Selective measurements of isoprene and 2-methyl-3-buten-2-ol based on NO+ ionization mass spectrometry
Selective measurements of isoprene and 2-methyl-3-buten-2-ol based on NO+ ionization mass spectrometry
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DOI：
10.5194/acp-12-11877-2012
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发表时间：
2012-01-01
影响因子：
6.3
通讯作者：
Jud, W.
中科院分区：
文献类型：
--
作者：
Karl, T.;Hansel, A.;Jud, W.
生物来源的VOC排放通常以2-甲基-1，3-丁二烯(异戊二烯)和2-甲基-3-丁烯-2-醇(232MBO)为主。在这里，我们探索了在配备SRI单元的传统PTR-MS中使用NO+作为初级离子来选择性区分这些物种的可能性。采用常规的PTR-TOF-MS，在实验室和现场实验中使用了高纯度的NO+(>；90%)作为初级离子。异戊二烯通过电荷转移被电离，产生主要产物离子C5H8+(>；99%)(例如Spanel和Smith，1998)。232 MBO经历氢氧化物离子转移反应，产生主要产物离子通道C5H9+(>；95%)(例如，Amelynck等人，2005年)。我们发现，在标准操作条件下，这两种化合物都是电离的，碎片很少(<；5%)。典型的灵敏度分别为11.1+/-0.1(异戊二烯)和12.9+/-0.1(232MBO)NCPs ppbv(-1)，相当于对10个S积分时间的检测下限分别为18和15 PPTV。碰撞能量越高，灵敏度越低。校准实验表明，湿度依赖性很小。我们在科罗拉多州的一个以黄皮松为主的田野现场测试了这一设置，黄皮松是一种释放MBO的植物。我们的测量证实232 MBO是该地点的主要生物来源VOC，典型的日间平均浓度在0.2-1.4ppbv之间。该方法能够在现场(90-250 ppt)检测到痕量异戊二烯的存在，而不会受到232 MBO的任何干扰，这在H3O+电离化学中是不可行的，目前这对其他分析技术(例如，气相色谱方法)也是一个挑战。
Biogenic VOC emissions are often dominated by 2-methyl-1,3-butadiene (isoprene) and 2-methyl-3-buten-2-ol (232 MBO). Here we explore the possibility to selectively distinguish these species using NO+ as a primary ion in a conventional PTR-MS equipped with an SRI unit. High purity of NO+ (> 90 %) as a primary ion was utilized in laboratory and field experiments using a conventional PTR-TOF-MS. Isoprene is ionized via charge transfer leading to the major product ion C5H8+ (> 99 %) (e. g. Spanel and Smith, 1998). 232 MBO undergoes a hydroxide ion transfer reaction resulting in the major product ion channel C5H9+ (> 95 %) (e. g. Amelynck et al., 2005). We show that both compounds are ionized with little fragmentation (< 5 %) under standard operating conditions. Typical sensitivities of 11.1 +/- 0.1 (isoprene) and 12.9 +/- 0.1 (232 MBO) ncps ppbv(-1) were achieved, which correspond to limit of detections of 18 and 15 pptv respectively for a 10 s integration time. Sensitivities decreased at higher collisional energies. Calibration experiments showed little humidity dependence. We tested the setup at a field site in Colorado dominated by ponderosa pine, a 232 MBO emitting plant species. Our measurements confirm 232 MBO as the dominant biogenic VOC at this site, exhibiting typical average daytime concentrations between 0.2-1.4 ppbv. The method is able to detect the presence of trace levels of isoprene at this field site (90-250 ppt) without any interference from 232 MBO, which would not be feasible using H3O+ ionization chemistry, and which currently also remains a challenge for other analytical techniques (e. g. gas chromatographic methods).