Methylation of sulfides and thiophenes into methyl sulfonium salts for electrospray ionization (ESI) mass spectrometry analysis has been a widely used approach for molecular characterization of sulfur-containing compounds in fossil fuels. In this study, we found a series of artifacts in the methylation products of crude oils, which could lead to incorrect assignment of sulfur compounds, severe ionization suppression of S₁ species with a high double bond equivalent value, and O_xS_x species with low abundance. The terminal products from the Friedel–Craft methylation of toluene and its methyl homologues were identified as 1,1,2,3,4,5,6-heptamethylbenzenonium, which showed high abundance in the positive-ion ESI mass spectrum. These compounds associate with Ag⁺, leading to the formation of abundant Ag-cationized monomer and homo- and hetero-Ag-cationized dimer complexes. In-source high-energy collisional dissociation (HCD) of the homo- and hetero-Ag-cationized dimer complexes [M₁ + Ag + M₁]⁺ and [M₁ + Ag + M₂]⁺ yielded the monomer complexes [M₁ + Ag]⁺, which further fragmented to yield the molecular ion [M₁]⁺. The abundant Ag-cationized complexes seriously interfered with the identification of sulfur compounds. Feasible suggestions are made to eliminate the interference by Ag-cationized complexes.

中文翻译：

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石油中硫化合物甲基化过程中的伪像鉴定

硫化物和噻吩甲基化成甲基analysis盐用于电喷雾电离（ESI）质谱分析，已广泛用于化石燃料中含硫化合物的分子表征。在这项研究中，我们发现了一系列原油中的甲基化产物的工件，这可能导致硫化合物的不正确分配，S的严重电离抑制_1个具有高双键当量值物种，和O _X小号_X物种低丰度。甲苯的Friedel-Craft甲基化及其甲基同系物的最终产物被鉴定为1,1,2,3,4,5,6-七甲基苯甲铵，在正离子ESI质谱图中显示出高丰度。这些化合物与银结合⁺，导致形成大量的Ag阳离子化单体以及均Ag和杂Ag阳离子化的二聚体复合物。均-和杂-Ag阳离子化的二聚体[M ₁ + Ag + M ₁ ] ⁺和[M ₁ + Ag + M ₂ ] ⁺的源内高能碰撞解离（HCD）得到单体复合物[M ₁ + Ag] ⁺，其进一步裂解生成分子离子[M ₁ ] ⁺。大量的银阳离子化的配合物严重干扰了硫化合物的鉴定。提出了可行的建议来消除Ag阳离子化配合物的干扰。