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. 2019 Apr 2;7:184. doi: 10.3389/fchem.2019.00184

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Copyright © 2019 Busardò, Carlier, Giorgetti, Tagliabracci, Pacifici, Gottardi and Pichini.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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LC-MS/MS chromatogram of a urine sample fortified with the analytes at the limit of quantification and their ISs. 1, methoxyacetyl norfentanyl; 2, acetyl norfentanyl; 3, acetyl norfentanyl-D5; 4, norfentanyl; 5, furanyl norfentanyl; 6, cyclopropyl norfentanyl; 7, butyryl norfentanyl; 8, butyrylfentanyl carboxy metabolite; 9, methoxyacetylfentanyl; 10, β-hydroxythiofentanyl; 11, valerylfentanyl carboxy metabolite; 12, furanylethyl fentanyl; 13, acetylfentanyl; 14, fentanyl; 15, fentanyl-D5; 16, despropionylfentanyl (4-ANPP); 17, alfentanil; 18, furanylfentanyl; 19, despropionyl para-fluorofentanyl; 20, cyclopropylfentanyl; 21, carfentanil; 22, butyrylfentanyl; 23, sufentanil; 24, β-hydroxyfentanyl; 25, phenylacetyl fentanyl.