Typical quadrupole mass spectrometers used in ICP-MS have resolutions between 0.7 – 1.0 amu. This is sufficient for most routine applications. However, there are some instances where this resolution is NOT sufficient to separate overlapping molecular or isobaric interferences from the elemental isotope of interest. Table 1 below shows some commonly occurring interferences that make ultratrace determinations of several important elements difficult, particularly in specific matrices. The resolving power (R) of a mass spectrometer is calculated as R = m/(|m1-m2|) = m/∆m, where m1 is the mass of one species or isotope and m2 is the mass of the species or isotope it must be separated from; m is the nominal mass.