Patent ID: 7928373

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 first mass to charge ratio limit and a second mass to charge ratio limit, and an initial corresponding range of characteristic frequencies, the characteristic frequencies comprising frequency components of a first dimension and frequency components of a second dimension, the ion trap including electrodes comprising electrodes aligned along the first dimension and electrodes aligned along the second dimension, the method comprising: ejecting substantially all ions outside the range of mass to charge ratios to be isolated by: applying a first portion of an ejection frequency waveform across the electrodes aligned to the first dimension, the first portion of the ejection waveform comprising at least a first frequency edge and a second frequency edge in the first dimension, and at least the initial corresponding range of characteristic frequencies in the first dimension of the range of mass to charge ratios to be isolated are included in the range of frequencies between the first edge and the second edge; applying a second portion of the ejection frequency waveform across the electrodes aligned to the second dimension, the second portion of the ejection frequency waveform having a third frequency edge and a fourth frequency edge in the second dimension, and at least the initial corresponding frequencies in the second dimension of the range of ions to be isolated are included in the range of frequencies between the third edge and the fourth edge; wherein the first portion of the ejection frequency waveform is composed of a first set of component frequencies and the second portion of the ejection frequency waveform is composed of a second set of component frequencies different from the first set.