Laser microprobe mass analyser

For any true microspectrochemical analysis a microscope and a dispersing instrument are needed. An essential feature of a laser microscope is that the objectives for both the observation of the specimen and for focusing the laser radiation must be suitable for ablation, vaporisation, and excitation of the material. The defining attribute of LMMS is the use of a high power pulsed UV laser ultimately focused down to the dil action-limited spot (0.5 ixm at 266 nm) to vaporise, atomise, and ionise a microvolume of a solid specimen in a one-step procedure. Laser microprobe mass analysers are typically equipped with Nd YAG lasers (1064 and 266 nm 5-15 ns pulses) or excimer lasers (XeF, 351 nm XeCl, 308 nm KrF, 248 nm with about 7-30 nm pulses). Power densities of up to 10 Wcm 2 are quite common organic compounds require attenuation to about 10 -10 W cm . By adjusting the laser power, desorption and ionisation can, to some extent, be selected over ablation and dissociation in the microplasma. 

Schmidt PF, Ilsemann K (1984) Quantitation of laser-microprobe-mass-analyses results by the use of organic mass peaks for internal standards. Scanning Electron Microsc 1 77-85. 

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].

The technique is referred to by several acronyms including LAMMA (Laser Microprobe Mass Analysis), LIMA (Laser Ionisation Mass Analysis), and LIMS (Laser Ionisation Mass Spectrometry). It provides a sensitive elemental and/or molecular detection capability which can be used for materials such as semiconductor devices, integrated optical components, alloys, ceramic composites as well as biological materials. The unique microanalytical capabilities that the technique provides in comparison with SIMS, AES and EPMA are that it provides a rapid, sensitive, elemental survey microanalysis, that it is able to analyse electrically insulating materials and that it has the potential for providing molecular or chemical bonding information from the analytical volume. 

The technique based on laser-induced breakdown coupled to mass detection, which should thus be designated LIB-MS, is better known as laser plasma ionization mass spectrometry (LI-MS). The earliest uses of the laser-mass spectrometry couple were reported in the late 1960s. Early work included the vaporization of graphite and coal for classifying coals, elemental analyses in metals, isotope ratio measurements and pyrolysis [192]. Later work extended these methods to biological samples, the development of the laser microprobe mass spectrometer, the formation of molecular ions from non-voIatile organic salts and the many multi-photon techniques designed for (mainly) molecular analysis [192]. 

ADA/AKY] Adams, F. C., Akyuz, S., Akyuz, T., De Waele, J. K., Laser microprobe mass (LAMMA) and infrared spectral analyses of the thorium-rare earths mineral from the deposits of eastern Turkey, Hacettepe Bull. Nat. Sci. Eng., 13, (1984), 19-27. 

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... 

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). 

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],... 

Analyses were performed using a modified laser microprobe Fourier transform mass spectrometer (FTMS). This instrument is differentially pumped with a dual-cell Nicolet Instrument FTMS 2000 (Thermoquest, Madison,... 

Figure 1. Advantages and trade-offs of new analytical techniques for stable isotope analysis (see Table 1). At present, the best accuracy and precision is achieved for 5 0 by IR-laser fluorination of chips or powdered samples the fastest and least expensive analyses are made by automated pyrolysis systems with continuous flow mass-spectrometers (CFMS) and the smallest samples and best in situ spatial resolution is attained by ion microprobe. The capabilities of in situ UV-laser fluorination are intermediate.

The diameter of the laser beam used to probe the sample surface typically determines the effective spatial resolution of a measurement performed in microprobe mode. Obviously, the laser beam diameter can be reduced by focusing the beam to smaller dimensions. However, as the laser beam diameter is reduced, it illuminates a smaller area, fewer molecules of each analyte are present within the probe beam, and so fewer molecules are ionized at each location. Therefore, smallest diameter beams are rarely practical because the amount of analyte that can be desorbed and ionized from a smaller sample area is not sufficient for detection and high-accuracy mass measurement. Consequently, the laser probe diameter for the analyses of proteins and peptides usually is larger than 10 xm. 

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