Spectrometric measurements

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) ... 

Spectrometric measurements, mass, with irridium effusion cells, heats... 

Solutions with low content of alcohol and alcohol ether sulfates cannot be analyzed by the two-phase method and specialized procedures have been developed. ISO method 7875/1 [267] is the standard method for analyzing sulfates and other anionic surfactants at very low concentrations, such as in waste-waters. The absorbance of the chloroform layer containing the surfactant-dye complex is spectrometrically measured at 650 nm and quantified using a calibration curve. Different improvements of this method have been developed [268,269]. 

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... 

In addition to instrumental improvements, various approaches have been used to improve the purity or geometry of sources of natural samples for gamma spectrometric measurement. For example, improvements in source preparation for " Th measurement in water and sediment samples by gamma spectrometry are discussed in Cochran and Masque (2003). It should be emphasized that one of the main advantages of gamma spectrometry is ease of use, since in many cases samples may be analyzed directly or with significantly reduced sample preparation compared to alpha, beta, or mass spectrometric techniques. 

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... 

In 1988, Chen and Yuan published U-series dates on bones and teeth for more than 20 Chinese sites, providing the first extensive Palaeolithic chronology for China. They used a-spectrometric measurements of °Th/U, and and used concordance... 

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. 

Prange et al. [809,810] carried out multielement determinations of the stated dissolved heavy metals in Baltic seawater by total reflection X-ray fluorescence (TXRF) spectrometry. The metals were separated by chelation adsorption of the metal complexes on lipophilised silica-gel carrier and subsequent elution of the chelates by a chloroform/methanol mixture. Trace element loss or contamination could be controlled because of the relatively simple sample preparation. Aliquots of the eluate were then dispersed in highly polished quartz sample carriers and evaporated to thin films for spectrometric measurements. Recoveries (see Table 5.10), detection limits, and reproducibilities of the method for several metals were satisfactory. 

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). 

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