Ions generated in both continuous and pulsed-mode external ion sources are injected into an open-ended cylindrical Fourier-transform ion cyclotron resonance ion trap by means of an electrostatic ion guide consisting of concentric cylinder and wire electrodes to which a potential difference is applied. Broadband axialization during ion injection improves ion trapping efficiency by reducing the ion off-axis displacement. Significant improvements in both signal-to-noise ratio and mass resolving power, along with high mass selectivity are demonstrated for ions generated by external Cs+ secondary ion mass spectrometry or by matrix-assisted laser desorption/ionization.