Identification of harmonics in RF quadrupole Fourier transform mass spectra

A method of performing mass spectrometry, comprising:

• introducing a plurality of ions generated by ionizing a sample into a Fourier transform mass analyzer,
• radially confining said ions using at least a first radial confinement parameter,
• applying an ion excitation signal to radially excite at least a portion of said ions to cause said ions to exhibit radial oscillations at secular frequencies thereof, wherein said radially excited ions interact with fringing fields in vicinity of said exit port such that said radial oscillations are converted into axial oscillations,
• detecting at least a portion of the axially oscillating ions exiting the mass analyzer,
• determining a mass spectrum of said detected ions,
• modifying said at least first radial confinement parameter to obtain a second radial confinement parameter,
• introducing a second plurality of ions generated by ionizing said sample into the Fourier transform mass analyzer,
• radially confining said second plurality of ions using said second radial confinement parameter,
• applying an ion excitation signal to radially excite at least a portion of said second plurality of ions so as to cause said second plurality of ions to oscillate radially at secular frequencies thereof, wherein said radially oscillating ions interaction with the fringing fields in the vicinity of said exit port such that the radial oscillations are converted into axial oscillations,
• detecting at least a portion of the axially oscillating ions exiting the mass analyzer,
• determining a second mass spectrum corresponding to said detected axially oscillating ions,
• comparing said first and second mass spectra to identify spurious mass signals.

A method of performing mass spectrometry, comprising:

• generating a plurality of ions exhibiting a distribution of m/z ratios,
• introducing said ions into a mass filter to remove ions having m/z ratios above or below a threshold m/z ratio,
• introducing the remaining ions into a Fourier transform (FT) mass analyzer comprising a plurality of rods arranged in a multipole configuration, said plurality of rods comprising an input port for receiving ions and an output port through ions can exit the mass analyzer,
• applying at least one RF voltage to at least one of said rods so as to generate an RF field for radial confinement of the ions as they pass through the multipole rod set,
• exciting radial oscillations of at least a portion of ions in said FT mass analyzer at secular frequencies thereof such that fringing fields in proximity of the output end of said plurality of rods convert said radial oscillations of at least a portion of said excited ions into axial oscillations as said excited ions exit the multipole rod set, and
• detecting at least a portion of said axially oscillating ions exiting the multipole rod set to generate a time-varying signal,
• obtaining a Fourier transform of said time-varying signal to generate a mass spectrum of said remaining ions,
• wherein said threshold for removing ions is selected so as to reduce occurrence of spurious harmonics of mass signals or to facilitate detection of said spurious harmonics in the mass spectrum.