Time-of-flight mass spectrometer

A time-of-flight mass spectrometer including an ion source for ionizing a sample component, a time-of-flight mass spectrometry unit including an ion ejecting unit for ejecting ions generated by the ion source or other ions derived from the generated ions into a flight space, and one or a plurality of ion transport optical elements for transporting the ions while focusing the ions by means of a radio-frequency electric field, the one or plurality of ion transport optical elements being provided between the ion source and the ion ejecting unit, the time-of-flight mass spectrometer comprising:

• a) a voltage generating unit for applying radio-frequency voltage for forming the radio-frequency electric field to each of the one or plurality of ion transport optical elements;
• b) a controlling unit for determining, in response to a mass range designated as an observation target, a radio-frequency voltage applied to each of the one or plurality of ion transport optical elements in each of a plurality of times of measurement using different measurement target mass-to-charge ratio ranges for acquiring a mass spectrum entirely covering a mass-to-charge ratio range of the mass range, and for controlling components to perform the plurality of times of measurement while changing the radio-frequency voltage applied to each of the one or plurality of ion transport optical elements by the voltage generating unit, the controlling unit determining the radio-frequency voltage for each of the plurality of times of measurement to maintain a ratio of times of measurement in which radio-frequency voltage is set so that ion passage efficiency in a low mass-to-charge ratio region is relatively high among the plurality of times of measurement to be substantially constant regardless of a width of the mass range;
• and
• c) a mass spectrum summarizing processing unit for obtaining a mass spectrum corresponding to the mass range by summarizing mass spectrum data pieces obtained by the plurality of respective times of measurement under control by the controlling unit.