Fentanyl and fentanyl analogs are key figures at the center of the ongoing opioid epidemic in the United States. Currently, gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) instrumentation is one of the main analytical tools used for the identification of fentanyl analogs in forensic laboratories. However, the resulting retention times and EI mass spectra for many fentanyl analogs are quite similar given that there are only subtle differences in their structures. This research investigates the effect of substitution location on fentanyl analog identification using GC-EI-MS and the National Institute of Standards and Technology (NIST) Simple Similarity Search (SSS) and Hybrid Similarity Search (HSS) algorithms through the analysis of a series of 11 methyl-substituted fentanyl analogs.

The 95% confidence interval retention times for each isomer were never more than ±0.009 min and a statistically significant (p < 0.001) difference was observed for all pairwise comparisons. Careful examination of the EI mass spectra revealed several general trends about the influence of substitution location on the observed EI mass spectra. The combination of unique fragmentation patterns, formed through shifts in m/z values due to the location of substitution, and the retention time enabled the identification of the 11 methyl-substituted fentanyl analogs analyzed in this study. The SSS was able to correctly identify all methyl-substituted fentanyl analogs within the top five hits for compounds that were present in the library. In comparison, the HSS was used to identify compounds absent from the mass spectral libraries and provided drastically different results depending on the location of substitution.

芬太尼和芬太尼类似物是美国阿片类药物流行病的关键人物。目前，气相色谱-电子电离-质谱（GC-EI-MS）仪器是法医实验室鉴定芬太尼类似物的主要分析工具之一。然而，许多芬太尼类似物的保留时间和 EI 质谱非常相似，因为它们的结构仅存在细微差别。本研究使用 GC-EI-MS 和美国国家标准技术研究院 (NIST) 简单相似性搜索 (SSS) 和混合相似性搜索 (HSS) 算法，通过分析一系列的数据，研究了取代位置对芬太尼类似物识别的影响。 11 种甲基取代的芬太尼类似物。

 每种异构体的 95% 置信区间保留时间绝不会超过 ±0.009 分钟，并且所有成对比较均观察到统计显着性 ( p < 0.001) 差异。对 EI 质谱的仔细检查揭示了有关取代位置对观察到的 EI 质谱影响的几个总体趋势。通过m / z变化形成的独特碎片模式的组合由于取代位置和保留时间而产生的值能够鉴定本研究中分析的 11 种甲基取代的芬太尼类似物。SSS 能够正确识别库中存在的前五名化合物中的所有甲基取代的芬太尼类似物。相比之下，HSS 用于识别质谱库中不存在的化合物，并根据替换位置提供截然不同的结果。