Institute of Food Chemistry (170b), University of Hohenheim, Garbenstrasse 28, D-70599 Stuttgart, Germany.
Anal Chem. 2010 Dec 1;82(23):9835-42. doi: 10.1021/ac102134x. Epub 2010 Nov 4.
Nontarget analysis and identification of unknown polyhalogenated compounds is important in acquiring a thorough picture of the present pollution status as well as for identifying emerging environmental problems. Such analyses usually require the application of electron ionization mass spectrometry because the resulting mass spectra frequently allow for compound identification. When quadrupoles are used as mass separators, the full scan technique often suffers from low sensitivity along with nonspecificity for polyhalogenated trace compounds which often result in interference by matrix compounds. We have developed a novel nontarget gas chromatography/electron ionization-mass spectrometry-selected ion monitoring (GC/EI-MS-SIM) method that overcomes these sensitivity and selectivity issues. Our method is based on the fact that the molecular ions and isotope patterns of polyhalogenated compounds involve the most relevant primary information with regard to the structure of polyhalogenated compounds. Additionally, the retention times of polyhalogenated compounds generally increase with increasing molecular weight. The retention time range of polyhalogenated compounds was divided in three partly overlapping segments of 112 u (segment A: m/z 300-412; segment B: m/z 350-462; segment C: m/z 450-562) that were screened in eight GC runs consisting of 15 consecutive SIM ions. This method was tested with a passive water sampler extract known to contain over 30 polyhalogenated compounds according to the sensitive analysis by GC/electron capture negative ion (ECNI)-MS. While none of these polyhalogenated compounds could be detected by GC/EI-MS in full scan mode, our nontarget GC/EI-MS-SIM method allowed for the detection of 38 polyhalogenated compounds. Only seven could be identified by means of reference standards while more than 15 of the unknowns could be traced back to at least the class of compounds based on the mass spectrometric data from the nontarget SIM runs. All compounds identified originated from halogenated natural products. The nontarget GC/EI-MS-SIM method combines the high sensitivity obtainable with quadrupole systems for trace analysis with the structural information essential for the identification of unknown pollutants.
非目标分析和未知多卤代化合物的鉴定对于全面了解当前污染状况以及识别新出现的环境问题非常重要。此类分析通常需要应用电子电离质谱，因为所得质谱通常允许进行化合物鉴定。当四极杆用作质量分离器时，全扫描技术通常存在灵敏度低和对多卤代痕量化合物特异性差的问题，这往往会导致基质化合物的干扰。我们开发了一种新颖的非目标气相色谱/电子电离-质谱-选择离子监测（GC/EI-MS-SIM）方法，该方法克服了这些灵敏度和选择性问题。我们的方法基于以下事实，即多卤代化合物的分子离子和同位素模式涉及与多卤代化合物结构最相关的主要信息。此外，多卤代化合物的保留时间通常随分子量的增加而增加。多卤代化合物的保留时间范围分为三个部分重叠的 112 u 段（段 A：m/z 300-412；段 B：m/z 350-462；段 C：m/z 450-562），在由 15 个连续 SIM 离子组成的 8 次 GC 运行中进行筛选。该方法使用已知含有 30 多种多卤代化合物的被动水采样器提取物进行了测试，根据 GC/电子俘获负离子（ECNI）-MS 的灵敏分析。虽然在全扫描模式下，GC/EI-MS 无法检测到这些多卤代化合物中的任何一种，但我们的非目标 GC/EI-MS-SIM 方法允许检测到 38 种多卤代化合物。只有七种可以通过参比标准来识别，而超过 15 种未知物可以根据非目标 SIM 运行的质谱数据追溯到至少化合物类别。所有鉴定的化合物均源自卤化天然产物。非目标 GC/EI-MS-SIM 方法将痕量分析中四极杆系统的高灵敏度与识别未知污染物所需的结构信息相结合。
