Pack B W, Broekaert J A, Guzowski J P, Poehlman J, Hieftje G M
Department of Chemistry, Indiana University, Bloomington 47405, USA.
Anal Chem. 1998 Sep 15;70(18):3957-63. doi: 10.1021/ac970534r.
A helium microwave plasma torch (MPT) was coupled to time-of-flight mass spectrometry (TOFMS) for the detection of halogenated hydrocarbons separated by capillary gas chromatography (GC). The GC-MPT-TOFMS system offered excellent stability over the course of the experiments and avoided mass spectral peak distortions caused by spectral skew. In the initial studies, empirical formulas based on the halogen-to-carbon ratio were predicted utilizing a flow cell apparatus. The MPT proved to be very robust and could handle large amounts of organic vapor. Results from this study indicate that, for both aromatic and aliphatic halogenated hydrocarbons, the ratios of carbon to chlorine signals correlate well (r = 0.994) with the ones expected from their chemical composition. This study was later extended to include chromatographic separation. For a series of homologous aliphatic halogenated hydrocarbons, a correlation coefficient of 0.999 was obtained for both peak heights and peak areas obtained from a single chromatogram. A novel Nichrome wire-heated transfer line was developed to ensure that the capillary column was heated efficiently from the GC oven to the MPT and then through the length of the MPT up to the microwave plasma itself. No appreciable peak broadening and no detectable memory effects were associated with the heated transfer line. The GC-MPT-TOFMS system offered equal sensitivity for I, Br, and Cl. Absolute detection limits for the halogenated hydrocarbons ranged from 160 to 330 fg, constituting an improvement by a factor of 5-35 over earlier results obtained with MIPs supported in a TM010 cavity and combined with quadrupole-based mass spectrometry. In addition, the effect of molecular gases on the MPT performance was investigated. Up to about 1% (v/v) of either oxygen or hydrogen in the central channel helium flow attenuated the signal levels for both carbon and chlorine, with the larger loss seen in the chlorine signal.
将氦微波等离子体炬（MPT）与飞行时间质谱仪（TOFMS）联用，用于检测通过毛细管气相色谱（GC）分离的卤代烃。在整个实验过程中，GC-MPT-TOFMS系统具有出色的稳定性，避免了由光谱偏斜引起的质谱峰畸变。在最初的研究中，利用流通池装置预测了基于卤素与碳比率的经验公式。事实证明，MPT非常耐用，能够处理大量有机蒸气。该研究结果表明，对于芳香族和脂肪族卤代烃，碳与氯信号的比率与根据其化学组成预期的比率相关性良好（r = 0.994）。该研究后来扩展到包括色谱分离。对于一系列同系脂肪族卤代烃，从单个色谱图获得的峰高和峰面积的相关系数均为0.999。开发了一种新型镍铬合金丝加热传输线，以确保毛细管柱从气相色谱炉有效地加热到MPT，然后通过MPT的长度直至微波等离子体本身。加热传输线没有明显的峰展宽，也没有可检测到的记忆效应。GC-MPT-TOFMS系统对碘、溴和氯具有相同的灵敏度。卤代烃的绝对检测限在160至330 fg之间，比早期在TM010腔中支持的MIP与基于四极杆的质谱联用所获得的结果提高了5至35倍。此外，还研究了分子气体对MPT性能的影响。在中心通道氦气流中，氧气或氢气的含量高达约1%（v/v）时，会使碳和氯的信号水平衰减，氯信号的损失更大。
