Andrade Francisco J, Shelley Jacob T, Wetzel William C, Webb Michael R, Gamez Gerardo, Ray Steven J, Hieftje Gary M
Department of Chemistry, Indiana University, Bloomington, Indiana 47405, USA.
Anal Chem. 2008 Apr 15;80(8):2646-53. doi: 10.1021/ac800156y. Epub 2008 Mar 18.
A novel chemical ionization source for organic mass spectrometry is introduced. This new source uses a glow discharge in the flowing afterglow mode for the generation of excited species and ions. The direct-current gas discharge is operated in helium at atmospheric pressure; typical operating voltages and currents are around 500 V and 25 mA, respectively. The species generated by this atmospheric pressure glow discharge are mixed with ambient air to generate reagent ions (mostly ionized water clusters and NO+), which are then used for the ionization of gaseous organic compounds. A wide variety of substances, both polar and nonpolar, can be ionized. The resulting mass spectra generally show the parent molecular ion (M+ or MH+) with little or no fragmentation. Proton transfer from ionized water clusters has been identified as the main ionization pathway. However, the presence of radical molecular ions (M+) for some compounds indicates that other ionization mechanisms are also involved. The analytical capabilities of this source were evaluated with a time-of-flight mass spectrometer, and preliminary characterization shows very good stability, linearity, and sensitivity. Limits of detection in the single to tens of femtomole range are reported for selected compounds.
介绍了一种用于有机质谱分析的新型化学电离源。这种新源采用流动余辉模式下的辉光放电来产生激发态物种和离子。直流气体放电在大气压下的氦气中进行；典型的工作电压和电流分别约为500 V和25 mA。由这种大气压辉光放电产生的物种与环境空气混合以产生试剂离子（主要是离子化的水簇和NO+），然后用于气态有机化合物的电离。各种各样的物质，无论是极性的还是非极性的，都可以被电离。所得质谱通常显示出母体分子离子（M+或MH+），几乎没有或没有碎片。已确定从离子化水簇进行质子转移是主要的电离途径。然而，某些化合物中存在自由基分子离子（M+）表明还涉及其他电离机制。用飞行时间质谱仪评估了该源的分析能力，初步表征显示出非常好的稳定性、线性和灵敏度。报道了所选化合物在单飞摩尔到数十飞摩尔范围内的检测限。
