REDUCTION OF SPACE-CHARGING IN THE QUADRUPOLE ION-TRAP BY SEQUENTIAL INJECTION AND SIMULTANEOUS STORAGE OF POSITIVELY AND NEGATIVELY CHARGED IONS

Experiments were performed to establish the effects produced by the se quential introduction and simultaneous trapping of large quantities of positive and negative ions in the quadrupole ion trap. Injection cond itions were controlled so that the trap stored only positively charged ions, only negatively charged ions, or both positively and negatively charged ions. Improved peak shapes and mass resolution were observed in positive- and negative-ion mass spectra without loss of ion signal when ions of opposite charge were present in the trap. These results i ndicate that space-charging of the trap can be relieved by the additio n of ions of opposite charge.