Performance Evaluation for Thermal Ionization Time of Flight Mass Spectrometer

Thermal ionization mass spectrometry (TIMS) is one of the oldest mass spectrometric techniques, mostly applied in the precise and accurate measurement of isotopic ratios for different elements. Time of flight mass spectrometry (TOF-MS) has an unlimited mass range and an ability to rapidly obtain mass spectra relevant for the fast analysis of transient signals. By combining thermal ionization source with time-of-flight mass spectrometer, a thermal ionization time of flight mass spectrometer (TI-TOF-MS) was self-established. The performance of this instrument and the potential applications were evaluated. Samples were dropped on the metal rhenium, single or triple filament structure was used depend on the analysis element. Ions, produced by ionizing the elements loaded on the filament, pass through the ion focus lens and transport to the time-of-flight mass analyzer for detection. The analysis performance of TI-TOF-MS was comprehensively tested. The instrument has the ability to detect all the elements from m/z 6 to m/z 320, which covers all the elements can be ionized by the thermal ionization source. The resolution of instrument can reach 2 000 at m/z 208. The mass stability of instrument is test in 2 h is 7.76×10^-5 for ²⁰⁸Pb. The precision acquired for ²⁰⁴Pb/²⁰⁶Pb, ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb ratios are 0.85%, 0.27% and 0.55%, respectively, which depend on the calculate method. During the thermal ionization process of uranium, the signal of ²³⁸U⁺、 ²³⁸U¹⁶O⁺ and ²³⁸U¹⁶O₂⁺ were measured on the spectrum. The instrument can also record the change of different kinds of ions. Compare to the commercial instrument, the home made TI-TOF-MS has a large step to grow up. But this instrument is capable for studying the thermal ionization process of different elements, monitoring the purities in the samples, and rapidly detecting the isotope ratio at a low cost. The future work should focus on the improvement of stability and the application on the TI-TOF-MS.