Influence of trapping parameters on ion injection and dissociation efficiencies in a quadrupole mass filter/ion trap tandem instrument

Abstract

Investigations on ion injection into a laboratory-built quadrupole/ion trap tandem instrument (Nermag R10-10/ITMS Finnigan) with a 90Ä geometry are described. The quadrupole dual electron impact/chemical ionization (EI/CI) source was used as an external source to prepare ions under EI (or CI) conditions. They were selected by the quadrupole analyzer and injected into the ion trap by using an electrostatic quadrupolar deÑector. The e †ects of major trapping parameters (i.e. ion injection r.f. level and helium pressure) were considered. The injection efficiency of the stable (m/z 69) fragment ion from FC43 and also those of the m/z 40 and 84 atomic cations of argon CF 3 ' and krypton depend upon the injection r.f. level conditions. As expected, e †ects of non-linear resonances were observed during these experiments. Under certain injection and trapping conditions, ion motion can be strongly a †ected, yielding ion ejection, because non-linear Ðelds (resulting from device imperfections) are present in addition to the quadrupolar potential required for ion trapping. The inÑuences of non-linear e †ects according to their strength were investigated to show the best and worst trapping conditions. The non-linear resonances are characterized by the expected values. In order to determine the average internal energy deposited on the selected polyatob z mic ions during injection, butylbenzene molecular ions were chosen as a model for internal energy measurement. The e †ects of the r.f. injection level and helium pressure on the injected ion fragmentation were studied. The M'ĩ ons were only observed through a narrow injection window. At low values, only low critical energy m/z 92 q z q z ions were detected, while the higher critical energy m/z 91 ions were observed at higher values. Copyright q z