Analysis of α-acyloxyhydroperoxy aldehydes with electrospray ionization-tandem mass spectrometry (ESI-MSn)

A series of a-acyloxyhydroperoxy aldehydes was analyzed with direct infusion electrospray ionization tandem mass spectrometry (ESI/MSn) as well as liquid chromatography coupled with the mass spectrometry (LC/MS). Standards of a-acyloxyhydroperoxy aldehydes were prepared by liquid-phase ozonolysis of cyclohexene in the presence of carboxylic acids. Stabilized Criegee intermediate (SCI), a by-product of the ozone attack on the cyclohexene double bond, reacted with the selected carboxylic acids (SCI scavengers) leading to the formation of a-acyloxyhydroperoxy aldehydes. Ionization conditions were optimized. [M?+?H]+ ions were not formed in ESI; consequently, a-acyloxyhydroperoxy aldehydes were identified as their ammonia adducts for the first time. On the other hand, atmospheric-pressure chemical ionization has led to decomposition of the compounds of interest. Analysis of the mass spectra (MS2 and MS3) of the [M?+?NH4]+ ions allowed recognizing the fragmentation pathways, common for all of the compounds under study. In order to get detailed insights into the fragmentation mechanism, a number of isotopically labeled analogs were also studied. To confirm that the fragmentation mechanism allows predicting the mass spectrum of different a-acyloxyhydroperoxy aldehydes, ozonolysis of a-pinene, a very important secondary organic aerosol precursor, was carried out. Spectra of the two ammonium cationized a-acyloxyhydroperoxy aldehydes prepared with a-pinene, cis-pinonic acid as well as pinic acid were predicted very accurately. Possible applications of the method developed for the analysis of a-acyloxyhydroperoxy aldehydes in SOA samples, as well as other compounds containing hydroperoxide moiety are discussed. Copyright (c) 2013 John Wiley & Sons, Ltd.