Investigation of Space Charge Interactions Which Arise During Simultaneous Confinement of Positive and Negative Ions in an Ion Trap Mass Spectrometer

✍ Scribed by Mathurin, J.-C.; Grégoire, S.; Brunot, A.; Tabet, J.-C.; March, R. E.; Catinella, S.; Traldi, P.

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 416 KB
• Volume: 32
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/(sici)1096-9888(199708)32:8<829::aid-jms539>3.0.co;2-x

✦ Synopsis

While positive and negative ions are created simultaneously in a quadrupole ion trap during electron ionization, there is a marked preponderance of the former species. With prolonged ionization and a relatively high concentration of substrate molecules, positive ion species of low mass/charge ratio can give rise to space charge potentials that can neutralize and exceed the normal trapping potentials for positive ions of high mass/charge ratio, leading to the ejection of positive ions, but not negative ions, from the ion trap. The onset of space charge is manifested by the ejection of positive ions of m/z > 600 ; as the space charge potential is increased incrementally, ejection of positive ions is extended to those of lower mass/charge ratio, that is, to m/z Á 300. Negative ions are not a †ected by the space charge induced by the positive ions ; within the limits of experimentation, negative ions in the mass/charge ratio range m/z 352-633 remain conÐned within the ion trap and can be ejected during a normal analytical scan. Under the inÑuence of positive ion-induced space charge, there is an enhancement of the storage of negative ions having low values of the trapping parameter These observations can be rationalized using a theoretical q z . approach based on a pseudo-potential well model. Although not investigated here, the simultaneous storage of positive ions and negative ions permits the interactions between these species to be studied.