An ion source with which ions produced by electrospray can be subjected to ion/molecule reactions at intermediate pressures (10–100 Torr). Deprotonation of polyprotonated peptides

Abstract

Ions produced by electrospray at 1 atm pressure are transferred by means of a small bore capillary to a cylindrical reaction chamber of ≈ 5 cm length which is attached to the inlet of a triple quadrupole mass spectrometer. The reaction chamber pressure can be maintained between 10 and 100 Torr and reagent gases can be introduced in flow through the chamber. When protonated bases BH + are produced by electrospray, proton transfer to a stronger reagent gas base such as tributylamine (TBA) can be initiated in the reaction chamber. Also, polyprotonated peptides such as polyprotonated cytochrome C can be partially deprotonated in the presence of TBA. The intensities of the mass-analyzed ions after reactive changes are still very high, up to 5 × 10 5 counts s −1, and therefore the reaction chamber is very useful for reactive preparation of ions which are to be studied by collision-induced dissociation. The chamber is less well suited for studies of reaction rates and equilibria but the present preliminary design provides information on flow conditions inside the reactor and required changes that would make rate and equilibria studies possible. The question regarding the dependence of the rate constant, k, for proton transfer from multiply protonated peptides on the number of protons present is examined.