Isotopes spectral differences

In addition, because of the very high resolution achieved, microwave spectroscopy can unambiguously assign rotational spectra for different isotopologues of the same molecule. In the studies of 2-deoxy-ribose and fructose, spectra of and substituted species, either in natural abundance (0.02-1.1%) or in eiuiched samples, could be observed. Since the isotopic spectral modifications are directly connected to the molecular moments of inertia, it is possible to determine experimentally the position of the isotopic substituents in the molecular structure without... 

The concept of selectivity and specificity has been applied to characterize interferences appearing in two different ICP-MS techniques (Horn [2000]). Classical ICP-MS with pneumatic nebulization and ETV-ICP-MS are compared for the determination of traces of zinc in sea-water. Whereas spectral interferences decrease using the ETV device, nonspectral interferences increase significantly (Bjorn et al. [1998]). A quantitative comparison of the both analytical procedures, here called PN (pneumatic nebulization) and ETV (electrothermal vaporization, Sturgeon and Lam [1999]) is possible by means the specificity as a function of the Zn concentration (Horn [2000]). The spectral interferences on the four zinc isotopes are listed in Table 7.4. 

In ultrapure polymer samples, all chains are terminated in the same way. The MALDI spectrum of an ultrapure polymer resembles a comb and the spacing between the comb s teeths equals the mass, Mrepeat, of the repeat unit. This quantity is often diagnostic and it suggests an almost trivial use of MALDI is the spectral identification of polymers. The reason is that, if one computes the M,.c x.at value for common polymers, most values are different, the number of superpositions being very low [4—6]. The Mrepeat value is not an integer, due to the fact that various isotopes are present. 

Another type of non-spectral matrix effect, associated with the oxidation state of the analyte, was proposed by Zhu et al. (2002). Figure 14 plots the relative Fe(II) to total Fe ratio of ultra pure Fe standard solutions versus the difference between the 8 Fe value of the mixed valence state standard and the 5 Fe value of the Fe(III) only standard. The oxidation state of these standards was not quantified by Zhu et al. but based on colorimetric methods using 2,2 -bipyridine the relative Fe(ll) to total Fe ratios of these standards are well known. This matrix effect appears to exert a signihcant control on isotope accuracy, where for example if a reduced ferrous solution was compared to an oxidized ferric standard, the accuracy of the 5 Fe value could be affected by up to l%o. This matrix effect associated with oxidation state is unlikely to be a result of space charge effects because the mass of an electron is unlikely to produce a large change in the mass of the ion beam. Perhaps this matrix effect may be associated with ionization properties in the plasma. 

Some practical aspects of isotopic patterns as commonly observed in mass spectra should now be considered. Although it seems trivial, the first step is the recognition of an isotopic pattern as such, and especially for beginners this is not always easy. Especially if signals from compounds differing by two or four hydrogens are superimposed or if such a superimposition can not a priori be excluded, a careful stepwise check of the observed pattern has to be performed to avoid misinterpretation of mass spectral data. Similar care has to be taken when isotopically labeled compounds are involved. Next, potential pitfalls for the novice, the correct treatment, and the benefits of isotopic patterns are discussed. 

In an analogous manner, this approach is extensible to treat simultaneously data of multiple isotopic variants of a particular diatomic species such a treatment might be based on apphcation of differences of spectral terms according to formula 19, with empirical parameters and A therein as explained at that point. In such a treatment there is convenience in distributing a factor reduced mass p between vibrational and rotational quanmm numbers, or rather their respective functionals, in the following form, known as mass-reduced quantum numbers [68],... 

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