{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,24]],"date-time":"2026-08-24T15:27:59Z","timestamp":1787585279932,"version":"build-2736575974"},"reference-count":52,"publisher":"MDPI AG","issue":"17","license":[{"start":{"date-parts":[[2026,8,24]],"date-time":"2026-08-24T00:00:00Z","timestamp":1787529600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100020769","name":"National Institute of Metrology","doi-asserted-by":"publisher","award":["AKYKF2609"],"award-info":[{"award-number":["AKYKF2609"]}],"id":[{"id":"10.13039\/501100020769","id-type":"DOI","asserted-by":"publisher"}]},{"award":["AKYKF2609"],"award-info":[{"award-number":["AKYKF2609"]}],"id":[{"id":"https:\/\/ror.org\/05dw0p167","id-type":"ROR","asserted-by":"publisher"}]},{"name":"National Metrological Talent Plan","award":["JLQN2601"],"award-info":[{"award-number":["JLQN2601"]}]},{"name":"National Metrological Talent Plan","award":["JLTD2602"],"award-info":[{"award-number":["JLTD2602"]}]},{"name":"Young Elite Scientists Sponsorship Program of the Beijing High Innovation Plan","award":["20250631"],"award-info":[{"award-number":["20250631"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>Although neonicotinoids (NEOs) insecticides have been extensively detected in environmental matrices, their electron ionization (EI) fragmentation patterns have never been systematically elucidated. Because of the poor thermal stability of NEOs, gas chromatography\u2013mass spectrometry (GC-MS) is rarely used in analysis of NEOs. This work investigated eight representative NEOs by GC-MS using multiple isotopically labeled standards, including 2H and 13C labeled standards to clarify fragmentation routes and establish robust structural assignment criteria. We found two main factors affecting EI fragmentation patterns. (1) The pharmacophore controlled the backbone cleavage pathway. Specifically, nitroguanidines underwent transketolation with loss of N2O, while cyanoamidines fragment via \u03b1-cleavage. (2) The heterocycle moiety determined the diagnostic fragment ion. A heterocyclic group with chloropyridine gave the diagnostic fragment ion of m\/z 126, and a chlorothiazole moiety gave the diagnostic fragment ion of m\/z 132. The lack of m\/z 126 and m\/z 132 ions in the case of dinotefuran (DNT), which contained neither of these two moieties, indirectly suggested the rules. This set of rules effectively bridged the gap in EI mass spectral interpretation, providing a basis for ion transition selection and fragment assignment during GC-MS method development. Moreover, it could provide supportive mass-spectrometric clues for potential application in the structural elucidation of related compounds.<\/jats:p>","DOI":"10.3390\/molecules31172957","type":"journal-article","created":{"date-parts":[[2026,8,24]],"date-time":"2026-08-24T14:49:34Z","timestamp":1787582974000},"page":"2957","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Cracking the EI Code: Fragmentation Patterns for Structural Elucidation of Neonicotinoid Insecticides by GC-MS"],"prefix":"10.3390","volume":"31","author":[{"given":"Qiu","family":"Sun","sequence":"first","affiliation":[{"name":"State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum, Beijing 100100, China"},{"name":"Key Laboratory of Chemical Metrology and Applications on Nutrition and Health, State Administration for Market Regulation, Division of Chemical Metrology and Analytical Science, National Institute of Metrology, Beijing 100029, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jia","family":"Chen","sequence":"additional","affiliation":[{"name":"Key Laboratory of Chemical Metrology and Applications on Nutrition and Health, State Administration for Market Regulation, Division of Chemical Metrology and Analytical Science, National Institute of Metrology, Beijing 100029, China"},{"name":"College of Life Sciences and Technology, Beijing University of Chemical and Technology, Beijing 100029, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Peiwen","family":"Yu","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum, Beijing 100100, China"},{"name":"Key Laboratory of Chemical Metrology and Applications on Nutrition and Health, State Administration for Market Regulation, Division of Chemical Metrology and Analytical Science, National Institute of Metrology, Beijing 100029, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Julan","family":"Ye","sequence":"additional","affiliation":[{"name":"Key Laboratory of Chemical Metrology and Applications on Nutrition and Health, State Administration for Market Regulation, Division of Chemical Metrology and Analytical Science, National Institute of Metrology, Beijing 100029, China"},{"name":"Beijing Advanced Innovation Center for Soft Matter Science and Engineering, State Key Laboratory of Organic-Inorganic Composites, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Qiaoyu","family":"Chen","sequence":"additional","affiliation":[{"name":"Key Laboratory of Chemical Metrology and Applications on Nutrition and Health, State Administration for Market Regulation, Division of Chemical Metrology and Analytical Science, National Institute of Metrology, Beijing 100029, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8416-9860","authenticated-orcid":false,"given":"Yehua","family":"Han","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering and Environment, China University of Petroleum, Beijing 100100, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0310-0376","authenticated-orcid":false,"given":"Xianjiang","family":"Li","sequence":"additional","affiliation":[{"name":"Key Laboratory of Chemical Metrology and Applications on Nutrition and Health, State Administration for Market Regulation, Division of Chemical Metrology and Analytical Science, National Institute of Metrology, Beijing 100029, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5140-4564","authenticated-orcid":false,"given":"Wen","family":"Ma","sequence":"additional","affiliation":[{"name":"State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,24]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"104587","DOI":"10.1016\/j.pestbp.2020.104587","article-title":"Insecticides, biologics and nematicides: Updates to IRAC\u2019s mode of action classification\u2014A tool for resistance management","volume":"167","author":"Sparks","year":"2020","journal-title":"Pestic. 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