Porous graphite sheet spray ionization ion mobility spectrometry

In this work, a porous graphite sheet is introduced as the substrate in a spray ionization source for ion mobility spectrometry (PGSI-IMS) for the first time. This ionization source has some important advantages in comparison with the hollow needle, which is conventionally used in electrospray ionization. In order to prepare the hydrophilic surface needed to load samples on a graphite substrate, the graphite sheet was treated with hot sulfuric acid solution for 2 hours. Some parameters affecting the ionization efficiency were studied, and the optimized conditions were found to be 3.5-kV graphite voltage, 24-μL methanol flow rate, 500 mL min-1 the gas flow rate, and graphite sheet with a 60° tip angle and 3-mm distance from the counter electrode. Finally, analyses of some test compounds (imipramine, diclofenac, codeine, morphine, and ethion) were conducted to evaluate the capability of the new ionization source in the positive and negative modes. The satisfactory results proved the capability of the graphite sheet spray ionization, to be conveniently used for routine analysis of chemical compounds by IMS.