Laser vaporization mass spectrometry

Bonnell, D.W. Schenck, P.K. Hastie, J.W. Joseph, M. "Ultra-High Temperature Laser Vaporization Mass Spectrometry of SiC and Hf02" In 5th Inti, Symposium on High Temperature Materials Chemistry Johnson, W.B., Rapp, R.A., Eds. ECS Symp. Vol. PV90-18 Electrochemical Society Pennington, NJ, 1990 156-165. 

In Laser Ionization Mass Spectrometry (LIMS, also LAMMA, LAMMS, and LIMA), a vacuum-compatible solid sample is irradiated with short pulses ("10 ns) of ultraviolet laser light. The laser pulse vaporizes a microvolume of material, and a fraction of the vaporized species are ionized and accelerated into a time-of-flight mass spectrometer which measures the signal intensity of the mass-separated ions. The instrument acquires a complete mass spectrum, typically covering the range 0— 250 atomic mass units (amu), with each laser pulse. A survey analysis of the material is performed in this way. The relative intensities of the signals can be converted to concentrations with the use of appropriate standards, and quantitative or semi-quantitative analyses are possible with the use of such standards. 

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). 

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. 

Among the other soft ionization techniques is laser microprobe mass spectrometry (LAMMA) in which a laser pulse is used to vaporize a small amount of sample, as discussed in a 1982 review (108). Of interest to us is the application to the study of some cobalamins (109). (M + H) and (M - H) ions were observed in the positive and negative ion modes, respectively. However, there were few other high-mass fragments that could be used to impart structural information. 

Hastie, John W., D. W. Bonnell, P. K. Schenck, and National Institute of Standards and Technology (U.S.). Laser-Assisted Vaporization Mass Spectrometry Application to Thermochemistry at Very High Temperatures. NISTIR, 6793. Gaithersburg, Md. U.S. Dept, of Commerce, Technology Administration, National Institute of Standards and Technology, 2001. 

Fig. 1.29. Schematic sketch of the collision cell method for the study of metal cluster reactivity. The supersonic laser vaporization source is depicted on the right hand side. The clusters subsequently pass two collision cells in which reactions can take place. Finally, laser ionization mass spectrometry serves to detect the neutral reaction products [3]...

Limitations to high-temperature materials chemistry research due to the non-availability of suitable container materials have been overcome by laser induced vaporization mass spectrometry (see e.g. Ref. 587). This technique couples laser heating of refractory materials under vacuum with the mass spectrometric analysis of the vapor plume. Hastie et al. [588] have recently investigated the vaporization of graphite by this technique. The investigations by Ohse s group on the laser induced vaporization of fast breeder oxide and carbide fuels should also be mentioned in this context (see Refs. 589, 590 and references quoted therein). 

Laser desorption is commonly used for pyrolysis/mass spectrometry, in which small samples are heated very rapidly to high temperatures to vaporize them before they are ionized. In this application of lasers, very small samples are used, and the intention is not simply to vaporize intact molecules but also to cause characteristic degradation. 

The previous discussion has centered on how to obtain as much molecular mass and chemical structure information as possible from a given sample. However, there are many uses of mass spectrometry where precise isotope ratios are needed and total molecular mass information is unimportant. For accurate measurement of isotope ratio, the sample can be vaporized and then directed into a plasma torch. The sample can be a gas or a solution that is vaporized to form an aerosol, or it can be a solid that is vaporized to an aerosol by laser ablation. Whatever method is used to vaporize the sample, it is then swept into the flame of a plasma torch. Operating at temperatures of about 5000 K and containing large numbers of gas ions and electrons, the plasma completely fragments all substances into ionized atoms within a few milliseconds. The ionized atoms are then passed into a mass analyzer for measurement of their atomic mass and abundance of isotopes. Even intractable substances such as glass, ceramics, rock, and bone can be examined directly by this technique. 

The molecular weights and molecular weight distributions (MWD) of phenolic oligomers have been evaluated using gel permeation chromatography (GPC),23,24 NMR spectroscopy,25 vapor pressure osmometry (VPO),26 intrinsic viscosity,27 and more recently matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).28... 

There are several methods in use for producing these clusters. Particle bombardment or laser vaporization of a graphite surface leads to direct formation of ions that can be detected by mass spectrometry. These are normally of relatively small size (n<30). By laser vaporization of graphite into a molecular beam neutral... 

In this paper, the photofragmentation of transition metal cluster complexes is discussed. The experimental information presented concerning the gas phase photodissociation of transition metal cluster complexes comes from laser photolysis followed by detection of fragments by ionization (5.). Ion counting techniques are used for detection because they are extremely sensitive and therefore suitable for the study of molecules with very low vapor pressures (6.26.27). In addition, ionization techniques allow the use of mass spectrometry for unambiguous identification of signal carriers. 

Mass spectrometry requires that the material being studied be converted into a vapor. Great strides have been taken in recent years to address this problem, especially in enticing large, thermally fragile (bio)molecules into the vapor state. Matrix assisted laser ionization-desorption (MALDI) and electrospray ionization (ESI) are two current forefront methods that accomplish this task. Even components of bacteria and intact viruses are being examined with these approaches. John B. Fenn and Koichi Tanaka shared in the award of a Nobel Prize in 2002 for their respective contributions to development of electrospray ionization and soft laser desorption. 

In 1984 it was observed that, upon laser vaporization of graphite, large carbon-only clusters C with u = 30-190 can be produced [14]. The mass distribution of these clusters was determined by time-of-flight mass spectrometry. Only ions with... 

The book includes several chapters on vapor and trace detection chemiluminescence, mass spectrometry, ion mobility spectrometry, electrochemical methods, and micro mechanical sensors, such as microcantilevers. Other chapters deal with bulk detection techniques neutron techniques, nuclear quadrupole resonance, X-ray diffraction imaging, millimeter-wave imaging, terahertz imaging, and laser techniques. Special chapters are devoted to personnel portals and to biological detection. 

Most of the mass spectrometry applications for combinatorial chemistry will be described in the following sections of this chapter. Here we will give a short overview of MS techniques utilized for the characterization of resin-bound molecules. The majority of publications in this field describe applications of matrix-assisted laser desorption ionization (MALDI), combined with time-of-flight (TOF) detection. The major difference of MS application for analysis of resin-bound molecules from the above-described NMR and IR applications is that analyte should not be covalently bound to solid support prior to mass measurement. Detachment of compound molecules from resin can be done chemically (for example, by bead exposure to TFA vapors) [30,31] or photochemically, such that cleavage, desorption, and ionization of molecules occur simultaneously upon stimulation by laser radiation [32], Since the... 

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