Patent ID: 7456396

Claim:
A method for isolating ions in an ion trap utilizing a DC and/or RF voltage to generate a field having a first amplitude value to contribute to the trapping of ions in the ion trap, the ions to be isolated having a range of mass to charge ratios defined by a low mass to charge ratio limit and a high mass to charge ratio limit, and an initial corresponding range of characteristic frequencies, the ion trap including at least two electrodes, and the method comprising: ejecting substantially all ions outside the range of mass to charge ratios to be isolated by: applying an ejection frequency waveform to at least one electrode, the ejection frequency waveform having at least a first frequency edge and a second frequency edge, and at least the initial corresponding frequencies of the range of ions to be isolated being included in the range of frequencies between the first and the second frequency edges; such that initially all ions with an initial corresponding range of characteristic frequencies between the first and second frequency edges are retained in the ion trap; and prior to removing the ejection frequency waveform, adjusting the trapping field from a second amplitude value to a third amplitude value, the second and third amplitude values selected such that during the adjustment substantially all ions outside the range of mass to charge ratios to be isolated are eliminated from the ion trap.