Laser sampling

Although iastmmentation is discussed ia many of the analytical articles, there are only a few places ia the Eniyclopedia where it is the primary emphasis (see Analytical methods, hyphenated instruments Automated instrumentation). However, articles relating to materials used either ia or as iastmmeatal compoaeats such as eaergy sources (see Lasers), sampling devices (see Eiber optics), and detectors (see Biosensors Photodetectors SsENSORs) abound. 

Laser sampling is more a physical phenomenon than a chemical one. The energy of the laser is used to nonselectively ablate the sample. This insures homogeneous sampling of a physically defined area regardless of the nature of the components Solubilities are not a factor. This technique shows much promise for ceramics, glasses, and geologic samples. 

Ultrasensitive Equipment In recent years all components of Raman equipment (laser, sampling optics, filtering, monochromator, and detector) have been clearly improved. This has led to an enormous increase in sensitivity and has enabled direct observation of adsorbed molecules with carefully optimized instruments without the need for further enhancement or resonance effects. 

Tuff (rock sample) 5 Vm and 200/im Fig. 5. Tuff sample with several laser sampled locations. 

Gratuze, B., Blet-Lemarquand, M. and Barrandon, J.N. (2001). Mass spectrometry with laser sampling a new tool to characterize archaeological materials. Journal of Radio analytical and Nuclear Chemistry 247 645-656. 

Laser Neutral Laser Sample Annulus Relay Field... 

Fig. 6.12. Data obtained by the single-photon wavelength 340 nm observation wavelength timing technique using a mode-locked ion- 390 nm. Reference scattering solution argon laser that synchronously pumps a cavity- (Ludox). Number of channels 900 channel dumped dye laser. Sample solution of POPOP width 4.68 ps. Result t = 1.05 + 0.01 ns in cyclohexane (undegassed). Excitation x = 1.055.

Broadhead, M., Broadhead, R., and Hager, J.W. (1990) Laser sampling ICP-MS semi-quantitative determination of sixty-six elements in geological samples. Atomic Spectroscopy 11, 205-209. 

The speed of MALDI analysis depends on the laser pulse rate. With the recent introduction of 200-Hz lasers, samples can be analyzed ten times faster than before. This development is especially advantageous for offline liquid chromatography (LC)/MALDI applications (Ericson et al., 2003). MALDI mass analysis is performed considerably faster than LC separation, allowing for chromatographic... 

Eggins S. M., Kinsley L. P. J., and Shelley J. M. M. (1998) Deposition and element fractionation processes during atmospheric pressure laser sampling for analysis by ICPMS. Appl. Surf. Sci. 127-129, 278-286. 

The lack of homogeneity of the sample is a major source of variance. The laser samples an average area of 1 mm% which is not sampled uniformly as different parts are exposed to different temperatures. A routine measurement typically involves about 100 laser pulses, so the examined area is in the region of 1 cm-. Inhomogeneities influence laser absorption, the mass ablated and the plasma conditions. On the other hand, there can also be substantial inhomogeneities in the standard reference samples that will pose problems with analyses. These problems become even more severe if the laser is focused more tightly in order to sample smaller amounts of material. 

A pragmatic disadvantage of the 90° geometry relates to the alignment of laser, sample, and collection optics. For the 180° geometry, the laser and collection axes are coincident, so the sample position cannot affect their... 

Koch J., Miclea M. and Niemax K. (1999) Analysis of chlorine in polymers by laser sampling and diode-laser atomic absorption spectrometry Spectrochim Acta, Part B 54 1723-1735. 

Matrix-assisted laser Sample in crystalline matrix Higher fragmentation level than ESI,... 

The laser beam efficiently vaporizes conductors, insulators, and semiconducting materials with a minimum of matrix effects. Laser sampling ICP-MS has also been applied successfully as a semi-quantitative survey tool for a rapid multi-element analysis of geological samples. The samples are pulverized to assure homogeneity. Some paraffin wax is mixed with the sample. The mixture is then placed in an aluminium cup and pressed into a wafer. 

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