Atomic and Unfragmented Molecular Emissions

7 Atomic and Unfragmented Molecular Emissions As mentioned in Section 5.4, the association of a recorded signal to a specific element or molecule can be arrived at by matching the m/q ratio of the signal to isotopic mass values (natural abundances of the elements are presented in Appendix A.2). 

Care must, however, be taken to ensure that the mass scale (or more precisely the m/q scale) of the instrument is well calibrated, and that there are no isobaric interferences under the conditions used (isobaric interferences are covered in Section 5.3.1.3). If there are isobaric interferences, these should be removed using one of the procedures outlined within subsections of Section 5.3.1.3. These include the use of HMR, KE filtering, or peak stripping. 

Confidence in elemental assignment can be assured by comparison of the intensities of signals that can be ascribed to other isotopes of the element of interest, i.e. these intensity ratios should match the natural abundances isotopes listed in Appendix A.2, unless, of course, isotopic enrichment of one form or another has occurred (as is the case in nuclear reactions, extra-terrestrial samples, and so on) or has been applied (isotopic implantation). In the case of mono-isotopic elements such as Fluorine and Aluminum, molecular patterns, or even multiply charged ions, can be used to confirm assigmnents. 

As for molecular secondary ions, the mass is simply the sum of the constituent elements (isotopes) making up the molecule. Assignment can then be relatively straightforward for unfragmented ions or those displaying minimal fragmentation. Greater care must, however, be taken to minimize, or at least understand, the presence of potential isobaric interferences. 

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