Continuous Mass Spectrometric Analysis of Environmental Pollutants Using Surface Ionization

Abstract

An instrument for real-time analysis of trace impurities in air, including particulates was constructed and evaluated. The sampling system impinges a beam of particles and air on a heated Re ribbon and the resulting ions analyzed in a 7.6 cm radius magnetic sector mass spectrometer. Oxygen in the air raises the work function of the Re to about 7.2 eV at 1,000°K allowing analysis of elements and compounds with ionization potentials as high as 8 eV. For some low ionization potential elements, particles containing 1,000 atoms, particle concentrations of less than 1 per cm³ and average concentrations of 10^-12–10^-13 g/m³ can be detected. Organic compounds can have ionization efficiencies as high as 20% and can be detected in concentrations as low as 0.001 ppb. Water is analyzed by forming an aerosol. Alkali metals and other easily ionized metals can be detected at concentrations of 10^-13 g/cm³ of water.