Orthogonal acceleration time-of-flight mass spectrometer

An orthogonal acceleration time-of-flight (oa-TOF) mass spectrometer has an ion source producing ions, a first region of a low degree of vacuum, an ion reservoir, and a second region of a high degree of vacuum. A space for transporting the ions produced by the ion source is placed in the first region. The ion reservoir accelerates the ions transported in from the first region in a pulsed manner and extracts the ions. A time-of-flight mass analyzer for mass separating the ions extracted from the ion reservoir is disposed in the second region, together with the ion reservoir. An isolation valve is mounted in a hole that places the first and second regions in communication with each other to permit the first and second regions to be isolated from each other.