RATIONALE Gas chromatography coupled to electron ionization mass spectrometry (GC/EI-MS) is used for routine screening of anabolic steroids in many laboratories after the conversion of polar groups into trimethylsilyl (TMS) derivatives. The aim of this work is to elucidate the origin and formation of common and subclass-specific fragments in the mass spectra of TMS-derivatized steroids. Especially in the context of metabolite identification or analysis of designer drugs, isotopic labelling is helpful to better understand fragment ion generation, identify unknown compounds and update established screening methods. METHODS Stable isotope labelling procedures for the introduction of [2 H9 ]-TMS or 18 O were established to generate perdeuterotrimethylsilylated, mixed deuterated and 18 O-labelled derivatives for 13 different hydroxy steroids. Fragmentation proposals were substantiated by comparison of the abundances of isotopically labelled and unlabelled fragment ions in unit mass resolution GC/MS. Specific fragmentations were also investigated by high-resolution MS (GC/quadrupole time-of-flight MS, GC/QTOFMS). RESULTS Methyl radical cleavage occurs primarily from the TMS groups in saturated androstanes and from the steroid nucleus in the case of enol-TMS of oxo or α,β-unsaturated steroid ketones. Loss of trimethylsilanol (TMSOH) is dependent on steric factors, degree of saturation of the steroid backbone and the availability of a hydrogen atom and TMSO group in the 1,3-diaxial position. For the formation of the [M - 105]+ fragment ion, methyl radical cleavage predominates from the angular methyl groups in position C-18 or C-19 and is independent of the site of TMSOH loss. The common [M - 15 - 76]+ fragment ion was found in low abundance and identified as [M - CH3 - (CH3 )2 SiH - OH]+ . For the different steroid subclasses further diagnostic fragment ions were discussed and structure proposals postulated. CONCLUSIONS Stable isotope labelling of oxo groups as well as derivatization with deuterated TMS groups enables the detection of structure-related fragment ion generation in unit mass resolution GC/EI-MS. This may in turn allow us to propose isomeric assignments that are otherwise almost impossible using MS only.

中文翻译：

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使用气相色谱/电子电离低分辨率质谱法对同位素标记的羟基类固醇进行质谱碎片分析：一种实用方法。

RATIONALE在许多实验室中，将极性基团转化为三甲基甲硅烷基（TMS）衍生物后，气相色谱与电子电离质谱（GC / EI-MS）联用于常规合成代谢类固醇的筛选。这项工作的目的是阐明TMS衍生类固醇的质谱中常见和亚类特异性片段的起源和形成。尤其是在代谢物鉴定或设计药物分析的背景下，同位素标记有助于更好地理解碎片离子的产生，鉴定未知化合物并更新已建立的筛选方法。方法建立了用于引入[2 H9] -TMS或18 O的稳定同位素标记程序，以生成13种不同羟基类固醇的全氘三甲基甲硅烷基化，混合氘代和18 O标记的衍生物。通过比较单位质量分辨率GC / MS中同位素标记和未标记的碎片离子的丰度，可以实现碎片建议。还通过高分辨率质谱仪（GC /四极杆飞行时间质谱仪，GC / QTOFMS）研究了特定的碎片。结果甲基自由基的裂解主要发生在饱和雄烷中的TMS基团中，对于oxo的烯醇-TMS或α，β-不饱和类固醇酮，则发生在类固醇核中。三甲基硅烷醇（TMSOH）的损失取决于空间因素，类固醇主链的饱和度以及在1,3-双轴位的氢原子和TMSO基团的可用性。对于[M-105] +碎片离子的形成，甲基自由基的切割主要来自位置C-18或C-19的有角甲基，并且与TMSOH的损失位置无关。常见的[M-15-76] +碎片离子含量低，被鉴定为[M-CH3-（CH3）2 SiH-OH] +。对于不同的类固醇亚类，进一步讨论了诊断碎片离子，并提出了结构建议。结论羰基的稳定同位素标记以及氘代TMS基团的衍生化能够检测单位质量分辨率GC / EI-MS中与结构相关的碎片离子的产生。反过来，这可能使我们可以提出异构分配，否则，仅使用MS几乎是不可能的。结论羰基的稳定同位素标记以及氘代TMS基团的衍生化能够检测单位质量分辨率GC / EI-MS中与结构相关的碎片离子的产生。反过来，这可能使我们可以提出异构分配，否则，仅使用MS几乎是不可能的。结论羰基的稳定同位素标记以及氘代TMS基团的衍生化能够检测单位质量分辨率GC / EI-MS中与结构相关的碎片离子的产生。反过来，这可能使我们可以提出异构分配，否则，仅使用MS几乎是不可能的。