ION ISOLATION AND SEQUENTIAL STAGES OF MASS-SPECTROMETRY IN A QUADRUPOLE ION TRAP MASS-SPECTROMETER

Sequential reactions with as many as eleven steps (MS12) are accomplished with a quadrupole ion trap mass spectrometer. Both collision induced dissociation and ion/molecule reactions can be utilized in these reaction sequences. The isolation of intermediate products is performed extremely rapidly through the application of a combination of d.c. and r.f. potentials to give, to the ions of interest, coordinates near a cusp of the stability diagram (az = 0.150, qz = 0.781). The ion yields and signal-to-noise (S/N) ratios can be quite high for each individual step, resulting in good ultimate yields and S/N ratios even after multiple reaction steps. The scan functions used are investigated in detail by exploring the ejection of xenon isotopes in experiments which reveal the shape of the stability diagram in the cusp region. The resolution of the isolation procedure is investigated. These ion isolation capabilities are applied in a series of steps to cause extensive dissociation of the saturated sterane, cholestane, to yield a stable aromatic ion, C6H+5, and to demonstrate that the m/z 79 fragment of dimethylpyrrole is protonated benzene. They also allow multiple charge exchange and dissociation reactions to be performed in sequence on a single population of molecular ions. © 1990.