A new, simple, compact GD-MIP tandem ion source for elemental time-of-flight mass spectrometry

The research objective of this work is to develop a new type of ion source for elemental mass spectrometry. In this work, a simple glow discharge (GD) device has been set up and coupled with a microwave induced plasma (MIP) source to form a so-called "tandem source". In the tandem source, the first source (GD) serves to provide free sample atoms produced by cathode sputtering and partial ionization, and the second source (MIP) serves to enhance the ionization of the free atoms. Since MIP is ordinarily even farther from local thermal dynamic equilibrium than other plasmas, it would seem to be best used in conjunction with another source that is capable of more efficient sample atomization, such as glow discharge. The design and construction of such a tandem source has been performed in our laboratory, and the source has been coupled to a self-assembled time-of-flight mass spectrometer (TOFMS). Primary examinations of operational parameters are pursued. Significant signal enhancement is observed with a microwave power of 15 W, discharge voltage around 420 V, and working pressure of 2.0 Torr. The analytical performance of the new tandem source with and without microwave discharge boosting is compared. Some synergistic benefits derived from the tandem source are discussed. For the isotopes studied, enhancement factors of 3-4 are achieved.