Radio Frequency Glow Discharge Mass Spectrometry for the Characterization of Bulk Polymers

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

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.

Pulsed radiofrequency glow discharge time-of-flight mass spectrometry for molecular depth profiling of polymer-based films

We demonstrate the potential of an innovative technique, pulsed radiofrequency glow discharge time-of-flight mass spectrometry, for the molecular depth profiling of polymer materials. The technique benefits from the presence, in the afterglow of the pulsed glow discharge, of fragment ions that can be related to the structures of the polymers under study. Thin films of different polymers (PMMA, PET, PAMS, PS) were successfully profiled with retention of molecular information along the profile. Multilayered structures of the above polymers were also profiled, and it was possible to discriminate among layers having similar elemental composition but different polymer structure.

Determination of Bromine in Flame-Retardant Plastics Using Pulsed Glow Discharge Mass Spectrometry

A series of bromine-containing flame-retardant plastics was used to demonstrate the applicability of pulsed radio frequency glow discharge mass spectrometry to the determination of elements in commercial polymers. The direct analysis of bulk samples produced both atomic and molecular species, allowing elemental identification and molecular characterization. However, the low ion signal intensities hindered quantification. Atomization mechanisms for the plastic samples were studied in detail using scanning electron microscopy and mass spectrometry. Although some thermal desorption was observed, sputter atomization dominated when samples were not subjected to excessive discharge power. The sputter rates of various polymers, as evidenced by sputter weight loss measurements, showed a strong correlation with their ion production capabilities. Sputtering rates were related to the physical and chemical properties inherent to a polymer's composition. Analysis of samples compacted with a silver binder provided intense analyte signals allowing quantitative analysis. Signal stability, measurement accuracy, measurement precision, and detection limits were all assessed.