Ion and Droplet Mass Measurements of an Electrospray Emitter using an ExB Filter

Ion and droplet mass-to-charge measurements of electrospray from a single emitter tip were taken using an ExB type filter. The propellant used was the ionic liquid 1Ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4), which has three distinct anion species, BF4 , [EMI + ] [BF4 ]2, [EMI + ]2 [BF4 ]3 during electrospray operation. Theoretical calculations show that the ExB filter would be able to resolve three anion species and the coincidently extracted droplets during a voltage sweep of the electrodes. The results from the experiment show peaks corresponding with the theoretical values of 87, 287, and 485 amu/e for the three BF4 anion species, respectively, within experimental error. A broad peak was also observed at 6258 amu/e with a width of 6487 amu/e that corresponded to the range expected for droplets emitted at varying charge. Varying systematic errors were observed during the experiment, but remained consistent within a given test. Therefore, calibration factors based on the difference in the measured and theoretical potential on the ExB deflection electrodes for a given mass-to-charge ratio was determined for each test, which reduce the disagreement to within ±3% of the theoretical values. Proportional trend between the magnitude of the current peaks and the flow rate of the supplied EMI-BF4, and the magnitude of the current peaks and the extraction voltage were also observed. Based on the number of peaks observed during operation at various flow rates, it was also found that the electrospray was operating in both the pure ion and ion-droplet regimes.