Van de Graaff generator
Other electrostatic machines like the Wimshurst machine or Bonetti machine work similarly to the Van De Graaff; charge is transported by moving plates, disks, or cylinders to a high voltage electrode. For these generators, however, corona discharge from exposed metal parts at high potentials and poorer insulation result in smaller voltages. In an electrostatic generator, the rate of charge transported (current) to the high-voltage electrode is very small. After the machine is started, the voltage on the terminal electrode increases until the leakage current from the electrode equals the rate of charge transport. Therefore, leakage from the terminal determines the maximum voltage attainable. In the Van de Graaff generator, the belt allows the transport of charge into the interior of a large hollow spherical electrode. This is the ideal shape to minimize leakage and corona discharge, so the Van de Graaff generator can produce the greatest voltage. This is why the Van de Graaff design has been used for all electrostatic particle accelerators. In general, the larger the diameter and the smoother the sphere is, the higher the voltage that can be achieved.
Electrostatic spray ionization
Electrostatic spray ionization (ESTASI) is an ambient ionization method for mass spectrometry (MS) analysis of samples located on a flat or porous surface, or inside a microchannel. It was developed in 2011 by Professor Hubert H. Girault’s group at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. In a typical ESTASI process, a droplet of a protic solvent containing analytes is deposited on a sample area of interest which itself is mounted to an insulating substrate. Under this substrate and right below the droplet, an electrode is placed and connected with a pulsed high voltage (HV) to electrostatically charge the droplet during pulsing. When the electrostatic pressure is larger than the surface tension, droplets and ions are sprayed. ESTASI is a contactless process based on capacitive coupling. One advantage of ESTASI is, that the electrode and sample droplet act contact-less avoiding thereby any oxidation or reduction of the sample compounds at the electrode surface, which often happens during standard electrospray ionization (ESI). ESTASI is a powerful new ambient ionization technique that has already found many applications in the detection of different analytes, such as organic molecules, peptides and proteins with molecule weight up to 70 kDa. Furthermore, it was used to couple MS with various separation techniques including capillary electrophoresis and gel isoelectric focusing, and it was successfully applied under atmospheric pressure to the direct analysis of samples with only few preparation steps.