Larmor Precession: Observation and Utilization for Boosting the Signal Intensity of Radio Frequency Glow Discharge Mass Spectrometry.

ABSTRACT

A novel magnet array system was constructed to use Larmor precession for boosting the signal intensity of rf-GD-MS. The enhancement mechanism with four magnet array devices of a single-block magnet and 2 × 2, 3 × 2, and 3 × 4 magnet arrays was simulated and studied by COMSOL Multiphysics Software 5.4.0 (COMSOL) to determine if the electrons in the discharge plasma could perform Larmor precession along the direction perpendicular to the magnetic field. Induced by Larmor precession, inelastic collisions between the primary electrons and the sample produced numerous secondary electrons and further improved the ionization efficiency. Moreover, the fuzzy synthetic evaluation result predicted that the device with a 3× 2 magnet array would display the greatest enhancement effect among the four devices. On the basis of these theoretical studies, a magnet array system with four magnet array devices was fabricated and utilized for studies of two scintillation crystals BGO and PWO. The observations indicated that the signal intensities obtained for 209Bi and 208Pb with the magnet array system were 630-3600 times of that obtained without a magnet and were enhanced by a factor of 1.5-2.8 compared with a previously reported stacked magnetic device. Two NIST samples were used to validate the method, and the results suggested that relative errors were less than 10%, and the lowest detection limit for the 3 × 2 magnet array could reach 0.0032 µg·g-1. Furthermore, the magnet array enhancement system with Larmor precession offers an efficient and sensitive approach for direct analysis of nonconducting materials.