Laser analytical procedures

An analytical procedure has been proposed for precise uranium isotope ratio measurements in a thin uranium layer on a biological surface by LA-ICP-MS using a cooled laser ablation chamber.125 One drop of uranium isotope standard reference materials NIST, 350, NIST 930, of our isotopic laboratory standard CCLU 500 (20p.l, U concentration 200 ng 1) and of uranium with natural isotopic pattern were deposited on the leaf surface and analyzed by LA-ICP-MS at well defined laser crater diameters of 10, 15, 25 and 50 p.m. A precision for measurements of isotope ratios in the range of 2.1-1.0% for 235U/238U in selected isotope standards was observed whereby the precision and the accuracy of isotope ratios compared to the non-cooled laser ablation chamber was improved.125... 

The requirements for chemical actinometers, listed in the previous sections [such as sensitivity, reproducibility, (thermal) stability, ease of analytical procedure, etc.], reduce the seemingly unlimited number of actinometers reported over the years (9) to a short list of well-established and highly recommended chemical actinometers. In this section, we first present a selected list of such reliable actinometers, which all operate in the liquid phase. After that, a few controversial systems are described and their potential error sources discussed. Finally, actinometric procedures suitable for solid-state applications, polychromatic sources, and laser irradiation will be introduced in section "Special Applications."... 

The hnished product will be subjected to inspection and rigorous testing for identity, uniformity, residual water content, stability, sterility and potency. In addition, all analytical techniques employed in testing these attributes will themselves have been subjected for reliability, reproducibility, experimental uncertainty limits. The biotechnological revolution has resulted in the appearance of ever more rehned and sensitive analytical techniques, mainly novel types of spectroscopy and coupled techniques, based on mass spectrometry, known usually by complex acronyms, e.g. MALDI-TOE-MS (Matrix-Assisted-Laser-Z)esorption-71me-of-Tlight-Mass Spectrometry). Some of the available analytical procedures are treated in more detail in the next chapter. 

This chapter considers the quantitative aspects of single-molecule detection in solution by laser-induced fluorescence. We will describe the combination of single molecule detection with capillary electrophoresis as the ultimate analytical procedure. Other methods of single molecule detection, such as electrochemical detection, are not considered [1, 2]. 

This review provides an up-to-date overview of the application of analytical procedures based on MS for the characterization of organic natural materials in archaeological and historical objects. Applications that feature the use of gas chromatography/mass spectrometry (GC/MS), Py-GC/MS, high performance liquid chromatography combined with mass spectrometry (HPLC/MS), and direct MS analysis such as matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), electrospray ionization mass spectrometry (ESI-MS), and direct exposure mass spectrometry (DE-MS) are sununarized to highlight the different information provided by each of the various analytical approaches. Case studies and examples are also presented and include a description of the molecular markers and of the molecular profiles that are used to identify the original materials. 

Technetium isotopes in the PWR primary coolant show a behavior which is quite different from that of the other fission products treated in this section. Whereas the short-lived Tc is only of minor radiological relevance, its long-lived isomer c (halflife 2.1 HP a) deserves some attention with respect to safety analyses for the final storage of radioactive wastes. Normally, c is not analyzed in the reactor coolant because of its very low activity concentration and of its unfavorable radiation properties (P 0.3 MeV, negligible y transition). For this reason, the Tc mass is frequently determined rather than its radioactivity suitable techniques for this task are neutron activation analysis, inductively-coupled mass spectrometry and laser resonance ionization mass spectrometry (see, for example, the comparative evaluation given by Trautmann, 1993). In each case, very expensive analytical procedures are required therefore, the greatest part of the available information on Tc behavior in reactor primary circuits has been derived from measurements of y-emitting Tc. 

In 1996 we described (1) the successful application of Matrix-Assisted-Laser-Desorption/Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF-MS) for characterizing hemicelluloses isolated from wood and pulps. Since then this approach has been improved considerably (2,3) and several different procedures for wood and pulp constituents have been reported (3-8). In the present article, a selection of our previously reported analytical procedures are discussed together with some hitherto unpublished results from our laboratory. 

Analytical procedures for foods are generally based on extraction with purified solvents following saponification with alcoholic potash. Purification of the extracts by chromatography on column or plates is followed by analysis of the purified extract using TLC, GLC or HPLC. Spectrophotometric or spectrofluorimetric methods may be used for quantitation of the hydrocarbons a collaborative study of a spectrophotometric method showed it to be applicable at the 2 fig/kg level. HPLC techniques using spectrofluorimetric detection have been described for which improved levels of detection are claimed. Benzo(a)pyrene produces substitution products with nucleic acids. Hydrocarbon deoxyribonucleoside adducts may be isolated from DNA by gel permeation chromatography, and the formation of hydrocarbon epoxides by mammalian enzyme reaction has also been demonstrated . The limit of detection of spectrophotometric and fluorimetric methods has been improved by three orders of magnitude by the use of laser-induced fluorescence procedures for the... 

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