Space Charge Effects in Fourier Transform Mass Spectrometry. Mass Calibration

A new relationship between Ion mass and effective cyclotron frequency Is derived for Ions stored In a cubic cell and detected by using Fourier transform mass spectrometry. An assessment of collisional damping on mass measurement error is also made. It Is concluded that frequency perturbation by collisional damping, while predicted by the model, is negligible at sufficiently low pressure. The mass calibration law Is tested at a magnetic field of 1.2 T by using major fragment Ions of 1,1,1,2-tetrachloroethane. with broad band “chirp” excitation of Ions, systematic rather than random errors were discovered. The magnitude of these systematic errors increased as the number of Ions stored In the cell was Increased. However, It Is predicted from the calibration law that errors will decrease with the square of the magnetic field strength.