John Nathan Louris

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.

Injection of ions into a quadrupole ion trap mass spectrometer

Abstract High quality mass spectra can be recorded by generating ions using electron impact ionization or laser desorption, and injecting them into a Paul type quadrupole ion trap. Injection is accomplished at energies of 10–25 eV. The injected ions lose kinetic energy to the damping gas (helium, neon, argon or xenon) and are thus trapped. The efficiency of trapping is investigated as a function of the radio frequency voltage for ions of several masses. Trapped ions can be studied in the usual ways, including photodissociation, collisionally activated dissociation and ion/molecule reactions.

Photodissociation in a quadrupole ion trap mass spectrometer using a fiber optic interface

Abstract A simple fiber optic interface which allows photodissociation in an ion trap mass spectrometer (ITMS) is reported. Photodissociation efficiencies can exceed 95% with performance in this MS/MS mode being comparable or superior to collision-activated dissociation. Comparison of the two activation techniques in causing dissociation of C3F6+. supports the earlier proposal that F. loss occurs from an isolated, electronically excited state. Photodissociation of protonated benzaldehyde shows a different product ion distribution from the one obtained by collisional activation, an effect which is associated with the method of activation and the amount of energy deposited.