Spectrometry, mass laser probe

Very promising is the development of a laser probe mass analyzer for metal analysis of high spatial resolution Foils or thin sections of less than 2 fita are evaporated and ionized by pulsed laser beams in vacuum. Lasers (rubin or Nd-YAG) with power densities between 10 and 10 W/cm produce, when optimally focused, a spatial resolution higher than 1 /tm. Time-of-flight or double focusing instnunents are used for mass analysis. 

The laser ion source can be used for trace analysis of all elements down to the sub-ppm range. The main advantage of this method compared with spark source mass spectrometry is that little sample preparation is required so that minute sample amounts which are difficult to handle can be investigated. A mixture of the sample with the conducting material, such as graphite is not necesseny, because the conductivity of the sample has no influence on the ion production. 

The spot of sample analysis can be varied by manipulation of the sample so that the distribution of an element in the sample can be examined. The laser probe mass spectrum recorded by Heinen et al. (Fig. 9) illustrates the determination of iron traces in a cell of an uterus gland of a pregnant animal. 

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Fig. 9. Distribution of iron in a cell of an uterus gland determined by laser probe mass spectrometry , a Mass spectra of various sample spots diminished by the background spectrum, b Abundance profile of iron along the gland cell...

Laser ionization mass spectrometry or laser microprobing (LIMS) is a microanalyt-ical technique used to rapidly characterize the elemental and, sometimes, molecular composition of materials. It is based on the ability of short high-power laser pulses (-10 ns) to produce ions from solids. The ions formed in these brief pulses are analyzed using a time-of-flight mass spectrometer. The quasi-simultaneous collection of all ion masses allows the survey analysis of unknown materials. The main applications of LIMS are in failure analysis, where chemical differences between a contaminated sample and a control need to be rapidly assessed. The ability to focus the laser beam to a diameter of approximately 1 mm permits the application of this technique to the characterization of small features, for example, in integrated circuits. The LIMS detection limits for many elements are close to 10 at/cm, which makes this technique considerably more sensitive than other survey microan-alytical techniques, such as Auger Electron Spectroscopy (AES) or Electron Probe Microanalysis (EPMA). Additionally, LIMS can be used to analyze insulating sam-... 

In order to relate material properties with plasma properties, several plasma diagnostic techniques are used. The main techniques for the characterization of silane-hydrogen deposition plasmas are optical spectroscopy, electrostatic probes, mass spectrometry, and ellipsometry [117, 286]. Optical emission spectroscopy (OES) is a noninvasive technique and has been developed for identification of Si, SiH, Si+, and species in the plasma. Active spectroscopy, such as laser induced fluorescence (LIF), also allows for the detection of radicals in the plasma. Mass spectrometry enables the study of ion and radical chemistry in the discharge, either ex situ or in situ. The Langmuir probe technique is simple and very suitable for measuring plasma characteristics in nonreactive plasmas. In case of silane plasma it can be used, but it is difficult. Ellipsometry is used to follow the deposition process in situ. 

Infrared and ultraviolet probes for surface analysis are then considered.The applications of IR spectroscopy and Raman microscopy are discussed, and a brief account is also given of laser-microprobe mass spectrometry (LAMMA). 

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. 

We have developed an analogous, but more robust system which is not necessarily constraint by the aforementioned limitations. The obvious extension has been to couple an affinity-based separation with mass spectrometry. Hutchens et al. have shown that affinity probe surfaces can be ust to capture specific protein ligands allowing detection by laser desorption mass spectrometry (. The limitations to their technique have been that the surface area for ligand capture is quite small and salt (or detergent) contaminants are still problematic. Perfusive affinity resins, on the other hand, provide a tremendous surface area for binding. The nature and composition of the solvents required for affinity chromatography, however, are not directly compatible with mass spectrometric analysis. 

Then, the thin films are characterised by matrix assisted laser desorption mass spectrometry and scanning probe microscopic techniques. In the case of unsubstituted HBC scanning tunnelling microscopy revealed the formation of ordered nanoscale semiconducting supramolecular architectures at the surface of HOPG [39] (Figure 4.12a). The arrangement of HBC at the surface is charac-... 

Microprobe techniques, and their detection limits (given in mgkg ), that have been applied to Al localization include energy dispersive (electron probe) X-ray microanalysis (20), wavelength-dispersive X-ray microanalysis, electron energy loss spectrometry (500), proton probe nuclear microscopy (10), resonance ionization mass spectrometry (3), secondary ion mass spectrometry (1), laser microprobe mass spectrometry (1) and micropartide-induced X-ray emission (Yokel 2000). 

An example of this is shown in Figure 15 for a poly(methyl methacrylate)/polystyrene laminate. Data from a 6 x 6 array of pyrolysis measurements were used to reconstruct images based upon the ion yield of the respective monomers. Unlike similar methods of chemical imaging (e.g. secondary ion mass spectrometry and laser ionisation mass spectrometry), the sample is examined under ambient conditions rather than high vacuum [167]. Three-dimensional tomographic imaging may also be considered by using the probe to ablate the surface. 

Optical microscopy (OM), polarized light microscopy (PLM), phase contrast microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) are the methods normally used for identification and quantification of the trace amounts of asbestos fibers that are encountered in the environment and lung tissue. Energy-dispersive X-ray spectrometry (EDXS) is used in both SEM and TEM for chemical analysis of individual particles, while selected-area electron diffraction (SAED) pattern analysis in TEM can provide details of the cell unit of individual particles of mass down to 10 g. It helps to differentiate between antigorite and chrysotile. Secondary ion mass spectrometry, laser microprobe mass spectrometry (EMMS), electron probe X-ray microanalysis (EPXMA), and X-ray photoelectron spectroscopy (XPS) are also analytical techniques used for asbestos chemical characterization. 

Principles and Characteristics Laser microprobe mass spectrometry (LMMS, LAMMS), sometimes called laser probe microanalysis (LPA or LPMA) and often also referred to as laser microprobe mass analysis (LAMMA , Leybold Heraeus) [317] or laser ionisation mass analysis (LIMA , Cambridge Mass Spectrome-try/Kratos) [318], both being registered trademarks, is part of the wider laser ionisation mass spectrometry (LIMS) family. In the original laser microprobe analyser, emitted light was dispersed in a polychro-mator. Improved sensitivity may be obtained by secondary excitation of ablated species with an electric spark. In the mass spectrometric version of the laser microprobe, ions formed in the microplasma... 

Although a combination of spectroscopy imaging e.g. /xXRF, /xFTIR, /xRS) would offer a powerful way to characterise materials various hurdles must be overcome to achieve the ultimate in integrated spectroscopic imaging. These difficulties include spatial resolution, specimen preparation, spectroscopic probe penetration depth and image integration. Same-spot (optical, /u-FTIR, /u.RS) technology is now available. The topic of Raman microscopy in combination with other microanalysis techniques (electron microscopy/X-ray microanalysis ion mi-croprobe mass spectrometry, and laser microprobe mass spectrometry), i.e. dual-use microprobe systems, has been discussed [534]. 

The defining attribute of laser microprobe mass spectrometry (LMMS) is the use of a focused laser to irradiate a 5- 10 pm spot of a solid sample at a power density above 10 W cm. The photon solid interaction yields ions which are mass analysed by time of-flight (TOF) or Fourier transform (FT) MS. The technique is sometimes referred to as laser probe microanalysis (LPA or LPMA), laser ionization mass analysis (LIMA) and laser microprobe mass analysis (LAMMA). 

Spengler, B. Kaufmann, R. Gentle probe for tough molecules Matrix-assisted laser desorption mass spectrometry. Analusis 1992, 20, 91-101. 

Jeffries TE, Perkins WT, Pearce NJG (1995) Measmements of trace elements in basalts and their phenocrysts by laser probe microanalysis indnctively conpled plasma mass spectrometry. Chem Geol 121 131-144... 

For non-volatile sample molecules, other ionisation methods must be used, namely desorption/ionisation (DI) and nebulisation ionisation methods. In DI, the unifying aspect is the rapid addition of energy into a condensed-phase sample, with subsequent generation and release of ions into the mass analyser. In El and Cl, the processes of volatilisation and ionisation are distinct and separable in DI, they are intimately associated. In nebulisation ionisation, such as ESP or TSP, an aerosol spray is used at some stage to separate sample molecules and/or ions from the solvent liquid that carries them into the source of the mass spectrometer. Less volatile but thermally stable compounds can be thermally vaporised in the direct inlet probe (DIP) situated close to the ionising molecular beam. This DIP is standard equipment on most instruments an El spectrum results. Techniques that extend the utility of mass spectrometry to the least volatile and more labile organic molecules include FD, EHD, surface ionisation (SIMS, FAB) and matrix-assisted laser desorption (MALD) as the last... 

If we consider only a few of the general requirements for the ideal polymer/additive analysis techniques (e.g. no matrix interferences, quantitative), then it is obvious that the choice is much restricted. Elements of the ideal method might include LD and MS, with reference to CRMs. Laser desorption and REMPI-MS are moving closest to direct selective sampling tandem mass spectrometry is supreme in identification. Direct-probe MS may yield accurate masses and concentrations of the components contained in the polymeric material. Selective sample preparation, efficient separation, selective detection, mass spectrometry and chemometric deconvolution techniques are complementary rather than competitive techniques. For elemental analysis, LA-ICP-ToFMS scores high. 

Madonna, A. I Basile, F. Imma, I. Meetani, A. M. Rees, J. C. Voorhees, K. J. On-probe sample pretreatment for the detection of proteins above 15 KDa from whole cell bacteria by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Rapid Comm. Mass Spectrom. 2000,14, 2220-2229. 

There are now several different types of machines that are all capable of microanalysis. All have advantages and disadvantages, but the choice of which to use is often governed by expense and availability to a particular institution. Electron probe microanalysis is by far the most popular, but here particle-induced X-ray emission (PIXE), the laser microprobe mass analyzer (LAMMA), electron energy loss spectroscopy (EELS), and secondary ion mass spectrometry (SIMS) are also considered. 

DGE a AC AMS APCI API AP-MALDI APPI ASAP BIRD c CAD CE CF CF-FAB Cl CID cw CZE Da DAPCI DART DC DE DESI DIOS DTIMS EC ECD El ELDI EM ESI ETD eV f FAB FAIMS FD FI FT FTICR two-dimensional gel electrophoresis atto, 10 18 alternating current accelerator mass spectrometry atmospheric pressure chemical ionization atmospheric pressure ionization atmospheric pressure matrix-assisted laser desorption/ionization atmospheric pressure photoionization atmospheric-pressure solids analysis probe blackbody infrared radiative dissociation centi, 10-2 collision-activated dissociation capillary electrophoresis continuous flow continuous flow fast atom bombardment chemical ionization collision-induced dissociation continuous wave capillary zone electrophoresis dalton desorption atmospheric pressure chemical ionization direct analysis in real time direct current delayed extraction desorption electrospray ionization desorption/ionization on silicon drift tube ion mobility spectrometry electrochromatography electron capture dissociation electron ionization electrospray-assisted laser desorption/ionization electron multiplier electrospray ionization electron transfer dissociation electron volt femto, 1CT15 fast atom bombardment field asymmetric waveform ion mobility spectrometry field desorption field ionization Fourier transform Fourier transform ion cyclotron resonance... 

The pump and probe pulses employed may be subjected to a variety of nonlinear optical mixing processes they may be prepared and characterized by intensity, duration, spectral band width, and polarization. They may arrive in the reaction chamber at a desired time difference, or none. The probe pulse may lead to ionizations followed by detections of ions by mass spectrometry, but many alternatives for probing and detection have been used, such as laser-induced fluorescence, photoelectron spectroscopic detection, absorption spectroscopy, and the like. 

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