Application of a multi-turn time-of-flight mass spectrometer, MULTUM II, to organic compounds ionized by matrix-assisted laser desorption/ionization

The circuit shape of the ion path, or the multi-turn, provides a solution for achieving unrestricted mass resolution from time-of-flight mass analyzers. The potential of a multi-turn type mass spectrometer, the MULTUM II, with a 1.308 m circuit controlled by four toroidal electric sector fields in biological applications was examined. With matrix-assisted laser desorption/ionization, the ion flight of 18 cycles gave a mass resolution of 10,000 for MH+ of protophorphyrin IX. This resolution was correlated with the flight length, and a resolution of 61,000 was achieved for MH+ of angiotensin I after 75 cycles or a 98.75 m total flight. The results demonstrate that the multi-turn mass spectrometer allows not only high resolution but also very high separation of the ions of molecular species from organic compounds.