The site of protonation of a substituted benzene may be determined using chemical onization mass spectrometry with D20 as a reagent gas. The observation of extensive exchange

Ion cyclotron single- and multiple-resonance spectroscopy have been used to identify and examine the energetics of ion-molecule reactions in which H3O+ and H3S+ are involved either as product or reactant. The reactions observed provide narrow limits for the gas-phase proton affinities of these species, giving 164 ± 4 kcal/mole for H2O and 178 ± 2 kcal/mole for H2S.

A new methodology for comparative bioavailability testing is described in which each drug formulation is compared with a stable isotope-labeled variant of the drug that is consumed orally in solution at the same time the tested formulation is ingested. The methodology is used to determine the comparative bioavailabilities of two commercially available brands of imipramine hydrochloride. The power of the new methodology to detect differences between drug formulations, when, in fact, such differences exist, is shown to be superior to that of conventional bioavailability tests.

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