Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Effect of water vapour pressure on monoterpene measurements using proton transfer reaction-mass spectrometry (PTR-MS)
AU - Tani, Akira
AU - Hayward, Sean
AU - Hansel, A
AU - Hewitt, C. N.
PY - 2004/12/15
Y1 - 2004/12/15
N2 - The effects of water vapour pressure (WVP) on the fragmentation of seven monoterpene and related C-10 volatile organic compounds (VOCs) in the drift tube of a proton transfer reaction-mass spectrometer (PTR-MS) were investigated. In addition, the combined effects of varying WVP and the ratios of electric field strength to number density of the buffer gas (E/N) were investigated in detail for three of these compounds, the monoterpenes alpha-pinene and sabinene plus the related C-10 VOC p-cymene.Under normal operating conditions (E/N = 124 Td), WVP affected the fragment patterns of all compounds with the exception of beta-pinene and the three oxygenated C-10 VOCs. WVP had a significant effect on the fragment patterns of alpha-pinene and sabinene at the lower E/N ratios (around 80 Td) but had little effect on fragmentation towards the higher E/N ratios used here (similar to142 Td). On the other hand, p-cymene fragmentation was most affected by WVP under normal operating conditions.PTR-MS sensitivity towards the three compounds was also considered under three conditions where reaction was assumed with (1) H3O+ only; (2) H3O+ and H3O+H2O; and (3) H3O+, H3O+H2O and H3O+(H2O)(2). Our results indicate that alpha-pinene and sabinene react not only with H3O+ and H3O+H2O via direct proton transfer but also with H3O+(H2O)-H-()(2) via ligand switching. p-Cymene seems to react only with H3O+ via direct proton transfer and with H3O+H2O via ligand switching. It is speculated that the WVP effect on fragmentation results from the differing abundances of hydrated reagent ions which causes different frequencies of individual reactions to occur, thus, determining how 'soft' the overall reaction is. These results also indicate that under normal conditions, a correction should be made for WVP if the concentration of p-cymene in air samples is to be determined from the single ion signal of either protonated molecular ions or the most dominant fragment ions. (C) 2004 Elsevier B.V. All rights reserved.
AB - The effects of water vapour pressure (WVP) on the fragmentation of seven monoterpene and related C-10 volatile organic compounds (VOCs) in the drift tube of a proton transfer reaction-mass spectrometer (PTR-MS) were investigated. In addition, the combined effects of varying WVP and the ratios of electric field strength to number density of the buffer gas (E/N) were investigated in detail for three of these compounds, the monoterpenes alpha-pinene and sabinene plus the related C-10 VOC p-cymene.Under normal operating conditions (E/N = 124 Td), WVP affected the fragment patterns of all compounds with the exception of beta-pinene and the three oxygenated C-10 VOCs. WVP had a significant effect on the fragment patterns of alpha-pinene and sabinene at the lower E/N ratios (around 80 Td) but had little effect on fragmentation towards the higher E/N ratios used here (similar to142 Td). On the other hand, p-cymene fragmentation was most affected by WVP under normal operating conditions.PTR-MS sensitivity towards the three compounds was also considered under three conditions where reaction was assumed with (1) H3O+ only; (2) H3O+ and H3O+H2O; and (3) H3O+, H3O+H2O and H3O+(H2O)(2). Our results indicate that alpha-pinene and sabinene react not only with H3O+ and H3O+H2O via direct proton transfer but also with H3O+(H2O)-H-()(2) via ligand switching. p-Cymene seems to react only with H3O+ via direct proton transfer and with H3O+H2O via ligand switching. It is speculated that the WVP effect on fragmentation results from the differing abundances of hydrated reagent ions which causes different frequencies of individual reactions to occur, thus, determining how 'soft' the overall reaction is. These results also indicate that under normal conditions, a correction should be made for WVP if the concentration of p-cymene in air samples is to be determined from the single ion signal of either protonated molecular ions or the most dominant fragment ions. (C) 2004 Elsevier B.V. All rights reserved.
KW - water vapour
KW - monoterpene measurements
KW - PTR-MS
KW - volatile organic compounds
KW - fragmentation
KW - VOLATILE ORGANIC-COMPOUNDS
KW - AMBIENT AIR
KW - PPTV LEVELS
KW - ASSOCIATION
U2 - 10.1016/j.ijms.2004.07.020
DO - 10.1016/j.ijms.2004.07.020
M3 - Journal article
VL - 239
SP - 161
EP - 169
JO - International Journal of Mass Spectrometry
JF - International Journal of Mass Spectrometry
SN - 1387-3806
IS - 2-3
ER -