Dynamic Range Extension in Glow Discharge Quadrupole Ion Trap Mass Spectrometry

Methods of extending the dynamic range of the quadrupole ion trap have been investigated by utilizing ions generated from a radio frequency powered glow dicharge. The success of the glow discharge quadrupole ion trap technique for inorganic analysis is largely dependent upon increasing the dynamic range. The dynamic range has been increased to 10⁵ by selective accumulation methods which isolate ions over a small mass region of interest. To accumulate selectively ions of interest, static and dynamic electric fields were applied so that, as all ions were gated into the trap, only the ions of interest were retained. Selective accumulation methods employed include mass-selective instability, single-frequency resonance ejection, combination rf-dc, and entrance end cap dc. These methods, capable of being used alone or in combination, were evaluated with respect to ion-trapping efficiency and linearity of signal response with respect to the injection period. Linear injection curves were obtained, and the ability to couple sequential selective ion accumulation methods into a multiple ramp scan function for multielement quantification was demonstrated.