Atmospheric sampling glow discharge ionization (ASGDI) using a quarter-sized cylindrical ion trap mass spectrometer (CIT-MS) for explosives detection in air
A glow discharge source in both the atmospheric sampling glow discharge ionization (ASGDI) mode and the glow discharge electron impact (GDEI) mode interfaced with a miniature (ro=2.5 mm) cylindrical ion trap (CIT) mass spectrometer (MS) has been demonstrated. Reproducible, negative mode ASGDI spectra of saturated headspace perfluoro-1,3-dimethylcyclohexane (PDCH) have been recorded on a home-built quarter-sized cylindrical ion trap mass spectrometer (CIT-MS). The fragment ions m/z 169 and m/z 181 were observed. The total abundance as a function of CIT float voltage was a maximum at 5 volts. This suggests the mean kinetic energy of the ASGDI is near 5 eV. The m/z 169 is the base peak which matches similar PDCH mass spectra from a Griffin miniature CIT-MS. Qualitative and quantitative, positive mode, GDEI mass spectra for toluene have been recorded. Qualitative GDEI mass spectra in continuous glow discharge and pulsed glow discharge have recorded. Pulsed GDEI eliminates photonic noise during detection. Electrons from the ASGDI added noise to the baseline. Electron suppressor plates reduced electrons so that a six-fold increase in signal-to-noise was observed. GDEI mode is suitable for extended, remote use with oxidizing samples under high vibration or high pressure conditions.^
Graham R. Cooks, Purdue University.