AN ELECTROSTATIC ION TRAP MASS SPECTROMETER UTILIZING AUTORESONANT ION EXCITATION AND METHODS OF USING THE SAME

Methods of operation of electrostatic ion trap mass spectrometers in which ions are autoresonantly driven at selected higher integer (>2) multiples of ion oscillation frequencies are provided. Excitation at multiples higher than the fundamental or double the fundamental ion oscillation frequency significantly improves both signal intensity and mass resolution. Each method allows excitation exclusively at one selected frequency that is an integer multiple of an ion's natural oscillation frequency, and thereby virtually eliminates ion excitation at unwanted harmonic frequencies. The resultant mass spectra are therefore clean, and do not display spectral features associated with rf excitation at unintended multiple harmonic frequencies. This has been demonstrated explicitly for 4× and 6× modes, and it is fully implementable at any odd or even multiples of ion oscillation frequencies. With implementation of a new method, mass spectrometers can be operated at faster mass scan rates, giving faster response times, without degradation of signal to noise or resolution over the existing technology instruments. Equivalently, with implementation of a new method, mass spectrometers can be operated with superior signal to noise ratios without degradation of response times or resolution.