Focussing errors of a multiple-focussing time-of-flight mass spectrometer with an electrostatic sector field

Abstract

The second-order focussing errors in time and space of a multiple-focussing time-of-flight mass spectrometer are calculated. Dispersion in time of flight and mass resolution are derived as functions of the relative spread of the initial energy (δ) and of the radial and axial aperture angles (α 0, β 0). The dimensions of the entrance slit ( u 0, v 0) and the original ion pulse length (Δ t i) are additional parameters. For a typical instrument with 157-cm equivalent path length, 500-eV ion energy, δ = ±5%, α o = β o = ± 1.3°, and Δ t i = 65 ns, a resolution of 150 is obtained. For α o = ±1.3°, β o = ±1°, δ = ±2.25% and Δ t i = 10 ns, the resolution increases to 430.