Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg-University of Mainz, Duesbergweg 10-14, 55128 Mainz.
Anal Chem. 2012 Feb 7;84(3):1439-45. doi: 10.1021/ac202527a. Epub 2012 Jan 19.
Here we present a new application of a time-of-flight aerosol mass spectrometer (TOF-AMS) for the measurement of atmospheric trace gases in real-time. Usually, TOF-AMS instruments are not sensitive to gas-phase species due to the aerodynamic particle focusing inlet system which reduces the gas phase species by a factor of about 10(7) relative to the particle phase. This efficient removal of the gas phase and the resulting high relative enrichment of particles is one reason for the very high sensitivity of TOF-AMS instruments for particle phase compounds (detection limits in the sub-μg/m(3)-range for online measurements with 1 min integration time), which allows application of the instruments even under clean atmospheric conditions. Here we use artificially generated particles as sampling probes to transfer selected atmospheric trace gases into the particle phase before entering the AMS (gaseous compound trapping in artificially generated particles-AMS, GTRAP-AMS). The sampling probe particles are mixed with the gaseous analytes upstream of the TOF-AMS in a 0.5 L flow tube. As an exemplary application of the method, the measurement of trace levels of gaseous molecular iodine is demonstrated. α-Cyclodextrin (α-CD/NH(4)Br) particles are used as selective sampling probes to transfer molecular iodine into the AMS. A detection limit in the subparts-per-billion (sub-ppb) range was achieved. The method was compared to a recently developed off-line method that combines denuder sampling of gaseous I(2) and gas chromatography/mass spectrometry (GC/MS) analysis. To demonstrate the usability of the method, temporally resolved I(2) emission profiles from a brown algae species (Laminaria saccharina) under exposure of ambient ozone levels were investigated. Total I(2) release rates of 36.5 pmol min(-1) grams fresh weight (gFW)(-1) at 100 pbb O(3) and 33.4 pmol min(-1) gFW(-1) at 50 ppb O(3) were obtained within the first hour of ozone exposure.
这里我们提出了一种飞行时间气溶胶质谱仪（TOF-AMS）的新应用，用于实时测量大气痕量气体。通常，由于空气动力学粒子聚焦入口系统，TOF-AMS 仪器对气相物种不敏感，该系统将气相物种相对于粒子相减少约 10(7)倍。这种高效去除气相和由此产生的粒子相的高相对富集是 TOF-AMS 仪器对粒子相化合物非常高灵敏度的原因之一（在线测量时，使用 1 分钟积分时间，检测限为亚微克/立方米范围内），即使在清洁的大气条件下，也可以应用这些仪器。在这里，我们使用人工生成的粒子作为采样探针，在进入 AMS 之前将选定的大气痕量气体转移到粒子相中（在人工生成的粒子中捕获气态化合物-AMS，GTRAP-AMS）。采样探针粒子在 0.5 L 流量管中与气态分析物在 TOF-AMS 上游混合。作为该方法的示例应用，演示了痕量气态分子碘的测量。α-环糊精（α-CD/NH(4)Br）粒子用作选择性采样探针，将分子碘转移到 AMS 中。实现了亚部分-每十亿（亚 ppb）范围内的检测限。该方法与最近开发的离线方法进行了比较，该方法结合了气态 I(2)的除尘器采样和气相色谱/质谱（GC/MS）分析。为了证明该方法的可用性，研究了在暴露于环境臭氧水平下，褐藻（Laminaria saccharina）的 I(2)排放轮廓的时间分辨。在臭氧暴露的第一个小时内，在 100 pbb O(3)下获得了 36.5 pmol min(-1)克鲜重（gFW）(-1)的总 I(2)释放速率，在 50 ppb O(3)下获得了 33.4 pmol min(-1) gFW(-1)的总 I(2)释放速率。
