Mass spectrometry data collection

Although individual laboratories find it useful to compile their own reference library files, access to very large collections of mass spectra and to published data [55] is essential. A compilation of many thousands of spectra by the Aldermaston Mass Spectrometry Data Centre and the Division of Computer Research and Technology at the National Institutes of Health [56-58] has been made available commercially. The file can be searched in a number of ways using an interactive conversational mass spectral search system via a teletype and acoustic link over telephone lines. 

Figure 5.4 Negative-ion mass spectrometry data plotted as In KT3/2 versus 1,000/7 for nitrobenzene m-dinitrobenzene and sulfur hexafluoride. The magnitude was scaled to the value of the kt for SF6 at room temperature. The data for m-dinitrohenzene exhibits two states with a and P regions. Neither of these is the ground state. The curves are calculated using the measured electron affinities of SF6 and C6F15N02 and m-C6H4(N02)2. The Qan values are determined by the data to be 1.0. The responses were obtained by injecting a solution with a known amount of the three compounds into the mass spectrometer. These data were collected at higher temperatures than those in Figure 4.5.

The Eight Peak Index of Mass Spectra, pubUshed by the Mass Spectrometry Data Center of the Royal Society of Chemistry, contains a collection of over 80,(XX) spectra. 

ABSTRACT. The use of mass spectrometry to collect data on the decomposition chemistry of nitramine compounds and the relevance of the data to the processes occurring in these materials when they are used in actu propellant and explosive applications is discussed. The simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) and time-of-flight (TOF) velocity-spectra techniques and then-application to the study of energetic materials are discussed. The means by which these techniques enhance the amount of information obtained from more conventional mass spectrometric experiments is illustrated with studies on the evaluation of the use of appearance energy measurements to study the thermal decomposition of HMX and on the identiHcation of the HMX pyrolysis products and the determination of their gas formation rates. 

A comprehensive collection of spectra from a number of sources of trimethylsilyl derivatives of organic acids of biological interest was compiled by Markey et al (1972) and subsequently included in a larger reference collection (Markey et al., 1974b) and in other library files (e.g. Mass Spectrometry Data Centre Collection, The University, Nottingham, England). In addition to spectra of trimethylsilyl (TMS) derivatives are spectra of free acids, methyl esters, methyl ester-trimethylsilyl ethers (hydroxy acids), and trimethylsilyl esters-trimethylsilyl ethers-methoximes (oxo acids or oxo hydroxy acids). 

Markey, S.P., Thobhani, H.A. and Hammond, K.B. (1972), Identification of Endogenous Urinary Metabolites by Gas Chromatography - Mass Spectrometry A Collection of Mass Spectral Data, University of Colorado Medical Center, Denver, Colorado. 

JICST/JOIS. The Japan Information Center for Science and Technology (fICST) Mass Spectral Database is accessible to users in Japan through the JICST Eactual Database System (fOlS-E). The database uses the NIST/EPA/ MSCD data collection supplemented by spectra from the Mass Spectrometry Society of Japan (84). 

The mass spectrometer (ms) is a common adjunct to a chromatographic system (see Mass spectrometry). The combination of a gas chromatograph for component separation and a mass spectrometer (gc/ms) for detection and identification of the separated components is a powerful tool, particularly when the data are collected usiag an on-line data-handling system. QuaUtative information inherent ia the separation can be coupled with the identification of stmcture and relatively straightforward quantification of a mixture s components. 

Thorinm-232 is the only non-radiogenic thorium isotope of the U/Th decay series. Thorinm-232 enters the ocean by continental weathering and is mostly in the particulate form. Early measurements of Th were by alpha-spectrometry and required large volume samples ca. 1000 T). Not only did this make sample collection difficult, but the signal-to-noise ratio was often low and uncertain. With the development of a neutron activation analysis " and amass spectrometry method " the quality of the data greatly improved, and the required volume for mass spectrometry was reduced to less than a liter. Surface ocean waters typically have elevated concentrations of dissolved and particulate 17,3 7,62... 

Walker et al. [17] studied profiles of hydrocarbons in sediment according to depth in sediment cores collected at Baltimore Harbour in Chesapeake Bay, Massachusetts. Gas liquid chromatography was used to detect hydrocarbons present at different depths in the sediment, while low resolution mass spectrometry was employed to measure concentrations of paraffins, cycloparaffins, aromatics and polynuclear aromatics. Their data show that the concentrations of total and saturated hydrocarbons decreased with increased depth, and it is commented that identification and quantitation of hydrocarbons in oil-contaminated sediments is required if the fate of these compounds in dredge spoils is to be determined. 

The largest increase in experimental measurements on aqueous solutions has been in those designed to furnish information on molecular interactions and order. These techniques, along with the kinds of information which can be derived from them, are outlined in Figure 5. Although the principles behind all these techniques have been known for many years, advances in instrumentation and in data collection have encouraged their widespread application to solutions of all kinds. The use of mass spectrometry to study interactions between isolated solvent and solute molecules has been perfected largely within the past ten years. This topic is reviewed in reference (113). 

A reevaluation of molecular structure of humic substances based on data obtained primarily from nuclear magnetic resonance spectroscopy, X-ray absorption near-edge structure spectroscopy, electrospray ionization-mass spectrometry, and pyrolysis studies was presented by Sutton and Sposito (2005). The authors consider that humic substances are collections of diverse, relatively low molecular mass components forming dynamic associations stabilized by hydrophobic interactions and hydrogen bonds. These associations are capable of organizing into micellar structures in suitable aqueous environments. Humic components display contrasting molecular motional behavior and may be spatially segregated on a scale of nanometers. Within this new structural context, these components comprise any molecules... 

Fig. 5.3. Odor changes that track floral color changes. Gas chromatography-mass spectrometry total ion chromatograms of floral headspace collected from young (upper trace) and old (lower trace) flowers of Lantana montevidense. Peaks 1,8,10, and 12 are metabolites of linalool (peak 3), all of which decrease dramatically with floral age and color change. Sesquiterpene hydrocarbons (peaks 4, 5, 9, and 11) show comparable decreases over time. Peaks 2, 6, 7, 13, and 14 are oxygenated aromatics and are present only in newly opened, rewarding flowers. Insert mass spectra highlight loss of phenylacetaldehyde ( peak 7) taken from young (a) and old (b) flowers. (M. R. Weiss and R. A. Raguso, unpublished data.)...

In general more independent physical constants that are sensitive to structure are needed when it is necessary to know more structural elements of a mixture. It will be clear that, dependent on the collected basic data, statistical methods for the analysis of mixtures in general only give a certain approach to their structures, but should never be considered as the ultimate purpose. Improvement of existing methods is imperative when new and more accurate data become available the development of various physical separation methods (distillation, chromatography, thermodiffusion, etc.) and of independent physical identification methods (ultraviolet and infrared spectra, mass spectrometry) may also contribute considerably to their perfection. 

King, R. C., Gundersdorf, R., and Femandez-Metzler, C. L. (2003). Collection of selected reaction monitoring and full scan data on a time scale suitable for target compound quantitative analysis by liquid chromatography/tandem mass spectrometry. Rapid Commun. Mass Spectrom. 17 2413-2422. 

Koers, J. M. (2008). Selected ion monitoring (SIM) mode data collection using the laser diode thermal desorption (LDTD) source to increase sensitivity. In Proceedings of the 56th ASMS Conference on Mass Spectrometry and Allied Topics. ASMS, Denver, CO. 

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