COLLISION-INDUCED DISSOCIATION STUDIES OF PROTONATED ALCOHOL AND ALCOHOL-WATER CLUSTERS BY ATMOSPHERIC-PRESSURE IONIZATION TANDEM MASS-SPECTROMETRY .2. ETHANOL, PROPANOL AND BUTANOL

Protonated clusters of alcohols, (ROH)(n)H+, and alcohol-water heteroc lusters, (ROH)n(H2O)mH+, where R = C2H5, n-C3H7, iso-C3H7, n-C4H9, iso -C4H9, sec-C4H9 and tert-C4H9, were formed in an atmospheric pressure ionization (API) corona discharge source, through proton transfer and displacement ion-molecule reactions with (H2O)nH+. The cluster ions we re then subjected to collision induced dissociation (CID) in a tandem mass spectrometer (API-MS-MS). Stabilities of the clusters were examin ed through cluster size distribution analysis and CID reaction channel s. The results gave insights about the structure and energetics of the clusters. The heteroclusters demonstrated a strong preference for wat er elimination over alcohol elimination, indicating that the alcohol m oiety was the favored protonation site. The CID results indicated that in the heteroclusters water ligands were near the periphery of a chai n, along which water and alcohol molecules were hydrogen bonded. This structural model could rationalize product ion formation through a sin gle hydrogen bond cleavage for mild CID conditions and through breakin g of two hydrogen bonds or a single bond after proton migration along the chain under enhanced fragmentation conditions. CID of protonated a lcohols showed differences in the cleavage of C-O bonds vs. O-H+ bonds , as well as variance in product ion distributions in the alcohols.