| CPC H01J 49/0036 (2013.01) [H01J 49/0031 (2013.01); H01J 49/401 (2013.01)] | 9 Claims |

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1. A time-of-flight mass spectrometer having a measurement unit which includes a flight-field creation section configured to create, within a flight space, an electric field for causing ions to fly, and an ion acceleration section configured to accelerate ions which are a measurement target and to send the ions into the flight space, the time-of-flight mass spectrometer comprising:
a data-analysis processor configured to create a spectrum based on data acquired by the measurement unit, the spectrum showing a relationship between ion intensity and time of flight or mass-to-charge ratio;
an index calculator configured to calculate, as an index concerning a peak observed in the spectrum, a difference in time of flight or mass-to-charge ratio between a midpoint of a first peak width at an intensity which equals a top intensity of the peak multiplied by a first ratio and a midpoint of a second peak width at an intensity which equals the top intensity of the peak multiplied by a second ratio which is smaller than the first ratio; and
an evaluation result storage section configured to evaluate a degree of symmetry of the peak from the index and to store an evaluation result.
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