Characterization of multi-jet electrospray systems

Experimental results obtained in multi-jet mode electrospray are presented for two fluids: propylene carbonate and triethylene glycol, each doped with sodium iodide. No structural features were provided in the electrospray emitting capillary in order to stabilize the multi-jet process. For a low number of jets emitted the meniscus is not bound to the rim of the capillary; however as the number of jets increases the mode becomes the so-called rim-mode electrospray. The data thus obtained shows that in all cases the relationship between current and flow rate observed in single cone-jet mode is maintained in multi-jet mode when the current and flow rate is normalized by the number of jets. The results were obtained here for a range of capillary external diameter and under either vacuum or atmospheric pressure; neither of these aspects influenced the observed relationships. The high accuracy flow metering system used demonstrates that in the multi-jet modes the minimum stable flow rate per cone-jet system is reduced below that observed in the single cone-jet mode. However multi-jet mode is seen to be less stable, in that each jet in multi-jet mode is unable to support the same volumetric flow as in the single jet mode; indeed it appears that there is a maximum total flow that can be maintained in an electrospray, independent of the number of jets through which the flow is achieved. A simple model is presented that links these observations to predict the maximum number of jets that may be obtained in the type of multi-jet processes observed here.