Sonified Signals From a Compact FT-ICR Instrument: A Feasibility Study. I-Data Mapping to an Equal-Tempered Chromatic Scale.

Rationale: Ions trapped within a Penning cell (ICR) travel periodic orbits whose frequencies are dependent on their mass-to-charge ratio and the value of the magnetic field passing through the trap. Fourier transformation (FT-ICR) decomposes the signal induced in the detection circuit by the rotation of the ions in the cell after the application of an excitation signal. The result of this transformation is a set of characteristic frequencies. We were curious to see whether, once lowered by division into the humanly audible domain, they could be converted into musical notes representative of each of the trapped ions.

Methods: Three algorithms, using three different kinds of divisors, either constant or variable, were considered, and the resulting reduced frequencies were compared with those of an equal-tempered chromatic scale, retaining notes with the closest frequencies.

Results: The method was not specific enough to differentiate observed ions with very close frequencies as is the case for quasi-isobaric ions (ions having the same nominal mass but differing by their exact mass). Only ions with unit mass resolution could be translated into musical notes, and sometimes to the same one, especially at the high-mass end. However, using three-note chords, instead of single notes, different sounds could be attributed to all integer ions from m/z 19 to m/z 299.

Conclusion: It is possible to assign musical notes to unit mass resolution ions analyzed in a simple FT-ICR instrument and design simple didactic musical melodies.