Novel experimental arrangement developed for direct fullerene analysis by electrospray time-of-flight mass spectrometry

A novel electrospray setup was found effective for direct analysis of fullerene solutions by electrospray (ES) mass spectrometry. The electrospray capillary needle used for the analysis is equipped with a thin metal (copper, platinum or stainless steel) wire installed inside the capillary. The wire tip protrudes slightly from the capillary end. In this configuration the high electrical field formed by the wire tip stimulates a specific electrospray mode with a fine spray originating from the tip. The correlation of the acquired mass spectra with the magnified view of the spray at the capillary tip was investigated. The effective formation of fullerene ions in both negative and positive ion modes was observed in mass spectra only in the specific case of the electrospray originating from the wire tip. The fullerene di-anions observed in the negative ES mass spectra provide evidence for the electrochemical nature of this process occurring at the ES capillary tip. Observation of fullerene ions in mass spectra obtained using the suggested electrospray arrangement is assumed to be a consequence of the fine spray originating from the sharp metal wire tip. In this case the liquid/metal interface is near the Taylor cone apex.