Wang Shunyang, Valdiviez Luis, Ye Honglian, Fiehn Oliver
Department of Chemistry, University of California, Davis, CA 95616, USA.
West Coast Metabolomics Center, University of California, Davis, CA 95616, USA.
Metabolites. 2023 Aug 19;13(8):962. doi: 10.3390/metabo13080962.
Gas chromatography-mass spectrometry (GC-MS) usually employs hard electron ionization, leading to extensive fragmentations that are suitable to identify compounds based on library matches. However, such spectra are less useful to structurally characterize unknown compounds that are absent from libraries, due to the lack of readily recognizable molecular ion species. We tested methane chemical ionization on 369 trimethylsilylated (TMS) derivatized metabolites using a quadrupole time-of-flight detector (QTOF). We developed an algorithm to automatically detect molecular ion species and tested SIRIUS software on how accurate the determination of molecular formulas was. The automatic workflow correctly recognized 289 (84%) of all 345 detected derivatized standards. Specifically, strong [M - CH] fragments were observed in 290 of 345 derivatized chemicals, which enabled the automatic recognition of molecular adduct patterns. Using Sirius software, correct elemental formulas were retrieved in 87% of cases within the top three hits. When investigating the cases for which the automatic pattern analysis failed, we found that several metabolites showed a previously unknown [M + TMS] adduct formed by rearrangement. Methane chemical ionization with GC-QTOF mass spectrometry is a suitable avenue to identify molecular formulas for abundant unknown peaks.
气相色谱 - 质谱联用（GC - MS）通常采用硬电子电离，会导致广泛的碎片化，这适合基于谱库匹配来鉴定化合物。然而，由于缺乏易于识别的分子离子种类，对于谱库中不存在的未知化合物进行结构表征时，这样的质谱图用处较小。我们使用四极杆飞行时间检测器（QTOF）对369种三甲基硅烷基化（TMS）衍生代谢物进行了甲烷化学电离测试。我们开发了一种算法来自动检测分子离子种类，并测试了SIRIUS软件在确定分子式的准确性方面的表现。自动工作流程正确识别了所有345种检测到的衍生标准物中的289种（84%）。具体而言，在345种衍生化学品中的290种中观察到了强的[M - CH]碎片，这使得能够自动识别分子加合物模式。使用Sirius软件，在前三个命中结果中，87%的情况下检索到了正确的元素分子式。在研究自动模式分析失败的情况时，我们发现几种代谢物显示出通过重排形成的先前未知的[M + TMS]加合物。气相色谱 - QTOF质谱联用的甲烷化学电离是确定大量未知峰分子式的合适方法。
