Ion-molecule reactions in dilute ether mixtures diisopropyl ether as a cims reagent syste

The study of di-alkyl ethers as a group by mass spectroscopy has not been extensive. Several ethers, either pure or in dilute mixtures with bulk reagent gases have found limited use as chemical ionization reagent systems, but extensive studies in the ion-molecule chemistry of these ethers at higher source pressures have not been done. The dilution of samples in bulk gases allows mass spectrometric studies of the ion-molecule reactions in systems which would be very difficult to do using the pure sample alone. In these mixtures, both direct electron ionization (EI) of the ether and reactions of the ions of the bulk gas with the neutral ether produce fragment ions which react further with the parent ether. Therefore, an understanding of these reactions is important in the exploration of the possible uses of dilute mixtures of alkyl ethers as chemical ionization (CI) reagents. These reactions have been studied by high pressure mass spectrometric techniques and ion-cyclotron resonance experiments.;In general, the EI fragments of the alkyl ethers react with the neutral ether to produce the protonated parent ether (M + H)$sp{+}$ as the predominant ions at high pressures. The proton affinities of the alkyl ethers are fairly high and these protonated ethers could be used as selective proton transfer reagents similar to NH$sb4sp{+}$. Of the several ethers studied, di-isopropyl ether gave the simplest spectrum under high-pressure conditions and the most abundant (M + H)$sp{+}$ ions. Some of the reactions of the EI fragments to produce the (M + H)$sp{+}$ ion appear to be examples of fast endothermic reactions. These reactions do not appear to be the result of excited species and may be examples of so-called 'entropy-driven' reactions. Rate constants for these reactions were determined and are near the theoretical collision rates.;Dilute mixtures of di-isopropyl ether as CI reagents give simple and predictable spectra resulting from proton transfer reactions with basic samples. Several advantages of this system compared to the more widely-used selective CI reagent, ammonia, are discussed. Comparisons to a similar ether, di-n-propyl ether, as a CI reagent system are made.