Ion Transfer Efficiency
An experimental examination of ion transmission through the electrode system was performed by spraying a mixture of 10 p.M tetrapropyl-, tetrabutyl-, tetrahexyl-, and tetradodecylammonium bromide in ACN through a pulled nanoESI emitter (5 ^m tip) into the source region (Esource) of the device shown in Fig. 3.1b, c. A Keithley 6487 picoammeter was used to monitor the current impinging on an aluminum slide (Isurface), positioned 1 mm from the exit of E3. The current measured at this surface was compared to the total spray current (Ispray). The magnitude of Ispray was determined by monitoring the voltage drop across a 4.7 MX resistor connected in series between the spray tip and high voltage source and calculating the current passing through the resistor from this value and the resistance, as determined by Ohm’s Law. Unless otherwise noted, the spray tip was inserted 1 cm into Esource and potentials applied to each electrode were identical to those given in Fig. 3.5a-c.