Department of Chemistry, Key Laboratory for Atomic and Molecular Nanosciences of Education Ministry, Tsinghua University, 100084 Beijing, PR China.
Rapid Commun Mass Spectrom. 2010 Mar;24(6):742-8. doi: 10.1002/rcm.4444.
A new low-temperature plasma (LTP), based on dielectric barrier discharge (DBD), has been developed as an alternative ionization source for ambient mass spectrometry. For organic samples, the source is able to produce two different fragmentation patterns which are selectable by an electrical switch. The two source modes are different only in the second electrodes: in configuration (A), bar-plate and in configuration (B), coaxial bar-cylinder shapes are used. A disposable graphite probe is used as the first electrode, the same in both configurations, and a copper foil is used as the second electrode. The ionization source is applicable to gas and liquid samples, without any change being necessary in its design. Under optimal conditions, to take ethylbenzene as an example, a detection limit of less than 25 ng was obtained and a relative standard deviation (RSD) of 13.36% has been demonstrated for 50 ng of ethylbenzene (n = 11). We have found several interesting differences in the mass spectra of the tested volatile organic compounds (VOCs) in the two modes, which might be applicable in identification studies. We have investigated the effect of variation of the first electrode material and the second electrode length in mode B. Moreover, in this design the graphite electrode is capable of acting as a sample adsorbent, which is a new sampling method for LTP mass spectrometry (MS). This capability was investigated by adsorption of the selected VOCs onto the surface of the graphite electrode in a headspace solid-phase microextraction (SPME) system, and direct desorption and ionization of the samples by LTPMS.
一种新的低温等离子体（LTP），基于介质阻挡放电（DBD），已被开发为环境质谱分析的替代电离源。对于有机样品，该源能够产生两种不同的碎片模式，可以通过电开关选择。两种源模式仅在第二电极上有所不同：在配置（A）中，使用棒-板，而在配置（B）中，使用同轴棒-圆柱形状。一次性石墨探针用作第一电极，两种配置中均相同，而铜箔用作第二电极。该电离源适用于气体和液体样品，无需对其设计进行任何更改。在最佳条件下，以乙苯为例，得到的检测限低于 25ng，并且对于 50ng 的乙苯（n=11），相对标准偏差（RSD）为 13.36%。我们在两种模式下测试的挥发性有机化合物（VOCs）的质谱中发现了一些有趣的差异，这可能适用于鉴定研究。我们研究了第一电极材料和第二电极长度在模式 B 中的变化的影响。此外，在这种设计中，石墨电极能够作为样品吸附剂，这是 LTP 质谱（MS）的一种新的采样方法。通过在顶空固相微萃取（SPME）系统中将选定的 VOCs 吸附到石墨电极表面上，以及通过 LTPMS 直接解吸和离子化来研究这种能力。
