Mass spectrometry case studies

Heck, A.J.R. Derrick, P.J. Ultrahigh mass accuracy in isotope selective collision-induced dissociation using correlated sweep excitation and sustained off resonance iradiation A Fourier transform mass spectrometry case study on the [M + 2H]2-t ion of bradykinin. Anal. Chem. 1997, 69, 3603-3607. 

Fahhri, D. Use of pyrolysis-gas chromatography/mass spectrometry to study environmental pollution caused by synthetic polymers A case study The Ravenna lagoon. J. Anal. Appl. Pyrol. 2001, 58-59, 361-370. 

Proteomic analysis frequently involves comparison of protein levels in experimental and control samples, which is linked with the quantitative analysis (see Chapter 8). In some cases, it is necessary to follow protein abundances over time. Changes in protein levels in cells or biofluids may be monitored over a few hours or days, which does not put much pressure on the temporal resolution of the analytical procedure [at least not to the extent observed in ultrafast time-resolved mass spectrometry (TRMS) studies introduced in other chapters of this book]. LC-MS is a simple approach to obtain relative abundances of proteins in highly complex samples [30]. It is possible to carry out quantitative comparisons... 

The first mass spectrometric investigation of the thiazole ring was done by Clarke et al. (271). Shortly after, Cooks et al., in a study devoted to bicydic aromatic systems, demonstrated the influence of the benzo ring in benzothiazole (272). Since this time, many studies have been devoted to the influence of various types of substitution upon fragmentation schemes and rearrangements, in the case of alkylthiazoles by Buttery (273) arylthiazoles by Aune et al. (276), Rix et al. (277), Khnulnitskii et al. (278) functional derivatives by Salmona el al. (279) and Entenmann (280) and thiazoles isotopically labeled with deuterium and C by Bojesen et al. (113). More recently, Witzhum et al. have detected the presence of simple derivatives of thiazole in food aromas by mass spectrometry (281). 

For marble provenance studies, the most successful technique seems to be the measurement, through mass spectrometry, of the abundance ratios of the stable isotopes of carbon and oxygen (116). However, no single technique appears to provide unequivocal results, especially in cases such as the different Mediterranean sources, and a combination is often necessary to arrive at an approximate place of origin (117). 

Mass spectral fragmentation patterns of alkyl and phenyl hydantoins have been investigated by means of labeling techniques (28—30), and similar studies have also been carried out for thiohydantoins (31,32). In all cases, breakdown of the hydantoin ring occurs by a-ftssion at C-4 with concomitant loss of carbon monoxide and an isocyanate molecule. In the case of aryl derivatives, the ease of formation of Ar—NCO is related to the electronic properties of the aryl ring substituents (33). Mass spectrometry has been used for identification of the phenylthiohydantoin derivatives formed from amino acids during peptide sequence determination by the Edman method (34). 

This tool has been of great value in the elucidation of the structures of some important biologically-derived amino (14) and deoxy (13) sugars in the form of their dialkyl dithioacetals. Tedious degradation reactions which would require both time and valuable material could be avoided in many cases by resorting to mass spectrometry. The antibiotic sugars (22) paramose (1), mycinose (2) and chalcose (3) were, for example, studied by mass spectrometry (13, 14). 

Method development is important. LC-MS performance, probably more than any other technique involving organic mass spectrometry, is dependent upon a range of experimental parameters, the relationship between which is often complex. While it is possible (but not always so) that conditions may be chosen fairly readily to allow the analysis of simple mixtures to be carried out successfully, the widely variable ionization efficiency of compounds with differing structures often makes obtaining optimum performance for the study of all components of a complex mixture difficult. In such cases, the use of experimental design should be seriously considered. 

The data in Table I are also significant in terms of the type of analysis to determine the presence of NDMA. In all cases analysis was done using gas chromatography coupled with a Thermal Energy Analyzer, a sensitive, relatively specific nitrosamine detector (12). Further, in six of the studies, the presence of NDMA in several samples was confirmed by gas chromatography-mass spectrometry (GC-MS). The mass spectral data firmly established the presence of NDMA in the beer samples. 

In order to relate material properties with plasma properties, several plasma diagnostic techniques are used. The main techniques for the characterization of silane-hydrogen deposition plasmas are optical spectroscopy, electrostatic probes, mass spectrometry, and ellipsometry [117, 286]. Optical emission spectroscopy (OES) is a noninvasive technique and has been developed for identification of Si, SiH, Si+, and species in the plasma. Active spectroscopy, such as laser induced fluorescence (LIF), also allows for the detection of radicals in the plasma. Mass spectrometry enables the study of ion and radical chemistry in the discharge, either ex situ or in situ. The Langmuir probe technique is simple and very suitable for measuring plasma characteristics in nonreactive plasmas. In case of silane plasma it can be used, but it is difficult. Ellipsometry is used to follow the deposition process in situ. 

Automated organic and elemental ion mapping of TLC plates by LMMS techniques, without focus correction, has been reported [802,839]. One of the early TLC-MS scanners used laser desorption combined with Cl detection [807,808]. The use of laser desorption mass spectrometry (LDMS), in connection with TLC separations, allows sampling of a very small area of a spot (ca. 5 im). In this way spot homogeneity can be determined (e.g. in the case of overlapping components), and also leaves the bulk of the material unaffected for further study. An important advantage... 

Guided ion beam tandem mass spectrometry has also been employed to study the reaction of Ni+ with CS2 and COS.2410 The ground state ion Ni+ undergoes endothermic reaction to form NiS+ in both cases, as well as NiCS+ and NiCO+, respectively. Threshold values for the reactions and bond dissociation energies for the products have been determined. 

Fletcher et al. [123] used a sensitive and specific gas chromatography-mass spectrometry method for the assay of primaquine in plasma and urine for studying the plasma kinetics. Preliminary studies on the effects of single and multiple oral doses were carried out. In both cases, the drug was completely removed from plasma in 24 h. The concentration of primaquine in plasma usually reached a peak 1-2 h after oral administration. The plasma elimination half-life was about 4 h. 

The sustained attractiveness of photolabeling is apparent from its prominence in studies of y-secretase, an intramembrane protease that contributes to forming amyloid-p peptides and is a major target in Alzheimer s disease [60-62]. y-Secretase is a complex of at least four different polypeptides, and is difficult to engage with high-resolution structural methods. However, in a case of this kind that involves a known target, immunodetection of proteins can often specify the target of y-secretase inhibitor photoaffinity probes such as 19, and proteomic mass spectrometry is not needed. 

Many diseases are characterized by the expression of specific proteins1 in some cases, malignant cells yield unique protein profiles when total cellular protein extracts are analyzed by proteomic methods such as two-dimensional gel electrophoresis or matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS).2 High-throughput proteomic studies may be useful to differentiate normal cells from cancer cells, to identify and define the use of biomarkers for specific cancers, and to characterize the clinical course of disease. Proteomics can also be used to isolate and characterize potential drug targets and to evaluate the efficacy of treatments. 

High-throughput proteomic methods hold great promise for the discovery of novel protein biomarkers that can be translated into practical interventions for the diagnosis, treatment, and prevention of disease. These approaches may also facilitate the development of therapeutic agents that are targeted to specific molecular alterations in diseases such as cancer. In many cases, malignant cells yield unique protein profiles when total protein extracts from such cells are analyzed by 2-D gel electrophoresis or mass spectrometry (MS) methods. Such proteomic studies have the potential to provide an important complement to the analysis of DNA and mRNA extracts from these tissues.1... 

In the following sections, the instrumental features of direct mass spectrometry based techniques (DI-MS, DE-MS and DTMS) are presented, followed by a discussion of some mass spectra of standard compounds and reference materials. Finally, a series of case studies related to the presence of resinous materials in archaeological findings and works of art are reported and discussed. 

Case Studies Direct inlet mass-spectrometry (DI-MS)... 

Case Studies Direct Exposure-Mass Spectrometry (DE-MS)... 

Case Studies Direct Temperature Resolved Mass Spectrometry (DTMS)... 

Organic Mass Spectrometry in Art and Archaeology 6.4.3 Artwork Case Studies... 

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