An unidentified compound in putrefied postmortem blood samples showed identical accurate mass and chromatographic behavior as 3,4-methylenedioxyamphetamine (MDA) and led to false-positive preliminary screening results. The aim of the study was to identify this unknown interference. Postmortem blood samples were analyzed after protein precipitation on a QExactive Focus high-resolution mass spectrometer (Thermo Fisher, Germany) coupled to a RP C18 column (Macherey-Nagel, Germany). Based on the analysis of mass spectrometry (MS) adducts and isotope ratios using fullscan (m/z 134–330) information, the empiric formula of the protonated molecule [M + H]+ of the unknown compound was found to be C10H14O2N (+ 0.6 ppm). Product ion spectra recorded using normalized collision energy 22% showed a base peak of C8H9O1 (+ 1.5 ppm) and a low-abundant water loss to C7H9 (+ 1.9 ppm), neutral losses of C2H2O and NH3 were found. Based on fullscan and MS-MS information and under consideration of the observed order of neutral losses, the compound was presumptively identified as N-acetyltyramine. This assumption was supported by SIRIUS software showing a SIRIUS score of 99.43% for N-acetyltyramine. Finally, the putative structure annotation was confirmed by a reference compound. The described false-positive MDA findings could be attributed to the presence of N-acetyltyramine in putrefied blood samples. Being an isomer of MDA, N-acetyltyramine could not be distinguished by high-resolution data of the protonated molecules. The presented results once again highlight that false-positive findings may occur even in hyphenatedhigh-resolution mass spectrometry (HRMS) when using full-scan information only.

中文翻译：

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基于 HRMS 的腐败死后血液样本筛查中的假阳性 MDA 结果——鉴定为 N-乙酰酪胺的干扰

腐败死后血液样本中的一种不明化合物显示出与 3,4-亚甲二氧基苯丙胺 (MDA) 相同的精确质量和色谱行为，并导致初步筛查结果出现假阳性。该研究的目的是识别这种未知的干扰。在与 RP C18 柱（Macherey-Nagel，德国）联用的 QExactive Focus 高分辨率质谱仪（Thermo Fisher，德国）上分析蛋白质沉淀后的死后血液样本。基于使用全扫描 (m/z 134–330) 信息对质谱 (MS) 加合物和同位素比进行分析，发现未知化合物的质子化分子 [M + H]+ 的经验式为 C10H14O2N (+ 0.6 ppm）。使用归一化碰撞能量 22% 记录的产物离子谱显示 C8H9O1 (+ 1.5 ppm) 的基峰和 C7H9 (+ 1.9 ppm) 的低丰度水损失，发现 C2H2O 和 NH3 的中性损失。根据全扫描和 MS-MS 信息，并考虑观察到的中性损失顺序，推测该化合物为 N-乙酰酪胺。 SIRIUS 软件支持这一假设，显示 N-乙酰酪胺的 SIRIUS 得分为 99.43%。最后，推定的结构注释通过参考化合物得到证实。所描述的假阳性 MDA 结果可能是由于腐烂的血液样本中存在 N-乙酰酪胺。作为 MDA 的异构体，N-乙酰酪胺无法通过质子化分子的高分辨率数据来区分。所呈现的结果再次强调，即使在仅使用全扫描信息的联用高分辨率质谱 (HRMS) 中，也可能出现假阳性结果。