Proton affinity of peroxyacetyl nitrate sampled by membrane introduction mass spectrometry

Abstract

Peroxyacetyl nitrate (PAN) is a fragile, highly reactive molecule which has proven difficult to characterize by mass spectrometry. This study investigates the use of a membrane introduction system to sample PAN and demonstrates that the molecular ions [MH] , [MH] À and M À * can be generated under chemical ionization conditions. Use of tandem mass spectrometry provides characteristic spectra. These capabilities are applied to generate adduct ions of PAN with reference compounds of known proton affinity. Collision induced dissociation of these ions gives, by application of the kinetic method relationship, an estimated value of 191 AE 3 kcal/mol (798 AE 12 kJ/mol) for the proton affinity of PAN. #

Proton Affinity of Peroxyacetic Acid

“…5,6 Proton affinities computed using the QCISD and QCISD(T) methods as well as a number of model chemistry algorithms yielded consistent results. The most accurate proton affinity, PA CBS-APNO 295K ) -775.4 ( 2.0 kJ mol -1 , lies 22.6 kJ mol -1 below the experimental the value of -798 ( 12 kJ mol -1 measured in the experiments of Srinivasan et al 3 and suggests that neither protonation of peroxyacetic acid nor PAN account for their results. …”

Proton affinity of peroxyacetyl nitrate. A computational study of topical proton affinities

“…For example, cleavage of the O‐5—N‐6 bond required 278 kJ mol −1 at 298 K to form NO 2 + and the less stable isomer of peroxyacetic acid. Cleavage of the O‐4—O‐5 bond to form acetic acid and the more stable C 2 v isomer of NO 3 + required 320 kJ mol −1 at 298 K. The calculated ion dissociation energies were in sharp contrast with the low‐energy CID spectrum5 that showed formation of NO 3 + as the major dissociation of protonated PAN.…”

“…Dissociations of even‐electron ions formed by protonation of PAN can be expected to produce even‐electron fragment ions, as observed in collision‐induced dissociation (CID) spectra at low ion kinetic energies 5. The calculated ion dissociation energies are summarized in Table 2.…”

“…The physiological activity of PAN has been of considerable interest2 because of its toxic effects on cell metabolism 3. Whereas detection of PAN in urban air is often achieved by gas chromatography with electron capture detection,4 there has been some recent interest in using chemical ionization mass spectrometry for PAN analysis 5. To optimize the experimental conditions for positive ion chemical ionization (CI) detection, it is advantageous to characterize the cations formed by protonation of PAN.…”

“…To optimize the experimental conditions for positive ion chemical ionization (CI) detection, it is advantageous to characterize the cations formed by protonation of PAN. The proton affinity of PAN has been estimated recently by Srinivasan et al ,5 who used membrane introduction of an in situ prepared solution of PAN in n ‐dodecane and competitive dissociations of proton‐bound clusters of PAN with reference bases (the kinetic method) 6…”