A novel electrospray ion source/selected ion flow tube/triple quadrupole detector mass spectrometer has been constructed for the study of the kinetics and product distributions of reactions of a diverse array of electrosprayed ions reacting with neutral molecules. The electrospray source provides a near-universal source for ions of biological and other interests. The operation of the instrument is demonstrated with a selection of reactivity and kinetic measurements and threshold collision-induced dissociation determinations. Reactions investigated include H/D exchange between protonated bradykinin and deuterated ammonia, the protonation of the oligo-nucleotide anion [AGTCTG−5H + ] 5− with HBr, the ozonolysis of Ca 2+ , the reaction of protonated phthalic anhydride with dimethyl disulfide, and the Argon collision-induced dissociation of Ba(C 6 H 6 ) 2+ .