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首页> 外文期刊>Journal of mass spectrometry: JMS >GC-MS with photoionization of cold molecules in supersonic molecular beams-Approaching the softest ionization method
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GC-MS with photoionization of cold molecules in supersonic molecular beams-Approaching the softest ionization method

机译：GC-MS具有在超声分子束中的冷分子的光离子 - 接近最柔软的电离方法

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A new type of photoionization ion source was developed for the ionization of cold molecules in supersonic molecular beams (named Cold PI). The system was based on a GC-MS with supersonic molecular beams and its fly-through EI of cold molecules ion source (Cold EI) plus quadrupole mass analyzer. A continuously operated deuterium VUV photoionization lamp was added and placed above and between the supersonic nozzle and skimmer whereas the Cold EI ion source served only as a portion of the ion transfer ion optics. The supersonic nozzle and skimmer were voltage biased and the VUV light crossed the supersonic expansion about 10 mm from the nozzle. We obtained over three orders of magnitude enhancement in the relative abundance of the molecular ion of squalane in Cold PI versus in photoionization of this compound as a thermal compound. Accordingly, we also proved that standard photoionization is not as soft ionization method as previously perceived for large compounds. We found that Cold PI is as soft as and possibly softer than field ionization; thus, it could be the softest known ionization method. The ionization yield was about 200-300 times weaker than with Cold EI yet our limit of detection was about 200 femtogram in SIM mode for cholesterol and pyrene which is reasonable. Practically, all hydrocarbons gave only molecular ions with rather uniform response whereas alcohols gave some molecular ions plus major fragment ions particularly with a loss of water (similarly to field ionization). We tested Cold PI in the GC-MS analysis of diesel fuels and analyzed the time averaged data for group type information. We also found that we can analyze the diesel fuels by fast under 20-s flow injection analysis in which the generated averaged mass spectrum of molecular ions only could serve for the characterization of fuels.
机译：开发了一种新型的光离子源，用于超声波分子束中的冷分子电离（命名为冷PI）。该系统基于具有超声波分子束的GC-MS及其飞越冷分子离子源（冷EI）加上四极杆质量分析仪。加入连续操作的氘VUV光离子灯并放置在超音速喷嘴和撇油之间，而冷EI离子源仅作为离子转移离子光学器件的一部分。超音速喷嘴和撇渣器是电压偏置，VUV光线距离喷嘴约10mm的超音速膨胀。我们在冷PI与该化合物的光相消隐的光PI与热化合物中的光学离子中的分子离子的相对丰度中获得了三个数量级增强。因此，我们还证明标准光离子不像以前所吸引的大型化合物那样软离子化方法。我们发现冷PI与现场电离一样柔软，可能更柔软;因此，它可以是最柔软的已知电离方法。与冷EI较弱的电离产率约为200-300倍，但我们的检测极限是胆固醇和芘的SIM模式中约200个模拟。实际上，所有烃都只有具有相当均匀的响应的分子离子，而醇则给出一些分子离子加上主要碎片离子，特别是损失水（与现场电离类似）。我们在柴油燃料的GC-MS分析中测试了冷PI，分析了组类型信息的时间平均数据。我们还发现，我们可以通过快速分析柴油燃料，其20-S流注入分析，其中分子离子的产生的平均质谱可以用于燃料的表征。

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