Numerical analysis of segmented-electrode Orbitraps

Utility of Higher Harmonics in Electrospray Ionization Fourier Transform Electrostatic Linear Ion Trap Mass Spectrometry

“…In Fourier transform mass spectrometry (FT-MS), signal harmonics are often regarded as spectral artifacts that provide little to no additional information than that provided by the signals at the fundamental frequencies. , While the harmonic frequencies can be utilized for higher resolution mass measurements, their presence often leads to more complex mass spectra that make data interpretation more difficult and susceptible to identification errors. − The origins of harmonics and their unique spectral signatures in both Fourier transform ion cyclotron resonance (FT-ICR) and Orbitrap analyzers have been described in detail elsewhere ,,− and can be related to imperfections in the physical device, electric field, or sampling. As the mass resolution at the fundamental frequency is often sufficient, and the harmonics are not related to the chemical identity of the ions, their magnitudes are often minimized via precision machining, shimming the electric field, automatic gain control, balancing of the preamplifier gain, precise initial centering of the ion packet along the symmetry axes of the electric and magnetic fields, etc.…”

“…The distinction is made here that the focus of this technical note is on the utility of harmonics, not on the use of frequency-multiplying traps employing frequency-multiple or harmonic detection. For sake of clarification, frequency-multiple detection, ,− wherein multiple (pairs of) detection electrodes are incorporated in the mass analyzer, can also improve the mass resolution and throughput of an FT-based mass analyzer by moving the detected signal magnitude to a higher harmonic of the fundamental ion motion (reduced cyclotron frequency in ICR, or lap frequency in electrostatic traps). While the idea is decades old, the widespread adoption of frequency-multiplying traps has been limited by the precision to which these traps need to be constructed and operated, without which this detection scheme can produce many higher order, fractional, and/or combination harmonics. , Additionally, in the case of ICR, because the magnitude of the n th order frequency-multiple signal increases as the n th power of ICR postexcitation radius, it is necessary to excite ions to a large radius to avoid large reductions in the observed signal.…”