A dynamic reaction cell for inductively coupled plasma mass spectrometry (ICP-DRC-MS) - Part 1. The rf-field energy contribution in thermodynamics of ion-molecule reactions

The existing vast database of ion-molecule reaction kinetics may, with advantage, be used to overcome spectral interference in ICP-MS. To be directly applicable to an rf multipole reactor, it must be shown that the multipole provides a controlled thermal environment. The contribution of the rf field energy to the ion energy is modeled for a quadrupole reaction cell. It is shown that the rf field contribution increases with increasing rf amplitude and decreasing rf frequency (i.e., towards the high-q side of the quadrupole stability region). A thermodynamic ladder is proposed as a convenient measure of the thermal characteristics of the reactor, and should serve as a benchmark for comparison of various reaction cell designs. Experimental results for charge transfer reactions are presented. These indicate that the configuration reported is near-thermal, with an rf field energy contribution less than about 0.4 eV. The rich variety of ion-molecule processes which might be studied is demonstrated by examples of condensation, simple association and complex ligation reactions.