Resonant excitation in a low-pressure linear ion trap.

It has been shown that through the process of resonant excitation the fragmentation of ions confined in a low-pressure (<0.05 mTorr) linear ion trap (LIT) can be accomplished while maintaining both high fragmentation efficiency and high resolution of excitation. The ion reserpine, 609.23 Da, has been fragmented with efficiencies greater than 90% while a higher mass ion, a homogeneously substituted triazatriphosphorine of mass 2721.89 Da, has been fragmented with 48% efficiency. This was accomplished by extended resonant excitation by low-amplitude auxiliary RF signals. Computer modelling of ion trajectories and analysis of the trapping potentials have demonstrated that a reduction in neutralization of ions on the rods (or losses on the rods) and increased fragmentation is a consequence of higher order terms in the potential introduced by the round-rod geometry of the LIT.

Carbon-14: direct detection at natural concentrations.

The (14)C atoms naturally present in a piece of 19th-century wood have been detected directly by means of a tandem Van de Graaff accelerator used as a high-energy mass spectrometer. The (14)C ions were easily resolved from interfering ions with the use of a DeltaE-E detector telescope (this telescope consists of a pair of detectors; one of them measures the specific ionization, DeltaE, and the sum of the signals from both detectors gives the total energy for each ion, ET). The technique offers a number of practical advantages.