Spectroscopic isotope ratios

The usual procedure for radiocarbon dating is to bum a tiny sample of the object to be dated, collect the CO2 that is produced, and compare its rate of radioactive decay with that of a fresh CO2 sample. The ratio of counts gives Nq jN, which can then be substituted into Equation to calculate t. Mass spectroscopic isotope analysis can also be used to obtain the Nq jN value, as Example illustrates. 

Mass spectroscopic studies of organometallic compounds are almost as old as the field of mass spectrometry nickel tetracarbonyl was studied by J. J. Thomson (/) and Aston (2,3) in their work on the isotope ratios of nickel. Following this early flurry of specialized interest, however, inorganic and organometallic mass spectral studies were... 

In addition to sensory and physical properties, the content of certain typical components is determined. Problems concerning the natural, botanical, and geographical origins of these products are also solved by using modern chromatographic methods such as enantiomer separations [843-843c], and spectroscopic analytical techniques such as isotope ratio mass spectrometry (IRMS) [844-844b],... 

Spectroscopic interferences. These can alfect the ion intensity of an isotope and, therefore, the isotope ratio measurement. One would try to minimise such interferences by resorting to any of the techniques and technologies, and also the mathematical correction strategies, described in the previous section. 

The parameters in the effective Hamiltonian iCrjV may not all be determinable from spectroscopic data. When indeterminacies occur, they can often be resolved by utilising data from different isotopic forms. The parameters Xnv and Xnov in the equations above do not themselves have simple isotopic ratios but the coefficients of the powers of (o + 1 /2) in the expansions (7.168) and (7.182) do. The isotopic ratios for Xe, X e, X J,..., are the same as for X(R) itself and the ratio Be/o>e is proportional to ji 1/2. Thus the isotopic ratio for any of the coefficients in Xnv and XrtDv is readily determined. 

In 2005, De Laeter discussed the role of isotope reference materials for the analysis of non-traditionaT stable isotopes. At present, no isotopically certified reference materials exist for a large number of elements, including Cu, Zn, Mo and Cd, and it is important that this situation be rectified as soon as practicable. Before the isotopically certified reference materials become available for selected elements, suitable reference materials can be created as a standard if sufficient and reliable isotope data have been obtained by interlaboratory comparisons. For example, the Hf/ Hf isotope ratio was measured using hafnium oxide from Johnson Matthey Chemicals, JMC-475, for hafnium isotope ratio measurements with different multi-collector mass spectrometers (ICP-MS and TIMS) as summarized in Table 8.1. However, no isotope SRM is certified for the element Mo either. Mo isotope analysis is relevant, for example, for studying the isotope fractionation of molybdenum during chemical processes or the isotope variation of molybdenum in nature as the result of the predicted double (3 decay of Zr or 18.26-28 spectroscopically pure sample from Johnson Mattey Specpure is proposed as a laboratory standard reference material if sufficient and reliable isotope data are collected via an interlaboratory comparison. 

For an exact characterization of the investigated systems, besides the isotope ratio measurement, one has to carry out the quantitative analysis of polyethers, and of the corresponding metal complexes as well. The analysis method which is most commonly described in the literature for polyethers is NMR spectrometry However, this spectroscopic method is not very precise for a quantitative determination. Therefore, other types of analysis have been developed, e.g. a gravimetric procedure and a titrimetric method using the standard addition technique with a potentiometric indication... 

Applications of ICP-MS cover a wide range of sample types which often make use of its excellent sensitivity and isotope ratio capabilities, such as the determination of ultra-low levels of impurities in semiconductors, long-lived radionuclides in the environment, and geochronology. ICP-MS is well suited to the determination of the lanthanide series of elements in many geological applications. Sample preparation methods are similar to those generally used for trace metals analysis however, nitric acid is favored for sample digestion because other mineral acids contain elements which cause spectroscopic in-teferences. 

The principle technique used for the measurement of isotope ratios is mass spectrometry (MS) using various combinations of ion source and mass analyzer for the analysis of many organic and inorganic materials. Less frequently employed are spectroscopic techniques such as optical absorption and emission, and nuclear magnetic resonance (NMR). 

Although spectroscopic methods are far less precise than IRMS for isotope ratio measurements, they can have advantages in terms of costs and ease of operation. These techniques also remove the laborious chemical preparation required for conventional IRMS. They are most commonly applied to the analysis of samples that are artificially enriched in the heavier isotopes of nitrogen, carbon, and oxygen. 

MS provides a powerful capability for in situ exploration of planetary environments. MS can be used to identify the abundances of atomic and molecular species, determine isotopic ratios, and thereby answer many of the fundamental questions regarding the creation and evolutions of the solar system. Here we discuss briefly some of the results from mass spectroscopic instruments on previous and on-going space missions as listed chronologically in Table 17.1. 

Spectroscopic techniques used in essential oil analysis comprise ultraviolet and visible spectrophotometry, infrared spectrophotometry (IR), mass spectrometry (MS), and nuclear magnetic resonance spectroscopy (NMR), including the following H-NMR, C-NMR, and site-specific natural isotope fractionation NMR. Combined techniques (hyphenated techniques) employed in essential oil analysis are GC/MS, liquid chromatography/mass spectrometry, gas chromatography/Fourier transform infrared spectrophotometry (GC/FT-IR), GC/FT-IR/MS, GC/atomic emission detector, GC/isotope ratio mass spectrometry, multidimensional GC/MS. 

The method of standard additions efficiently compensates for matrix effects but not for drift. If the latter is also present (for instance because of gradual clogging), internal standardization may also be required. The best method to compensate for both matrix effects and drift is isotope dilution analysis. However, it is only applicable to elements with at least two isotopes (stable and/or long-lived radioactive) free of spectroscopic interferences. Because of mass discrimination, this normally standardless technique requires a prior determination of mass bias using standards of known isotopic composition in order to correct the measured isotope ratios for mass discrimination. 

A main obstacle in accurate isotope ratio determination using MC-ICP-MS is correction for instrumental mass bias, which becomes particularly important because of the excellent precision achieved on isotope ratios achieved with this technique. The mass bias observed is usually in the percent range (per amu), and can drift over time. This may be due to spectroscopic interference effects, or matrix-derived differences in the mass bias produced during the measurement of a sample compared to the measurement of the isotopic standard used for mass bias correction. ... 

Mass-spectroscopic technique has also been used with non-fissile targets after pile or cyclotron bombardment to determine the mass-numbers of radioactive nuclides. In one case, the branching ratios of certain isotopes for and electron capture decay (where different elements are produced by the two routes) were determined from the amount of the stable end-products of radioactive decay, using the mass-spectrometer to identify the isotopes concerned and to correct for any stable impurities of the elements concerned (98). For some purposes, mass-spectroscopic separations could be very valuable technically such as the... 

The vibrational frequencies of isotopic isotopomers obey certain combining rules (such as the Teller-Redlich product rule which states that the ratio of the products of the frequencies of two isotopic isotopomers depends only on molecular geometry and atomic masses). As a consequence not all of the 2(3N — 6) normal mode frequencies in a given isotopomer pair provide independent information. Even for a simple case like water with only three frequencies and four force constants, it is better to know the frequencies for three or more isotopic isotopomers in order to deduce values of the harmonic force constants. One of the difficulties is that the exact normal mode (harmonic) frequencies need to be determined from spectroscopic information and this process involves some uncertainty. Thus, in the end, there is no isotope independent force field that leads to perfect agreement with experimental results. One looks for a best fit of all the data. At the end of this chapter reference will be made to the extensive literature on the use of vibrational isotope effects to deduce isotope independent harmonic force constants from spectroscopic measurements. 

Cl is sufficiently common that some vibrational frequencies of isotopically heavy methyl chloride have been measured spectroscopically, so it is possible to compare measured and model frequency shifts. It is found that V3 and V6 are the only frequencies that shift signiftcantly when Cl is substituted for Cl the model estimates that the ratio of V3 in C H3 C1 divided by the frequency in is 0.9919, for the ratio is 0.9996. These... 

The theory developed for perfect gases could be extended to solids, if the partition functions of crystals could be expressed in terms of a set of vibrational frequencies that correspond to its various fundamental modes of vibration (O Neil 1986). By estimating thermodynamic properties from elastic, structural, and spectroscopic data, Kieffer (1982) and subsequently Clayton and Kieffer (1991) calculated oxygen isotope partition function ratios and from these calculations derived a set of fractionation factors for silicate minerals. The calculations have no inherent temperature limitations and can be applied to any phase for which adequate spectroscopic and mechanical data are available. They are, however, limited in accuracy as a consequence of the approximations needed to carry out the calculations and the limited accuracy of the spectroscopic data. 

Theoretical studies by Polyakov (1997), Polyakov et al. (2007) and Schauble et al. (2001) predicted Fe isotope fractionations of several %c between various iron oxides, carbonates and sulfides from spectroscopic data, even at high temperatures. Fe/ " Fe ratios will be usually higher in Fe + compounds than in Fe + bearing species. First experimental studies at magmatic temperatures were conducted by SchiiBler et al. (2007) for equilibrium isotope fractionations between iron sulfide... 

The intrinsic variable expressed as units of radioactivity (in becquerels or, more traditionally, curies) per mole of a substance. One Bq corresponds to 1 disintegration per second (dps) and one Ci to 3.70 x 10 ° Bq. This parameter is especially useful in quantifying the amount of substance in biological samples. For example, if SAs is the standard specific radioactivity (say, x dps/y mol) of a standard, and if SAg is the experimental specific activity (say, x dps/(y + z) mol), then the content z in a sample can be determined from the expression (SAs/ SAe) = (y + z)/y or z = y ([SAj/SAg] - 1). This intrinsic variable can also be expressed as the gram-atom excess of a stable isotope per mole of a substance. The numerator is typically determined using a ratio mass spectrometer, and the denominator can be estimated by chemical and/or spectroscopic techniques. 

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