Isotopologs and Accurate Mass

It has been pointed out that routine accurate mass measurements are conducted at resolutions which are normally too low to separate isobaric isotopologs. Unfortunately, multiple isotopic compositions under the same signal tend to distort the peak shape (Fig. 3.31) [64], This effect causes problems when elemental compositions have to be determined from such multi-isotopolog peaks, e.g., if the mono-isotopic peak is too weak as in case of many transition metals. Generally, the observed decrease in mass accuracy is not dramatic and is somewhat counterbalanced by the information derived from the isotopic pattern. However, it can be observed that mass accuracy decreases by about 50% on such unresolved signals. 

If isotopolog ions are resolved or if certain isotopologs are free from interference, and provided sufficient mass accuracy is available, the distance between isotopic peaks can yield a new type of analytical information. As are the isotopic masses themselves, the differences between isotopic masses are characteristic for certain elements. Boron for exanple, has a small mass difference of just 0.9964 u 

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