Determination of Precursor Ions

The detector can be hit only by an ion at m/z 67 because Q3 lets no other ions through. An impact with the detector therefore means that a precursor of m/z 67 just passed through Ql. When correlating the impacts on the detector with the U and V values of the potential applied to Ql at the time of the impact, the recorded spectrum displays the precursors of m/z 67. 

FIGURE 5.14 Mass spectrum of molecule M, recorded with scanning of Q1 (Q3 is set in SIM on m/z 67). 

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Grange, A. H., and Sovocool, G. W. (2008). Automated determination of precursor ion, product ion, and neutral loss compositions and deconvolution of composite mass spectra using ion correlation based on exact masses and relative isotopic abundances. Rapid Commun. Mass Spectrom. 22 2375-2390. 

Another scanning technique, the defocusing voltage scan, allows the determination of precursor ions from a given fragment. 

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