Competitive ion kinetics in direct mass spectrometric organic speciation. 1994 Progress report

Abstract

The experimental work on the gas phase proton affinity (PA) scale, discussed in some detail in last year`s Progress Report, will be completed within the next few weeks. Basically this effort involves the development of a precise and accurate interlocking ladder of relative PA`s derived from the temperature dependence of proton transfer equilibria incorporating a variety of reactant pairs using the technique of pulsed high pressure mass spectrometry (NIST has the only US facility). The PA subset under investigation was expanded from the original list to cover the region between CH{sub 3}CHO and (CH{sub 3}){sub 2}CO, which spans a PA range of approximately 12 kcal/mol. More than 300 separate equilibrium measurements have been carried out to date over the temperature range 240--395 C. The thermochemical region under study creates a bridge between the so-called upper and lower PA scales, and includes two primary reference standards, CH{sub 3}CHO and i-C{sub 4}H{sub 8}, with PA`s independently defined elsewhere via photoionization techniques.