FA-SIFT study of reactions of protonated water and ethanol clusters with α-pinene and linalool in view of their selective detection by CIMS

Chemical ionization by [NO]+ and subsequent collision‐induced dissociation for the selective on‐line detection of monoterpenes and linalool

“…Reactions between protonated ethanol clusters and α‐pinene35 and limonene36 were previously studied by Flowing Afterglow SIFTMS (FASIFTMS) and Atmospheric Pressure Chemical Ionization Mass Spectrometry (APCIMS), respectively, with interesting results relating to the selective detection of these two monoterpenes and linalool. [NO] + ions have been used as reagent ions to distinguish isobaric and even isomeric compounds in a SIFTMS unit29, 35–40 in a drift tube reflectron time‐of‐flight mass spectrometer41, 42 and in a PTRMS instrument 43. The application of [NO] + reagent ions was recently made feasible in a highly sensitive PTRSRIMS instrument,44 from Ionicon Analytik GmbH (Innsbruck, Austria).…”

Modified proton transfer reaction mass spectrometry (PTR‐MS) operating conditions for in vitro and in vivo analysis of wine aroma

“…Proton affinity of the water dimer (H 2 O) 2 (808 ± 6 kJ/mol) is lower than most of VOCs PAs, and therefore (H 2 O) 2 H + participates to proton transfer in conventional PTR‐MS mode. In ethanolic conditions, protonated ethanol dimer could also participate in proton transfer together with ligand switching at collisional rate provided PA of the dimer is not too high . As this PA was not experimentally determined, it has been estimated according to the published method used to estimate the hydrogen bond energy in water dimer using the PA of water dimer .…”

“…8 For linalool, the results presented here were similar to those obtained in a SIFT study where it was demonstrated that the reaction of C 2 H 5 OH 2 + with linalool occurred at the collision rate to give the proton transfer product followed by water elimination and the fragment at m/z 81. 37 In the same study, it was demonstrated that the reaction of the protonated ethanol dimer with linalool occurred at the collision rate, proceeding by proton transfer followed by water elimination (14%) to give the m/z 137 ion, and by ligand switching (77%) followed by water elimination (9%) giving rise to ions at m/z 201 and 183, respectively. 37 Owing to the very low abundance of these ligand switching ions in our PTR-MS experiment ( Table 3) and…”

“…For these linear esters, the main pathway for ion production was clearly proton transfer from the reagent ions (C 2 H 5 OH)H + , their respective proton affinity (a value of 833 kJ/mol has been calculated for the PA of ethyl hexanoate 28 and a measured value of 848-852 kJ/mol reported for ethyl butanoate 26,27 ) being favorable to this only pathway. 39 These new findings concerning esters fragmentation could be rationalized in terms of lower used E/N values and for ethanol-related cluster formation, in terms of temperature used in the drift-tube, set to higher values than in SIFT instruments that generally determined product ion distributions of these reactions 30,37,39,45 and to higher values than previous PTR-MS studies conducted at a drift-tube temperature of 323 K together with higher E/N values. 5 Moreover, it was shown that the relative abundances of proton-bound clusters in PTR-MS were greatly reduced by increasing the chamber temperature above 323 K. 46 Additionally, very low abundances of hydrated ions (M + H 2 O)H + could certainly be also explained by this higher temperature used in the drift-tube (vide supra for the primary ions distribution).…”

“…In ethanolic conditions, protonated ethanol dimer could also participate in proton transfer together with ligand switching at collisional rate provided PA of the dimer is not too high. 37 As this PA was not experimentally determined, it has been estimated according to the published method used to estimate the hydrogen bond energy in water dimer using the PA of water dimer. 36 Hence, the proton affin- of the ethanol dimer was not considered.…”