Mass spectrometric measurement

Many artificial (likely radioactive) isotopes can be created through nuclear reactions. Radioactive isotopes of iodine are used in medicine, while isotopes of plutonium are used in making atomic bombs. In many analytical applications, the ratio of occurrence of the isotopes is important. For example, it may be important to know the exact ratio of the abundances (relative amounts) of the isotopes 1, 2, and 3 in hydrogen. Such knowledge can be obtained through a mass spectrometric measurement of the isotope abundance ratio. 

MS", application of successive mass spectrometric measurements n of them), particularly in linked scanning of m/z, which is the ratio of the mass (m) of an ion and the number of charges (z) on it. Older publications used m/e, but as e is the actual charge on an electron and not the number of charges on the ion, the use of m/e was abandoned, m/z. mass-to-charge ratio, a measure of molecular mass PDB. PeeDee Belemnite (a carbon isotope standard see VPDB)... 

These results, which pertain to stable-ion conditions, provide strong evidence that foe most stable structure for foe norbomyl cation is foe symmetrically bridged nonclassical ion. How much stabilization does foe a bridging provide An estimate based on molecular mechanics calculations and a foermodynamic cycle suggests a stabilization of about 6 1 kcal/mol. An experimental value based on mass-spectrometric measurements is 11 kcal/mol. Gas-phase Itydride affinity and chloride affinity data also show foe norbomyl cation to be especially stable. ... 

For comparison, Battles et al. (15) determined the partial heats of sublimation of Pu02(g) and Pu0(g) above PuOi.33 over the temperature range 1937 to 2342 K by means of mass spectrometric measurements with Iridium effusion cells. The absence of Iridium oxides or Iridium species In the vapor phase Indicated that Iridium was nonreducing toward plutonia. The partial heats of sublimation calculated from the slopes of the temperature dependency data yielded values of 127.1 1.2 and 138.8 1.6 kcal/mol for Pu0(g) and Pu02(g) ... 

Most information concerning ion-molecule reactions in flames has been obtained from mass spectrometric measurements, but some inferences have been drawn from results of other types of experiments... 

This work was supported by Contract No. NOl-CO-75380 with the National Cancer Institute, NIH, Bethesda, Maryland 20205. The authors are particularly grateful to Dr. P.N. Magee and Ms. Cecilia Chu for their stimulating collaboration, to Drs. R. Smith and R. Kupper, our former colleagues, who made substantial contributions to this research, and to Dr. G. McClusky for carrying out the difficult mass spectrometric measurements. 

In a recently pnblished example of betaxanthin analyses in a complex food matrix, 19 betaxanthins were assigned in yellow Swiss chard petioles. Mass spectrometric measnrements are even more helpfnl if nnknown betacyanin structures are to be elucidated. While betacyanic plant materials such as red beet and amaranth may still be commercially available for coinjection experiments and comparison with samples under investigation, it may be an easier task to first optimize pigment separation followed by mass spectrometric measurements. 

Chabaux F, Ben Othman D, Birck J-L (1994) A new Ra-Ba chromatographic separation and its application to Ra mass-spectrometric measurements in volcanic rocks. ChemGeol 114 191-197 Cheng H, Edwards RL, Hoff J, Gallup CD, Richards DA, Asmerom Y (2000) The half hves of uranium-234 and thorium-230. ChemGeol 169 17-33... 

Resonance ionization methods (RIMS) have also been explored for improving Th ionization efficiency for mass spectrometric measurement (Johnson and Fearey 1993). As shown in Figure 3, two lasers are required, a continuous resonant dye laser for resonance of thorium atoms, and a continuous UV argon laser for transition from resonance to ionization. Consequently, sophisticated laser instrumentation is required for these methods. 

Williams RW, Collerson KD, Gill JB, Deniel C (1992) High Th/U ratios in subcontinental lithospheric mantle mass spectrometric measurement of Th isotopes in Gaussberg lamproites. Eartli Planet Sci Lett 111 257-268... 

Mass spectrometric measurements on corals typically result in errors in and °Th of 2 per mil or better (2a), with the exception that fractional error in °Th typically increases progressively from this value for samples progressively younger than several ka. This results from the low concentrations of °Th in very young corals. Errors in Pa are typically somewhat larger than those of the other isotopes, with errors of several per mil, except for corals younger than a few ka. 

Chabaux F, Ben Othman D, Birck JL (1994) A new Ra-Ba chromatographic separation and its application to Ra mass-spectrometric measurement involcanics rocks. Chem Geol 114 191-197... 

Soon after this discovery the harnessing of the technique to the measurement of all the U isotopes and all the Th isotopes with great precision immediately opened up the entire field of uranium and thorium decay chain studies. This area of study was formerly the poaching ground for radioactive measurements alone but now became part of the wonderful world of mass spectrometric measurements. (The same transformation took place for radiocarbon from the various radioactive counting schemes to accelerator mass spectrometry.)... 

Fig. 4.23. Distribution of concentration of oxygen in upper atmosphere / -obtained with a semiconductor sensor on December 27, 1979 near observation site Volgograd (present investigation) 2, 3 the data of mass-spectrometric measurements 4, 5 - the data of a resonance spectroscopy 6 — silver films 7, 8 - model calculations...

Table 7.83 lists the main characteristics of TLC-FAB-MS/LSIMS. A key difference between EI/CI and FAB/LSIMS/LD is the fact that sampling in FAB and LSIMS is from a specified location that corresponds to the impact footprint of the primary particle beam. The natural compatibility of FAB, LSIMS and LD with the direct mass-spectrometric analysis of TLC plates is readily apparent. Most mass-spectrometric measurements are destructive in nature, but FAB and LSIMS are surface-sensitive techniques in which the material actually consumed in the analysis is sputtered only from the top few microns of the sample spot. The underlying bulk is not affected, and can be used for further probing. The major limitation of TLC-FAB depends on the capability of the compounds to produce a good spectrum. 

The Heat of Formation of CF2. Several of experimental approaches have been used to determine AHf° (CF2).The most common technique involves mass spectrometric measurement of appearance potentials. The earlier appearance potential measurements indicated that A(CF2) = -30 10 kcal. mole 32), but it now appears this value is too high. Margrave and co-workers 33 reported a mass spectrometric study of the C2F4/CF2 equilibrium between 1127—1244 °K. Both second and third-law determinations of the enthalpy of reaction for C2F4 - 2 CF2 were made, yielding-39.3 3 kcal. mole 1 for A/fy-°298 (CF2, g). 

Mass spectrometric measurements of ions desorbed/ionized from a surface by a laser beam was first performed in 1963 by Honig and Woolston [151], who utilized a pulsed mby laser with 50 p,s pulse length. Hillenkamp et al. used microscope optics to focus the laser beam diameter to 0.5 p,m [152], allowing for surface analysis with high spatial resolution. In 1978 Posthumus et al. [153] demonstrated that laser desorption /ionization (LDI, also commonly referred to as laser ionization or laser ablation) could produce spectra of nonvolatile compounds with mass > 1 kDa. For a detailed review of the early development of LDI, see Reference 154. There is no principal difference between an LDI source and a MALDI source, which is described in detail in Section 2.1.22 In LDI no particular sample preparation is required (contrary to... 

Isotopic fractionation provides illustrative examples of first-order expansions of unknown functions. In general, the mass spectrometric measurement r/ of the ratio between two isotopes of mass m( and m, of the same element, differs from the natural value R/. Only a very small fraction of the original sample produces ions and different processes taking place in different parts of the mass spectrometer act differently on the sensitivity of each isotope. We assume that instrumental isotopic fractionation is mass-dependent. 

The slight shift results from the differences in dissociation in such measurements. This could be proved by simultaneous mass spectrometric measurement which showed the presence of various vaporized species. 

Mass spectrometric measurements coupled with solution thermochemical results are the sources of solvation enthalpy values for anions and cations. These data are related to the lattice energy, which is a parameter used to assess the ionic character of solids and predict their standard enthalpies of formation. An introduction to that... 

It should, however, be mentioned that Mulliken s study of the BO system has been followed over the years by many others, An extensive study by Jenkins and McKellar (1932) should be mentioned explicitly. This study involved the long wavelength band of BO. The same method as that used by both Jevons and Mulliken to produce the BO was used in this work. The new (present day) quantum mechanics was used in the theoretical interpretation. Both the vibrational and the rotational isotope effects were observed and agree with theory. One motivation for this work was to determine how well the isotopic ratio of the square roots of the two relevant isotopic masses (10B and nB) agrees with the ratio obtained from Aston s mass spectrometric measurements and hence how well isotopic mass ratios determined from band spectra compare with those obtained using Aston s mass spectrograph. 

Matrix-assisted laser desorption ionization mass spectrometry (MALDI) uses a matrix, typically of aromatic acids, whose molecular weight is similar to those of typical metabolites and thus disallows the mass spectrometric measurement of the latter. 

Franklin et al. 1986). None of these techniques has enjoyed long term success. Measurement of Li isotopes by mass spectrometry faces the primary problem of controlling mass fractionation from the emitter. Ironically, the very property that makes Li geochemically interesting makes quantifying its isotopic composition with precision extraordinarily challenging. For this reason, mass spectrometric measurements of Li must be compared directly to a standard material. As long as all laboratories make use of the same standard material, its isotopic composition is academic, as the measured isotopic composition of the standard drops out of the arithmetic of normalization. 

Huang SM, Strangman NM, Walker JM. 1999. Liquid chromatographic-mass spectrometric measurement of the endogenous cannabinoid 2-arachidonylglcerol in the spinal cord and peripheral nervous system. Zhongguo Yao Li Xue Bao 20 1098. 

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