To provide a method and a device for mass spectrometry, reducing the manufacturing cost of an interface.
The ions generated at the atmospheric pressure pass through vacuum chambers 4, 6, separated by the first, second, and third fine holes 3, 5, 7 and are guided into an MS section 8 for mass spectrometry. The first vacuum chamber 4 is located adjacently to an atmospheric pressure section, this chamber 4 has no vacuum pump for independent exhaustion, and it is exhausted by a pump common to the second vacuum chamber 6 through a bypass hole 26, provided on a wall having the second fine hole 5. The pressure of the first vacuum chamber 4 can be set to several hundred Pa, and the pressure of the second vacuum chamber 6 can be set to several ten Pa. A solvent is fully desorbed at the ion accelerating voltage of about 100V in the first vacuum chamber 4, and the spread in speed can be suppressed. Ions are accelerated with the voltage of about 10V in the second vacuum chamber 6, and the spread in the speed can be suppressed as low as possible.