Trace Element Analysis of Potassium by Resonance Ionization Mass   Spectrometry
  A simple resonance ionization mass spectrometer is built with a Quadrupole Mass Spectrometer (QMS) and two laser diodes aiming at trace analysis of potassium. The overall detection efficiency is estimated comparing the yields of resonance ionization and electron-impact ionization in the same QMS. A clear discrimination of $^{39}\rm K$, $^{40}\rm K$ and $^{41}\rm K$ is demonstrated with a help of isotope shifts of the atomic levels. 
Yoshihiro Iwata, Yoshizumi Inoue, Makoto Minowa