A simple glow discharge ion source for direct solid analysis by on-axis time-of-flight mass spectrometry

A simple and small-sized direct current glow discharge (dc-GD) ion source has been designed and constructed for direct analysis of solid samples. The glow discharge (about 100 mm(3) of internal volume) was coupled to a commercial on-axis time-of-flight mass spectrometer (TOFMS) for fast simultaneous multielement-selective detection. The commercial TOFMS used was originally coupled to an inductively coupled plasma (ICP) ion source. Therefore, the GD source presented in this study was designed aiming at being easily exchanged with the ICP source of a commercial ICP-TOFMS instrument (LECO Corporation). The distance between the cathode (sample) and the sampler cone was kept at about 4 mm. The proposed source is able to analyse planar conducting samples of different sizes with good long-term stability (better than +/-5% when isotope ratioing techniques were applied). The spectral mass resolving power was about 1520 (at mass 120 u). Finally, the expected benefits of the fast simultaneous multielemental capabilities of TOFMS detection to carry out direct depth profile analysis of solid samples are demonstrated and discussed.