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

Investigations on ion injection into a laboratory-built quadrupole/ion trap tandem instrument (Nermag R10-10/ITMS Finnigan) with a 90 degrees 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 int o the ion trap by using an electrostatic quadrupolar deflector. The effects of major trapping parameters (i.e. ion injection r.f. level and helium pre ssure) were considered. The injection efficiency of the stable CF3+ (m/z 69 ) fragment ion from FC43 and also those of the m/z 40 and 84 atomic cations of argon and krypton depend upon the injection r.f. level conditions. As e xpected, effects of son-linear resonances were observed during these experi ments. Under certain injection and trapping conditions, ion motion can be s trongly affected, yielding ion ejection, because non-linear fields (resulti ng from device imperfections) are present in addition to the quadrupolar po tential required for ion trapping. The influences of non-linear effects acc ording to their strength were investigated to show the best and worst trapp ing conditions. The nan-linear resonances are characterized by the expected beta(z) values. In order to determine the average internal energy deposite d on the selected polyatomic ions during injection, butylbenzene molecular ions were chosen as a model for internal energy measurement. The effects of the r.f. injection level and helium pressure on the injected ion fragmenta tion were studied. The M+. ions were only observed through a narrow injecti on q(z) window. At low q(z) values, only low critical energy m/z 92 ions we re detected, while the higher critical energy m/z 91 ions were observed at higher q(z) values. Copyright (C) 1999 John Wiley & Sons, Ltd.