Spectra laser-microprobe

Laser microprobe MS (LMMS) can be used for direct analysis of normal-phase HPTLC plates [802,837]. Kubis et al. [802] used polyamide TLC plates polyamide does not interfere with compound identification by the mass spectrum, owing to its low-mass fragment-ions (m/z < 150). LMMS is essentially a surface analysis technique, in which the sample is ablated using a Nd-YAG laser. The UV irradiation desorbs and ionises a microvolume of the sample the positive and negative ions can be analysed by using a ToF mass spectrometer. The main characteristics of TLC-LMMS are indicated in Table 7.84 [838],... 

A rather specialized emission source, which is applicable to the study of small samples or localized areas on a larger one, is the laser microprobe. A pulsed ruby laser beam is focused onto the surface of the sample to produce a signal from a localized area ca. 50 pm in diameter. The spectrum produced is similar to that produced by arc/spark sources and is processed by similar optical systems. 

Conditions used to acquire the microprobe spectrum laser -514.5nm, S.Smw at sanple) Slits, 300 m. Scan rate lOOarTVmin Ooaddition of 3 scans Objective 80x. 

Laser microprobe mass analysis/ LAMMA, 1 pm Mass spectrum AH elements Laser excitation Reproducibility 105... 

Figure 11 Identification of the interaction products between the triethanolamine oleate additive of a lubricating emulsion and rolled aluminum. Top positive ion mass spectrum recorded using FT-LMMS with an external ion source. Bottom structural assignment of the ions of major diagnostic interest. The corresponding high accuracy miz data are listed in Table 2. The framed structures are indicative of the binding of the additive to aluminum. (Reprinted from Poels K, Van Vaeck L, Van Espen P, Terryn H, and Adams F (1996) Feasibility of Fourier transform laser microprobe mass spectrometry for the analysis of lubricating emulsions on rolled aluminum. Rapid Communications in Mass Spectrometry W 1351-1360 Wiley.)...

Figure 6 Positive ion mass spectrum of high-purity GaAs recorded with TOF-LMMS without (A) and with (B) postionization. (Reprinted from Schueler B and Odom R (1987) Nonresonant multiphoton ionisation of the neutrals ablated In laser microprobe mass spectrometry analysis of GaAs and Hgo.78Cdo.22Te. Journal of Applied Physics 61 4652-4661.)...

Figure 3 Third dimension in pyrolysis mass spectrometry approaches (A) linear programmed thermal degradation mass spectrometry [LPTDMS - third dimension = temperature] (B) collisionally activated dissociation of parent ions coupled with scanning of product ions using tandem mass spectrometry [MS/ MS - third dimension = spectrum of product ions] (C) laser microprobe mass analyser [LAMMA - third dimension = spatial resolution].

Microprobe laser desorption laser ionisation mass spectrometry (/xL2MS) is used to provide spatial resolution and identification of organic molecules across a meteorite sample. Tracking the chemical composition across the surface of the meteorite requires a full mass spectrum to be measured every 10 p,m across the surface. The molecules must be desorbed from the surface with minimal disruption to their chemical structure to prevent fragmentation so that the mass spectrum consists principally of parent ions. Ideally, the conventional electron bombardment ionisation technique can be replaced with an ionisation that is selective to the carbonaceous species of interest to simplify the mass spectrum. Most information will be obtained if small samples are used so that sensitivity levels should be lower than attomolar (10—18 M) fewer than 1000 molecules can be detected and above all it must be certain that the molecules came from the sample and are not introduced by the instrument itself. 

Figure 3-8 Raman microprobe spectrum of fluorinated hydrocarbon contaminant on silicon wafer that had been polished and plasma-etched (lower) and Raman spectrum of polytetrafluoro-ethylene (upper). Laser, 135 mW at 514.5 nm. Slits, 300 jon. Time, 0.5 s per data point. (Reproduced with permission from Adar, F., in Microelectronics Processing Inorganic Materials Characterization (L. A. Casper, ed.), ACS Symposium Series Vol. 295, pp. 230-239. American Chemical Society, Washington, D.C., 1986. Copyright 1986 American Chemical Society.)...

The surface morphology, thickness and quality of the deposited carbon films are analyzed by scanning electron microscopy (SEM), by energy dispersive x-ray (EDx) and by Raman spectroscopy (RS). The Raman spectrum was recorded using an argon ion laser Raman microprobe. The exciting laser wavelength is 632.81 nm with a laser power equal to 1.75 mW. The instrument was operated in the multi-channel mode with the beam focused to a spot diameter of approximately 2 pm. 

Small area Infrared anal ls produced the spectrum In Figure 10 the absorption at 1400cm was Interpreted as basic lead carbonate. This was also confirmed by electron diffraction of the same crystals. Raman microprobe gave conflicting data because the lead carbonate decomposed under the laser beam, giving a mixture of "daughter" products (mixtures constitute a "real world" analytical problem). 

Laser Raman Microprobe This allows information to be collected from small samples via the use of a VLM, which allows the region to be selected from which the Raman spectrum will be obtained. Surface-Enhanced Raman Scattering (SERS) This is used to examine surfaces, oxidation, catalysis, and thin films. 

Nondestructive analysis of various materials, such as rocks, composite materials, phases and inclusion in solids, can be performed with a laser molecular microprobe [8.70], which is based on a combination of an optical microscope with a Raman spectrometer. The laser beam is focused into the sample and the Raman spectrum, emitted from the smal focal spot, is mon-... 

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