Mass Spectrometric Analysers

In a mass spectrometer ion formation, mass analysis, and ion detection are combined. Various mass analysers have been developed to separate ions according to their mass-to-charge ratio. Each analyser has its own special characteristics and field of application. No mass analyser can match all possible requirements. The choice of the analyser should generally be based upon the application, the performance desired, and cost. 

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The most stable protected alcohol derivatives are the methyl ethers. These are often employed in carbohydrate chemistry and can be made with dimethyl sulfate in the presence of aqueous sodium or barium hydroxides in DMF or DMSO. Simple ethers may be cleaved by treatment with BCI3 or BBr, but generally methyl ethers are too stable to be used for routine protection of alcohols. They are more useful as volatile derivatives in gas-chromatographic and mass-spectrometric analyses. So the most labile (trimethylsilyl ether) and the most stable (methyl ether) alcohol derivatives are useful in analysis, but in synthesis they can be used only in exceptional cases. In synthesis, easily accessible intermediates of medium stability are most helpful. 

Amides are derivatives of carboxylic acids, so that their coordination behavior to boranes might be similar to that of their parent compounds. B-NMR spectroscopic studies have shown that compounds 31 and 32 are monomeric species in solution, while compounds 33 and 34 with the more Lewis acidic 9-borabicyclo[3.3.1]nonyl unit form aggregates that may be dimeric, oligomeric, or polymeric. The grade of association could not be determined by mass spectrometric analyses, because in all cases only the monomer is liberated into the gas phase [65]. 

Herbach, K.M., Stintzing, E.C., and Carle, R., Thermal degradation of betacyanins in juices from purple pitaya (Hylocereus polyrhizus [Weber] Britton Rose) monitored by high-performance liquid-chromatography-tandem mass spectrometric analyses, Fur. Food Res. TechnoL, 219, 377, 2004. 

Many of the aforementioned techniques are not appropriate to direct mass-spectrometric analyses of intact high-MW and heat-labile compounds. For such samples, thermal degradation techniques (analytical pyrolysis) can be performed to generate more-volatile compounds of lower molecular weight that are amenable... 

Results of pyrolysis mass spectrometric analyses can be influenced by both phenotypic drift and instrument drift. Phenotypic drift can result from variations in culture growth immediately prior to analysis, and from variations during serial subculturing before analysis.125,126 However, this type of drift is not perceived as an obstacle in microbiological work because it can be largely overcome by standardizing culture conditions and by analyzing more than one sample from each culture. 

Everson J, Patterson CC. 1980. "Ultra-clean" isotope dilution/mass spectrometric analyses for lead in human blood plasma indicate that most reported values are artificially high. Clin Chem 26 1603-1607. 

C. Hecht, S. Bieler, C. Griehl, Liquid chromatographic mass spectrometric analyses of anae rohe protein degradation products, Journal of Chromatography A, 1088, 121 125 (2005). 

The electron ionization (El) mass spectra of TMS ethers and esters are generally characterised by weak or absent molecular ions. The [M—15]+ ion formed by loss of a methyl radical is generally abundant and in the case of alcoholic functions, the loss of a trimethylsilanol molecule [M—90]+ is also diagnostic. The peak at mJz 73, corresponding to the TMS group, is important in nearly all the TMS-derivative mass spectra. Figure 8.2 shows the fragmentation of TMS esters and ethers in mass spectrometric analyses. 

Figure 8.2 Fragmentation of trimethysilyl esters (a) and ethers (b) in mass spectrometric analyses...

Mass spectrometers have been used at some level in all of these types of investigations because of their unsurpassed sensitivity and specificity, their multicomponent analytical capability and, in some cases, their ability to provide precise and accurate isotope ratios. Traditional methods of analysis typically involve the collection of water and sediment samples, or biological specimens, during field expeditions and cmises on research vessels (R/Vs), and subsequent delivery of samples to a shore-based laboratory for mass spectrometric analyses. The recent development of field-portable mass spectrometers, however, has greatly facilitated prompt shipboard analyses. Further adaptation of portable mass spectrometer technology has also led to construction of submersible instruments that can be deployed at depth for in situ measurements. 

Harless RL, Harris DE, Sovocool GW, et al. 1978. Mass spectrometric analyses and characterization of Kepone in environmental and human samples. Biomed Mass Spectrom 5(3) 232-237. 

Carr, R.H. Jackson, A.T. PreUminary MALDI-TOF and Field Desorption Mass Spectrometric Analyses of Polymeric Methylene Diphenylene Diisocyanate, Its Amine Precursor and a Model Polyedier Prepolymer. Rapid Commun. Mass Spectrom. 1998, 72,2047-2050. 

Tables have been produced that indicate the most common molecular masses found for amino acid residues in mass spectrometric analyses.

Zhang, H. Zhang, D. Ray, K. A software filter to remove interference ions from drug metabolites in accurate mass liquid chromatography/ mass spectrometric analyses. J. Mass Spectrom. 2003, 38, 1110-1112. 

M. A. Strege High-performance liquid chromatographic-electrospray ionization mass spectrometric analyses for the integration of natural products with modem high-... 

Electrospray (ESI) is an atmospheric pressure ionization source in which the sample is ionized at an ambient pressure and then transferred into the MS. It was first developed by John Fenn in the late 1980s [1] and rapidly became one of the most widely used ionization techniques in mass spectrometry due to its high sensitivity and versatility. It is a soft ionization technique for analytes present in solution therefore, it can easily be coupled with separation methods such as LC and capillary electrophoresis (CE). The development of ESI has a wide field of applications, from small polar molecules to high molecular weight compounds such as protein and nucleotides. In 2002, the Nobel Prize was awarded to John Fenn following his studies on electrospray, for the development of soft desorption ionization methods for mass spectrometric analyses of biological macromolecules. ... 

The purpose for the 1998 study was to assess the ability of and determine the means whereby member facilities identify and solve problems in peptide synthesis 10 The potential for oxidation of amino acids such as methionine is always a concern for peptide chemists and biomedical researchers. A peptide mixture containing 70% correct peptide and 30% oxidized peptide was prepared and sent to member facilities to determine if the oxidized methionine would be detected (see Table 1). In addition to the oxidized peptide, a reverse synthesized peptide was sent to the participants. In previous studies, peptides had been submitted which had been synthesized in the reverse order and if only HPLC and mass spectrometric analyses was performed, the reverse synthesis would not be identified. Therefore, two peptides were designed with the second in the reverse order with two substitutions to equal the mass of the first peptide. These two peptides were readily separated by HPLC. The second peptide was sent to the laboratories, but the laboratories were given the first sequence and asked if the correct peptide had been made. Out of 20 participating laboratories ... 

Note that, during mass spectrometric analyses, the isotopic composition (230rh/232-ph) is measured independently from (2 U/2 2 ph) and thus the errors of these two ratios are not correlated, even though they have the same denominator in 2 h. (22 U/22 Th) is obtained by isotope dilution method while (2 h/2 2jjj is measured directly by mass spectrometers. 

Mass spectrometric studies were carried out as a first qualitative means of checking for dicarboxylate anion binding (see also Section 3). Here, mixtures of sapphyrin dimer 15 and several representative dicarboxylate anions, such as oxalate, 4-nitrophthalate, 5-nitroisophthalate and nitroterephthalate in methanol, were subjected to high resolution FAB mass spectrometric (HR FAB MS) analysis using FAB positive NBA matrix. In general, peaks for the putative complexes were seen, lending credence to the hypothesis that the dicarboxylate substrates in question were, in fact, being bound by 15 under the matrix desorption/gas phase conditions used to effect these mass spectrometric analyses. 

P. Rochlin, "Mass Spectrometric Analyses of Gaseous Combustion Products from Delay Powders (Research and Development of Delay Powders for Ammunition Fuze Application-General) , -PATR 2006 (March 1954)... 

This chapter concerns the fields that use inorganic mass spectrometry to investigate the composition and evolution of matter in the universe and in the solar system. Cosmochemistry is related to nuclear astrophysics, because almost all the chemical elements were synthesized by nuclear reactions in the interior of stars.1 Mass spectrometric analyses of elemental composition, the distribution and variation of isotope abundances are very helpful, especially for cosmochronological studies, in order to explain the formation, history and evolution of stars in our universe and to understand the chemical and nuclear processes. 

Figure 6 shows chromatograms from reverse-phase HPLC separations of the extracts of chlorinated tyrosine and chlorinated phenylalanine. Authentic standards were used to locate the compounds that had previously been identified by GC-MS. The chromatograms show the presence of several compounds not observed by GC-MS. This result indicates the presence of products of chlorination, which are nonvolatile. Other techniques are currently being employed to identify such compounds, for example, HPLC fractionation techniques combined with mutagenicity testing of the fractions and soft-ionization mass spectrometric analyses of the mutagenic fractions. 

A 20% polyethylene glycol succinate on Kieselguhr column (1.2 m, 443 K, 50 ml min helium carrier gas) was used for GC analyses. Deuterium-labelled compounds were analysed by NMR spectroscopy (JEOL C 60-HL equipment) after separation with a Carlo Erba Mod P preparative GC. Mass spectrometric analyses of the reaction mixtures were carried out with a Hewlett Packard 5890A GC instrument (25 m HP-20M column, 353-473 K) coupled with a 5970 MSD quadrupole mass spectrometer (El source, 70 eV, 1-s scans, HP 59970 MS ChemStation data system). 

The simulated distillation data (Table V and Figures 2, 4, 6) and the FIA analyses of the distillates (Table II) were obtained by standard ASTM methods D2887 and D1319, respectively. The mass spectrometric analyses (MS) of the saturates fractions (Table VI) were obtained by an in-house method similar to that of Hood and O Neal (44). The aromatic fractions were analyzed by the proton nuclear magnetic resonance (NMR) method of Clutter et al. (45), and the results are reported in Tables VII and VIII. 

The mass spectrometric analyses of the saturate fractions are reported in Table VI. These fractions appear to be composed mostly of alkanes and noncondensed cycloalkanes with smaller amounts of condensed cycloalkanes, mainly two- and three-ring systems. However, because of the presence of olefins in these fractions the analyses are only semiquantitative. In fact, an olefin should make a contribution to the cycloalkane group type which has the same molecular weight. That is, a monoolefin will contribute to the cycloalkanes, a diolefin or a cyclic olein will contribute to the bicycloalkanes, etc. However, to determine the extent of these contributions more analytical work is necessary. 

FAB mass spectrometric analyses require a high-energy atom beam, usually 6-10 keV. The atom beam, typically xenon, is directed at the sample which is dissolved in a matrix. Typical matrices include glycerol, thioglycerol, m-mtrobcnzyl alcohol and a mixture of dithiothreitol and dithioerythritol. The continual bombardment of the sample/matrix mixture results in desorption of both species. Ions are formed, either as pre-formed ions from the matrix or in the gas phase immediately above the sample surface. 

The skillful technical assistance of Miss Christine Stroh-meier and Ingo Keller is gratefully acknowledged. Hermann Moll is thanked for mass spectrometric analyses. 

We acknowledge the assistance of Nikhil S. Dodhiwala who performed most of the SFE work, of Janet Benedicto and Lisa Balch, who performed all gas chromatographic and gas chromatographic/mass spectrometric analyses reported in this manuscript, and of Karin Bauer of Midwest Research Institute, who provided input on the statistical analysis of the preliminary results from our method optimization study. We would also like to acknowledge the assistance of Ashok Shah and Carl Stadler of Suprex Corporation who helped with the design of the dual-extraction setup on the Suprex SE-50 system, and of Hewlett-Packard Company who made available to us a Hewlett Packard extractor. 

Mass spectrometric analyses were provided by Mr. Lawrence R. Phillips and Ms. Betty Baltzer of the Michigan State University - NIH Mass Spectrometry Facility, and are sincerely appreciated. 

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