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Single isotope ratios measurement

Secondary isotope effects are small. In fact, most of the secondary deuterium KIEs that have been reported are less than 20% and many of them are only a few per cent. In spite of the small size, the same techniques that are used for other kinetic measurements are usually satisfactory for measuring these KIEs. Both competitive methods where both isotopic compounds are present in the same reaction mixture (Westaway and Ali, 1979) and absolute rate measurements, i.e. the separate determination of the rate constant for the single isotopic species (Fang and Westaway, 1991), are employed (Parkin, 1991). Most competitive methods (Melander and Saunders, 1980e) utilize isotope ratio measurements based on mass spectrometry (Shine et al., 1984) or radioactivity measurements by liquid scintillation (Ando et al., 1984 Axelsson et al., 1991). However, some special methods, which are particularly useful for the accurate determination of secondary KIEs, have been developed. These newer methods, which are based on polarimetry, nmr spectroscopy, chromatographic isotopic separation and liquid scintillation, respectively, are described in this section. The accurate measurement of small heavy-atom KIEs is discussed in a recent review by Paneth (1992). [Pg.234]

Instrumental developments (e.g., of sector field instruments with multiple ion collection, introduced in 1992, or the insertion of collision and reaction cells in order to reduce disturbing isobaric interferences), the progress in applications for ultratrace analysis, also in combination with on line hyphenated separation techniques (HPLC, CE), especially routine capability as well as decreasing price and user friendly maintenance mean that sales are increasing by 10 % every year. To improve the analytical performance of ICP mass spectrometers for precise isotope ratio measurements (e.g., for geochronology or for the study of fine isotope variation in nature) powerful instrumentation with high mass dispersion and multiple ion collector systems instead of single ion collection are commercially available on the analytical market. [Pg.120]

Of all the different mass spectrometric techniques for isotope analysis (such as ICP-MS, LA-ICP-MS, TIMS, GDMS, AMS, SIMS, RIMS and isotope ratio mass spectrometry of gases), the greatest proportion of pubhshed papers today concern ICP-MS with single and multiple ion collection.19 Due to its benefits, ICP-MS has now become a widely accepted method for isotope analysis and allows isotope ratios to be measured in a short time with good accuracy and precision.9,19,75 78 As discussed above, as a powerful and universal tool, ICP-MS has opened up new applications for isotope ratio measurements of elements with a high first ionization potential, which are difficult to analyze with TIMS (such as Mo, Hf, Fe). Of all the heavy metals studied, uranium was favoured by ICP-MS and LA-ICP-MS. [Pg.228]

The results of uranium isotope ratio measurements by MC-TIMS (TRITON Thermo Fisher Scientific) on a single uranium oxide reference particle (10 pan) are illustrated in Figure 8.5.9,144 The high precision of multiple ion counters and high detection power in the MC-TIMS are... [Pg.237]

The significance of inorganic mass spectrometry in precise isotope ratio measurements will be further increased for sector field mass spectrometers with multiple ion collector systems and also for mass spectrometers with single ion detection or quadrupole based instruments with and without a collision cell. [Pg.461]

Figure 16.24—Instrument for isotope ratio measurements. The high sensitivity required by these types of analyses is achieved by placing several Faraday-type detectors after the magnet, each recording the current at a single mass. A reference standard is injected with the sample. Figure 16.24—Instrument for isotope ratio measurements. The high sensitivity required by these types of analyses is achieved by placing several Faraday-type detectors after the magnet, each recording the current at a single mass. A reference standard is injected with the sample.
Since the introduction of the first commercial instrument in 1983, inductively coupled plasma mass spectrometry (ICP-MS) has become widely accepted as a powerful technique for elemental analysis. Two excellent books on ICP-MS have been published [1,2]. ICP-MS provides rapid, multielement analysis with detection limits at single parts part trillion or below for about 40 to 60 elements in solution and a dynamic range of 104 to 108. These are the main reasons most ICP-MS instruments have been purchased. Two additional, unique capabilities of ICP-MS have also contributed to its commercial success elemental isotope ratio measurements and convenient semiquantitative analysis. The relative sensitivities from element to element are predictable enough that semiquantitative analysis (with accuracy within a factor of 2 to 5) for up to 80 elements can be obtained using a single calibration solution containing a few elements and a blank solution. [Pg.67]

This isotope of oxygen does not always occur in all natural samples in its usual proportion. Because ofmass-dependentchemical fractionation itis notpossible to distinguish an anomaly in this one isotope from measurement of a single isotope ratio. One must use the the three-isotope plot (see Glossary). Using it one concludes that the different classes of chondritic meteorites differ in their ratio l80/170. [Pg.99]


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