Aerosol MALDI of peptides and proteins in an ion trap mass spectrometer: Trapping, resolution and signal-to-noise

The aerosol MALDI technique has been noted for its extreme sensitivity. Unfortunately, resolution and signal quality remain as issues that limit the applicability of the technique. Utilizing the aerosol MALDI technique in an ion trap mass spectrometer has an advantage because the resolution and signal-to-noise ratio are not products of the laser ablation event. In this study, the mass dependence of the aerosol MALDI technique in a constant frequency, 1 MHz, ion trap was explored in terms of trapping, resolution and signal-to-noise. Mass resolution exceeding 5000 was achieved for substance P. Trapping and detection of ions up to myoglobin, m/z 16.9 kDa, was demonstrated. The effect of the pseudo-potential well depth at ejection on resolution and signal-to-noise was revealed. Our results show that the ability to trap large ions with the aerosol MALDI technique can be modeled with the MALDI-induced velocity distribution and the trapping pseudo-potential well depth.