Electrohydrodynamic ionization

Note EHI has important features in common with ESI i) an electrolytic solution is sprayed by the mere action of an electrostatic field, ii) upon which it forms a mist of electrically highly charged droplets, from which Hi) the analyte ions are liberated into the gas phase for subsequent mass analysis. 

Actually, the development of electrospray ionization itself by the Dole group [45] preceded API, TSP, and EHI by several years [46]. The underlying principle of ESI, which it shares with EHI, even dates back to work by Zeleny [39] and Taylor 

Note It should be emphasized that atmospheric pressure ionization methods differ from all other techniques discussed so far in that they require an uninterrupted flow from ambient pressure into the high vacuum of a mass analyzer. This can only be accomplished by means of powerful differential pumping. 

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Electrospray ionization occurs by the same four steps as listed above for thermospray (see Section 4.6). In contrast to thermospray, and most other ionization methods nsed in mass spectrometry, it shonld be noted that electrospray ionization nnnsnally takes place at atmospheric pressure. A similar process carried out under vacuum is known as electrohydrodynamic ionization and gives rise to qnite different analytical results. This technique has not been developed into a commercial LC-MS interface and will not be considered further. 

Electrohydrodynamic ionization A process in which a high voltage is used to generate droplets from which ions are desorbed under conditions of high... 

The techniques of field desorption (FD) and electrohydrodynamic ionization (EHD) differ from SIMS, LD, and FAB in their physical basis and in features seen in the spectra. For example, the diquaternary ammonium salts discussed above yield intact doubly-charged ions, and fragmentation is less extensive. Nonetheless, the three classes of ions described for molecular SIMS are generally seen in FD (50). An EHD study of a series of diquaternary ammonium salts (51) led to the conclusion that the amount of internal energy deposited in EHD is less than in SIMS and FAB. The same study also indicated that FAB (liquid matrix) deposits less energy than SIMS (solid matrix), so in this case the order of energy deposition is SIMS > FAB > EHD. 

B.P. Stimpson, C.A. Evans, Jr., Electrohydrodynamic ionization MS of biochemical materials, Biomed. Mass Spectrom., 5 (1978) 52. 

Static secondary ion mass spectrometry (SSIMS) 1976 Atmospheric pressure chemical ionization (APCI) 1976 Thermospray (TSP) 1978 Electrohydrodynamic ionization (EH) 1978 Fast atom bombardment (FAB) 1982 Potassium ionization of desorbed species (KIDS) 1984 Electrospray ionization (ESI) 1984 Multiphoton ionization (MPI) 1987... 

Simons DS, Colby BN, Evans CA Jr. Electrohydrodynamic ionization mass spectrometry— the ionization of liquid glycerol and non-volatile organic solutes. Int J Mass Spectrom Ion... 

Stimpson BP, Evans CA Jr Electrohydrodynamic ionization mass spectrometry of biochemical materials. Biomed Mass Spectrom. 1978 5 52-63. 

Simons, D.S. Colby, B.N. Evans, C.A., Jr. Electrohydrodynamic Ionization Mass Spectrometry. Ionization of Liquid Glycerol and Nonvolatile Organic Solutes. Int. J. Mass Spectrom. Ion Phys. 1974,15, 291-302. 

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