William David Reents

Simultaneous Elemental Composition and Size Distributions of Submicron Particles in Real Time Using Laser Atomization Ionization Mass Spectrometry

Composition and size of individual submicron particles have been measured using a laser atomization ionization mass spectrometry technique, the Particle Blaster. Individual particles are quantitatively converted to atomic cations, providing information on both their complete elemental composition and particle size. Measured average atomic ratios for 100 nm particles of sodium chloride is 1.12 +- 0.36 (Cl:Na), for 50 nm particles of silica is 1.93 +- 0.52 (O:Si), and for 64 nm polystyrene latex spheres (PSL) is 1.13 +- 0.19 (H:C), in excellent agreement with the empirical formulae. Calculated particle sizes agree well with electrostatic classifier or TEM measurements in the size range of 17-900 nm diameter for particles of sodium chloride, silicon, and PSL. Size distributions are also obtain able, giving narrower distributions than are measured with an electrostatic classifier, for particles of alumina, silica, sodium chloride, and PSL spheres. Comparison with TEM data shows comparable primary particle sizes, but numerous particle aggregates are detected by the Particle Blaster which are unreported by the TEM measurements.

High pressure chemistry in a Fourier transform ion cyclotron resonance mass spectrometer using a split-pair magnet

A new experimental method has been developed to probe ion/molecule reactions at gas pressures up to 0. 1 torr. A Fourier transform ion cyclotron resonance (FTICR) mass spectrometer has been constructed to trap ions within the trapped ion cell at these pressures for time intervals up to several hundred milliseconds, allowing the ions to undergo several million collisions. Multiple pulsed valves inject the gaseous reagents in brief, high pressure bursts. A unique, high conductance vacuum chamber rapidly reduces the gas pressure from as high as 0.01 torr to near background pressures in 2–5 s for optimum operation of the FTICR for identifying the ionic products. A pressure of 0.1 torr is attainable but results in slower gas evacuation. High pressure operation of this instrument is demonstrated for ion chemistry in silane, argon, and silicon tetrafluoride. Pressures are sufficiently high to allow termolecular formation of adducts with the trapped ion cell. Negative ion formation in silane has greatly improved efficiency due to the high pressure ionization. Trace impurities at the ppm level in argon and silicon tetrafluoride are detected through chemical ionization afforded by the large number of ion/molecule collisions.