Brocks Jochen J, Hope Janet M
Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia
Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia.
J Chromatogr Sci. 2014 Jul;52(6):471-5. doi: 10.1093/chromsci/bmt068. Epub 2013 Jun 18.
The injection of analytes into a gas chromatography-mass spectrometry (GC-MS) system using dichloromethane (DCM) as solvent led to gradual deterioration of chromatographic signals, with significant tailing and loss of sensitivity for C17+ hydrocarbons. The injector, gas chromatograph and transfer line were excluded as causes. Normal peak shape could only be restored by the insertion of a cleaned MS ion source. To elucidate potential surficial contaminants, the ion source was heated from 260 to 320°C, leading to the release of increasing concentrations of ferrous chloride [FeCl2(g)]. The ferrous chloride probably formed through the decomposition of DCM on metal surfaces in the ion source. We posit that the tailing was caused by the adsorption of analytes to sub-µm layers of FeCl2 at crystal defect sites in the metal, followed by the slow release of molecules back into the gas phase. There are at least two other cases in the literature in which tailing is specifically associated with the use of halogenated solvents. However, it is possible that the problem is relatively common, albeit rarely diagnosed and reported. The tailing of chromatographic peaks caused by the formation of ferrous chloride in the mass spectrometer can be diagnosed by scanning the MS background signal for the diagnostic isotopic pattern of FeCl2(+). The problem is easily solved by cleaning the MS ion source and avoiding halogenated solvents.
使用二氯甲烷（DCM）作为溶剂将分析物注入气相色谱-质谱联用（GC-MS）系统会导致色谱信号逐渐变差，C17+碳氢化合物出现明显拖尾且灵敏度降低。已排除进样器、气相色谱仪和传输线是造成此问题的原因。只有插入清洁后的质谱离子源才能恢复正常的峰形。为了阐明潜在的表面污染物，将离子源从260°C加热到320°C，导致释放出浓度不断增加的氯化亚铁[FeCl2(g)]。氯化亚铁可能是由离子源中金属表面的DCM分解形成的。我们推测拖尾是由于分析物吸附到金属晶体缺陷部位亚微米层的FeCl2上，随后分子缓慢释放回气相中所致。文献中至少还有另外两个案例，其中拖尾现象与卤代溶剂的使用有特定关联。然而，这个问题可能相对普遍，尽管很少被诊断和报道。质谱仪中因形成氯化亚铁导致的色谱峰拖尾可通过扫描MS背景信号以查找FeCl2(+)的诊断同位素模式来诊断。通过清洁质谱离子源并避免使用卤代溶剂，这个问题很容易解决。
