voltage should be ramped up again to a value favorable for the next steps by no means should the rf voltage be kept that low for a long time because losses of ions may occur one of the endcaps of three dimensional ion traps is usually connected to the outlet of a digital to analog converter dac which in turn is connected to a digital memory the full shape of the smooth dc voltage pulses can be stored in this memory the dc voltages can be varied between zero and 200 volts usually dc voltage pulses of 10 to 30 volts are sufficiently effective some caution has to be paid for the choice of the rf voltage e when the dc is ramped up by ramp g the lower mass storage limit m z cut off shifts a little further towards the isolation window which has to be taken into account in fig4 a complex mixture of ions is presented in the form of a hypothetical mass spectrum in a greatly overloaded ion trap containing about 10 7 ions such a mass spectrum is hypothetical because it cannot be measured by conventional mass spectrometers due to the overloading the lower storage limit m z cut off is shown by the dashed line 20 and the isolation window is marked by the two dashed lines 21 within the isolation window a tiny ion signal is visible making up only fractions of a percent of all ions within the ion trap nevertheless the tiny signal may correspond to about several thousand ions after application of the isolation method according to the invention following the rf and dc voltage ramping according to fig3 the mixture of.