questions addressed in detail. We now discuss briefly a preliminary study of reaction intermediates in NH3 formation in pulsed-laser stimulated field desorption of co-adsorbed hydrogen and nitrogen,... 

Resonance ionization mass spectrometry (RIMS) is much more efficient at getting ions into the detectors. First, atoms are removed from the sample surface with a pulsed laser, which can release the atoms thermally without ionizing them. Then, by using carefully tuned lasers, the element of interest in the resulting gas plume can be ionized at almost 100% efficiency, while other elements are not ionized at all. The ions are extracted into a time-of-flight... 

Mattem GC, Louis JB, Rosen JD. 1991. Multipesticide determination in surface water by gas chromatography/chemical ionization/mass spectrometry/ion trap detection. J Assoc Off Anal Chem 74 982-986... 

The development of laser ionization mass spectrometry was started by Honig and Woolston in 196359 with studies of laser beam sohd surface interaction and ion formation processes. Due to the pulse character of laser-induced ions, ToF analyzers were coupled to laser ion sources in the seventies and produced commercially as LAMMA-500 and later LAMMA-1000 and 2000 (Leybold-Heraeus, Cologne, Germany). 

In contrast, the LA-ICP-MS (in comparison to laser ionization mass spectrometry (LIMS) where the ion source operates under high vacuum conditions) at present, in spite of the disadvantage of a higher polyatomic ion formation rate, uses an argon plasma ionization at normal pressure - a promising inorganic mass spectrometric technique for trace, isotope and surface analysis which will... 

Thermal ionization mass spectrometry (TIMS) is one of the oldest mass spectrometric techniques, first applied by Dempster in 1918.114 The thermal emission of positivly charged ions emitted from a salt on a heated surface was first observed by Gehrcke and Reichenheim 12 years before.115 The thermal surface ionization source is a very simple ion source and operates under high vacuum conditions. TIMS is mostly useful for elements with relatively low ionization energy ( )) - in... 

Martin, C.J., Al, T.A. and Cabri, L.J. (1997) Surface analysis of particles in mine tailings by time-of-flight laser-ionization mass spectrometry (TOF-LIMS). Environmental Geology, 32(2), 107-13. 

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