RATIONALE Monoterpene hydrocarbons play an important role in the formation of secondary aerosol particles and in atmospheric chemistry. Thus, there is a demand to measure their individual concentrations in situ in real time. Currently, only the total concentration of monoterpenes C10 H16 can be determined by chemical ionization mass spectrometry techniques using reagent ions H3 O+ , NO+ and (C6 H6 )n +• without gas chromatographic separation. METHODS The styrene cation C8 H8 +• was investigated as a reagent for chemical ionization of monoterpenes. The modified selected ion flow drift tube, SIFDT, technique was used to characterize the differences in product ion distributions between α-phellandrene, α-pinene, γ-terpinene, β-pinene, ocimene, sabinene, 3-carene, (R)-limonene, camphene and myrcene. RESULTS The monoterpene molecular cation C10 H16 +• is the main product (about 90%) for all isomers except (R)-limonene and camphene with an efficient channel of C8 H8 +• C10 H16 adduct formation and γ-terpinene with unexpectedly significant product ions at m/z 134 and 135 corresponding to losses of H2 and H. CONCLUSIONS Utilization of the styrene cation for the ionization of monoterpenes is beneficial due to the very low fragmentation of the product ions. Specific association product ions for camphene and (R)-limonene and fragment product ions for γ-terpinene allow them to be distinguished from other isomers that produce mostly the molecular cation.

中文翻译：

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用于单萜碳氢化合物化学电离质谱分析的苯乙烯自由基阳离子。

理由单萜碳氢化合物在次级气溶胶颗粒的形成和大气化学中起着重要作用。因此，需要实时地原位测量它们的单独浓度。目前，仅单萜C10 H16的总浓度可以通过化学电离质谱技术使用试剂离子H3 O +，NO +和（C6 H6）n +•进行测定，而无需进行气相色谱分离。方法研究了苯乙烯阳离子C8 H8 +•作为单萜化学电离的试剂。改良的选择离子流漂移管SIFDT技术用于表征α-水芹烯，α-pine烯，γ-萜品烯，β-ne烯，罗勒烯，sa烯，3-烯，（R）-之间的产物离子分布差异柠檬烯，camp烯和月桂烯。结果单萜分子阳离子C10 H16 +•是所有异构体的主要产物（约90％），但（R）-柠檬烯和camp烯具有有效的C8 H8 +•C10 H16加合物形成通道和γ-萜品烯，且出乎意料的重要产物离子在m / z 134和135对应于H2和H的损失。结论由于产物离子的碎裂非常低，因此利用苯乙烯阳离子进行单萜的离子化是有益的。camp烯和（R）-柠檬烯的特定缔合产物离子和γ-萜品烯的碎片产物离子可将它们与主要产生分子阳离子的其他异构体区分开。