Laser-enhanced ionization spectroscopy of sodium atoms in an air-hydrogen flame with mass spectrometric detection

Abstract

Sodium atoms in an air-hydrogen flame at atmospheric pressure have been selectively ionized by laser-enhanced ionization (LEI) spectroscopy, and the resulting ions have been drawn into a vacuum and detected by quadrupole mass spectrometry. A commercial inductively coupled plasma-mass spectrometer, modified for use with a flame rather than an ICP, was used to sample and detect the LEI ions. Following double-resonance LEI using pulsed dye lasers, the detected sodium ion signal was enhanced by a factor of 350 over that induced by thermal ionization alone. Using a 5 mm laser beam diameter, the LEI signal pulse was found to last for 0.54 ms (FWHM). Spatial studies in which the position of the laser beam relative to the mass spectrometer sampler cone was varied, demonstrated that the ions produced by LEI travel with the flame velocity into the mass spectrometer, with no significant losses due to recombination from as far as 13 mm from the interface.