Imaging of Focused Ion Stream
The ability to generate, transmit, focus, and detect ions in air with the curved polymeric electrode system was demonstrated by spraying a mixture of tetraalky- lammonium (TAA) bromide salts (10 ^M in acetonitrile) from a nanoESI emitter into the source region (Esource) of the curved electrode. Images of ion intensity at the exit region of the curved electrode system were reconstructed from data obtained by scanning an IonCCDTM detector (OI Analytical, AL, USA) across the exit orifice of the final electrode. In brief, the IonCCDTM was mounted onto a computer controlled moving stage and the detector slit was scanned across the exit of the last electrode at a fixed rate of 0.1 mm/s with the detector integration time set to 100 ms. An illustration of this process is shown in Fig. 3.2.
Throughout this process a potential of 10 V was applied to the IonCCDTM housing. The application of this potential establishes a mild electric field in the space between the electrically floated detector array and the aluminum enclosure (0.711 mm). As a consequence ions are drawn to the detector surface which results in the observation of a more intense signal. A Matlab script was used to extract individual scans taken during the acquisition period and reconstruct these into 2D images of ion intensity on the basis of detector integration time and the moving stage velocity. These values were used to calculate position along the scan axis (Y(t)) for each detection cycle of the IonCCDTM.
Fig. 3.2 Diagram illustrating how IonCCD™ data was captured and the data assembled into a 2D plot of ion intensity from individual integration time steps. The detector slit is indicated by the blue transparent box