Chemical characterization integrated spectrometry

The chemical aspects of these studies focus primarily on the chemical characterization of the test substance and/or mixture. The identity of the test chemical should be proven, and the analytical procedures used, such as gas or liquid chromatography, nuclear magnetic resonance spectrometry, or nass spectroscopy, should be available for audit. This would include the chromatograms or spectra from these analyses. It is imperative that raw data be left intact as they emerge from an instrument to maintain data integrity. Chro-natographic printouts are to remain attached and in sequence. If some data points are not used in the final report, the reason is to be documented and those not used are to remain with the stud/ file. 

The chemical characterization of forensic evidence from a crime scene or the criminal has some different requirements from that of many other types of chemical analysis. High sensitivity is important because the quantity of material for examination is often limited to minute traces found at the scene. The material under scrutiny must be characterized as comprehensively as possible to ensure maximum discrimination from other material in the same class. Forensic laboratories are multiinstrument facilities required to deal with many types of evidence found at a crime scene therefore, the routine methods used should preferably employ relatively inexpensive instrumentation. In order to protect integrity, samples should be analyzed as received if possible and any workup minimized. The method should preferably not be labor intensive. Pyrolysis-gas chromatography (Py-GC) and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) have proven to be an effective means of satisfying these requirements in many forensic science laboratories. - ... 

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-... 

Contemporary approaches to chemical stmcture elucidation are now heavily reliant on mass spectrometry and NMR spectroscopy. Since the advent of 2D NMR methods, in many laboratories vibrational data are either not acquired or not considered, which represents a paradigm shift from approaches to chemical structure elucidation as recently as 20 years ago when vibrational spectroscopic data were an integral part of the structure elucidation data assembled to characterize an unknown structure. In contrast, we have found it useful to continue to acquire and utilize vibrational data for the characterization of impurities and degradation products [64,65]. 

It is generally desirable to integrate measurements representing a working catalyst surface with measurements that characterize the activity, selectivity, and/or stability of the catalyst, such as can be determined by use of gas chromatography or mass spectrometry of products. It is important to keep in mind that when a reactor is designed to serve optimally as a cell for measurements of catalyst surface properties, it may not be the kind of ideal reactor that would provide activity, selectivity, or stability data that can be interpreted fundamentally in terms of kinetics and chemical reaction engineering. 

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