Corona discharge ionization

Another big advance in the appHcation of ms in biotechnology was the development of atmospheric pressure ionization (API) techniques. There are three variants of API sources, a heated nebulizer plus a corona discharge for ionization (APCl) (51), electrospray (ESI) (52), and ion spray (53). In the APCl interface, the Ic eluent is converted into droplets by pneumatic nebulization, and then a sheath gas sweeps the droplets through a heated tube that vaporizes the solvent and analyte. The corona discharge ionizes solvent molecules, which protonate the analyte. Ions transfer into the mass spectrometer through a transfer line which is cryopumped, to keep a reasonable source pressure. 

S.J. Taylor, R.B. Turner and P.D. Arnold, Corona-discharge ionization source for ion-mobility spectrometer, PCT Int. Appl. 1993, 32 pp. CODEN PIXXD2 WO 9311554 A1 19930610... 

A.J. BeU and S.K. Ross, Reverse flow continuous corona discharge ionization. International Journal of Mass Spectrometry 218(2) (2002) LI—L6, also found in part at International Journal for Ion Mobility Spectrometry 5(3) (2002) 95—99. 

M. Tabrizchi, T. Khayamian and N. Taj, Design and optimization of a corona discharge ionization source for ion mobility spectrometry. Review of Scientific Instruments 7 (2000) 2321—2328. 

FIGURE 8.6 Corona discharge ionization cascade in positive (a) and negative (b) ion modes. (Reproduced from Raffaelli, A., Atmospheric pressure chemical ionization (APCI), in Cappiello, A. (ed), Advances in LC-MS Instrumentation, vol. 72 (Journal of Chromatography Library), Elsevier, Amsterdam, the Netherlands, 2007, 11-25. Copyright 2007. With permission from Elsevier.)... 

Electrical charges are produced on the metal-semiconductor interface and on the outer surface of the semiconductor, by means of a corona discharge (ionization of the air by high voltage). 

F.S. Pullen, D.S. Ashton, M.A. Baldwin, Corona-discharge ionization LC-MS interface for target compound analysis, J. Chromatogr., 474 (1989) 335. 

Different from the El source, the APCI source contains a heated vaporizer which facilitates rapid desolvation/vaporization of the droplets by a very brief heating period up to 500 °C. Reagent ions obtained from the solvent vapour by a corona discharge ionize the vaporized sample molecules through an ion—molecule reaction. Chemical ionization of sample molecules is very efficient due to the numerous ion—molecule collisions (Figure 16.23). This technique leads to multicharged ions of type (M-F nH)"+ by proton transfer (in the positive mode). Unfortunately this technique is difficult to miniaturize as the required flow rate is higher than that of the electrospray and as such is convenient only for volatile and thermally stable molecules of mass less than 1000 Da. 

Bell, A.J. Ross, S.K., Reverse flow continuous corona discharge ionization, Int. J. Ion Mobil. Spectmm. 2002,5, 95—99. 

An, Y. Aliaga-Rossel, R. Choi, R Gilles, J.-P, Development of a short pulsed corona discharge ionization source for ion mobility spectrometry. Rev. Sci. Instrum. 2005, 76, 085105/1-085105/6. 

The extension of IMS to pharmaceutical applications was a natural progression from its use for illicit drug detection. Many pharmaceutical compounds are basic and thus have high proton affinities, providing both sensitivity and selectivity in a Ni ionization source or a corona discharge ionization source. In addition, the development of stand-alone ESI-IMS provides an efficient introduction and ionization method for nonvolatile pharmaceuticals such as those with high molecular weights, those that are ionic, and those that may decompose at elevated temperatures. 

The corona discharge ionizes the solvent molecules in the tiny droplets as they pass by a tip held at very high voltage. In turn, the charge is transferred to any analyte molecules present in the solvent stream. 

Sekioka, R., Takayama, Y., Seto, Y, et al., 2007. Detection performance of portable corona discharge ionization type ion mobility spectrometer for chemical warfare agents. Bunseki Kagaku 56, 17-22. 

The formation of molecular beams from nozzles of various shapes has been reported." Campargue ° recommends a short straight capillary with aratio of length to diameter equal to or greater than 2. In our homemade ion source, a 0.3-mm-diameter hole in a flat 1.0-mm-thick stainless-steel disk protected by a gas curtain has proven to be very robust and reliable in experiments with corona discharge ionization and electrospray. 

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