Effect of magnetic field inhomogeneity on exact mass determination in ICR spectrometry

Abstract

At present, in ICR spectrometry increasing interest exists in the development of ICR spectrometers utilizing superconducting solenoid magnets with magnetic field strength up to about 80 kG, which extend the measurable mass range into the region of higher masses. But, due to such high magnetic field strengths, inhomogeneities, which grow in proportion to field strength increasingly affect the accuracy of measurements. Therefore, magnets with the highest possible homogeneous fields are the aim of technical developments. The extent to which it is necessary to improve the homogeneity of solenoid magnets used in ICR spectrometers by the aid of expensive technology in order to achieve a still measurable effect with respect to exact mass determination is investigated in this work. For this purpose, the change of cyclotron frequency due to magnetic field inhomogeneity will be calculated and the resulting difference between measured and actual masses determined. As the mathematical form of this problem is complicated in the frame of classical mechanics, it is advantageous to use a different method. Regarding the quantum mechanical Schrödinger equation of this problem, we calculate the contributions due to inhomogeneity perturbation theoretically with the aid of a wavepacket formalism. The relation between shift of cyclotron frequency and experimental parameters is given and the order of magnitude of the perturbation is estimated for limiting conditions. It is shown that, even in the most unfavorable case, the influence of magnetic field inhomogeneity is negligibly small.