Oktem Berk, Tolocka Michael P, Johnston Murray V
Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA.
Anal Chem. 2004 Jan 15;76(2):253-61. doi: 10.1021/ac0350559.
A new method, photoionization aerosol mass spectrometry (PIAMS), is described for real-time analysis of organic components in airborne particles below approximately 300 nm in diameter. Particles are focused through an aerodynamic lens assembly into the mass spectrometer where they are collected on a probe in the source region. After a sufficient amount of sample has been collected, the probe is irradiated with a pulsed infrared laser beam to vaporize organic components, which are then softly ionized with coherent vacuum ultraviolet radiation at 118 nm (10.5 eV). Since the photon energy is close to the ionization energies of most organic compounds, fragmentation is minimized. Both aliphatic and aromatic compounds of atmospheric relevance are detected and quantified in the low- to midpicogram range. The photoionization signal intensity increases linearly with the amount of material sampled and is independent of particle size. The fragmentation induced by laser desorption is greater than that observed with thermal vaporization, suggesting that the internal energy imparted by the former is greater. Although some molecular fragmentation is observed, mass spectra from common sources of ambient organic aerosol are distinguishable and consistent with previous off-line measurements by gas chromatography/mass spectrometry. These results illustrate the potential of PIAMS for molecular characterization of organic aerosols in ambient and smog chamber measurements.
本文介绍了一种新方法——光电离气溶胶质谱法（PIAMS），用于实时分析直径约300 nm以下空气中颗粒物中的有机成分。颗粒物通过气动透镜组件聚焦进入质谱仪，在源区被收集在一个探头上。在收集到足够量的样品后，用脉冲红外激光束照射探头以汽化有机成分，然后用118 nm（10.5 eV）的相干真空紫外辐射将其软电离。由于光子能量接近大多数有机化合物的电离能，碎片形成被最小化。大气相关的脂肪族和芳香族化合物均能在低至中皮克范围内被检测和定量。光电离信号强度随采样物质的量呈线性增加，且与颗粒大小无关。激光解吸引起的碎片化大于热汽化时观察到的碎片化，这表明前者赋予的内能更大。尽管观察到了一些分子碎片化，但来自环境有机气溶胶常见来源的质谱是可区分的，并且与之前通过气相色谱/质谱进行的离线测量结果一致。这些结果说明了PIAMS在环境和烟雾箱测量中对有机气溶胶进行分子表征的潜力。
