Time-of-flight mass spectrometer
A shift of mass axis that occurs when the temperature of a vacuum container consisting of a vacuum chamber ( 15 ) and IT block ( 16 ) or that of a TOF power unit ( 20 ) for applying an ion acceleration voltage is changed, is respectively measured beforehand, and parameters expressing a transfer function based on its response are stored in a transfer function memory ( 24 ). During an analysis, a mass shift predicting operation section ( 25 ) estimates the current shift length of the mass axis from the current temperatures of the IT block ( 16 ) and TOF power unit ( 20 ) obtained by first and second temperature sensors ( 34 and 35 ) as well as from the two transfer functions stored in the memory ( 24 ). A mass shift correcting section ( 29 ) corrects the mass axis of the mass spectrum according to the estimated shift length. Thus, if the ambient temperature suddenly changes, the shift of the mass axis of the mass spectrum due to the temperature change is corrected with high accuracy, so that a mass spectrum with a high level of mass accuracy can be created.
1. A time-of-flight mass spectrometer in which a mass separation unit forming a flight space designed for ions to fly through, an accelerating electrode for initially accelerating the ions and a detector for detecting the ions are provided within an evacuated vacuum container, where the ions that are initially accelerated by the accelerating electrode and temporally separated according to their mass by flying through the flight space are detected by the detector and a mass spectrum having a mass axis and an intensity axis is created from a detection signal of the ion detector, which is characterized by comprising:
a) a first temperature detecting means for detecting a temperature of the vacuum container;
b) a second temperature detecting means for detecting a temperature of a power unit for applying a voltage to the accelerating electrode;
c) a first memory means for storing information based on a result of a previous measurement relating to a transfer function from a temperature change of the vacuum container and a shift of the mass axis due to a temperature change of the mass separation unit;
d) a second memory means for storing information based on a result of a previous measurement relating to a transfer function from a temperature change of the power unit and a shift of the mass axis due to a temperature characteristic of an output of the power unit; and
e) an estimating operation means for estimating a current shift length of the mass axis by using current temperatures of the vacuum chamber and the power unit obtained with the first temperature detecting means and the second temperature detecting means as well as information relating to the transfer functions stored in the first memory means and the second memory means, respectively.
2. The time-of-flight mass spectrometer according to claim 1 , which is characterized in that each of the two transfer functions is respectively obtained by measuring a step response of the shift length of the mass axis of the mass spectrum to a substantially step-like change in the temperature of the vacuum container and the power unit.
3. The time-of-flight mass spectrometer according to claim 2 , which is characterized in that the information relating to each of the transfer functions stored in the first memory means and the second memory means includes both a proportionality factor of transformation from the monitored temperature change to the mass change and a time constant of the transfer function.
4. The time-of-flight mass spectrometer according to claim 1 , which is characterized in that the information relating to each of the transfer functions stored in the first memory means and the second memory means includes both a proportionality factor of transformation from the monitored temperature change to the mass change and a time constant of the transfer function.
5. The time-of-flight mass spectrometer according to claim 1 , which is characterized in that the estimating operation means estimates a total shift length of the mass axis by summing up the current shift length of the mass axis estimated using the current temperature of the vacuum container obtained with the first temperature detecting means as well as the information relating to the transfer function stored in the first memory means, and the current shift length of the mass axis estimated using the current temperature of the power unit obtained with the second temperature detecting means as well as the information relating to the transfer function stored in the second memory means.
6. The time-of-flight mass spectrometer according to claim 1 , which is characterized by further comprising a data processing means for creating a mass spectrum with a corrected mass axis, using the shift length of the mass axis estimated by the estimating operation means.
7. The time-of-flight mass spectrometer according to claim 1 , which is characterized by further comprising an annunciating means for informing users if the shift length of the mass axis estimated by the estimating operation means exceeds a predetermined tolerance level.