| Various applications of electrosprays (ES) are studied, including injecting ions and drops from the Taylor-cone of an ionic liquid (IL) into a dielectric liquid. In a quiescent heptane bath the injected current is space-charge dominated, is independent of IL flow rate QIL, and scales algebraically with voltage V, needle-to-extractor distance L, and drop mobility Z, as 1~ZV2/L. This leads to a scaling law of the radius of the IL droplets proportional to V-1 and QIL1/2. When heptane has a free surface, charge drifts onto it, destabilizes it, leading to the formation of a jet that atomizes into monodisperse micron-size insulator drops. These drops are at a constant fraction of the Rayleigh limit, with a diameter DD related to the dielectric flow QD, as ~(QD/I)2/3 and the injected IL current I. Reducing the needle diameters leads to the production of dielectric drop diameters of ``~300nm. An anomaly is observed at low QD and high QIL, when the mean drop charge appears to exceed the Rayleigh limit. Gas phase mobility measurements (IMS) of IL drops after evaporation of the heptane show diameters of 3--25nm, as well as ions, all injected directly by the IL into the insulator.;On another application, Polyethylene-glycol(PEG) ions produced in air by ES are analyzed by tandem IMS-Mass spectrometry (MS). Ammonium-acetate and dimethylammonium-acetate buffers yield high charge states at which PEG ions are stretched into linear configurations. In this regime, ion mobility is uniquely related to mass/charge (m/z), and mobility separation is ineffective. A triethylammonium-formate buffer yields reduced charge states, though much of the reduction takes place in the ion guide to the MS rather than at the ESI source. The distinction between these two charge-reduction mechanisms is difficult without IMS, and is made here for the first time. The ions produced by these buffers populate all possible PEG structures, from linear chains to near-spheres. The structure of ions carrying z charges, first resolved here, includes a single globular center carrying n charges, attached to one or two external linear appendices carrying z-n solvated single charges in a bead on a string configuration. |
