Monitoring of n -hexane degradation in a plasma reactor by chemical ionization mass spectrometry.

n -Hexane (C 6 H 14 ) removal and conversion are investigated in a filamentary plasma generated by a pulsed high-voltage Dielectric Barrier Discharge (DBD) at atmospheric pressure and room temperature in a dry N 2 /O 2 (20%) mixture with C 6 H 14 . The degradation of n -hexane and the by-product formation are analyzed in real-time using a high-resolution Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometer coupled with Chemical Ionization (CI). As alkanes are reacting slowly with H 3 O + ions, two precursor ions were used: O 2 + to follow the n -hexane mixing ratios and H 3 O + to follow the mixing ratios of organic by-products. As the CI-FTICR technique can work at high mixing ratios, studies were made between 5 and 200 ppm of n -hexane. Absorption spectroscopy is also used to follow ozone and carbon dioxide molecules. We show that the DBD efficiency increases for lower n -hexane mixing ratios and a large number of by-products are identified, with the major compounds being: formaldehyde, acetaldehyde, propanal, carbon dioxide, and carbon monoxide along with nitrate compounds. Based on the nature of the by-products characterized, a mechanism accounting for their formation is proposed.