Analysis of Fentanyl and Fentanyl Analogs Using Atmospheric Pressure Chemical Ionization Gas Chromatography-Mass Spectrometry (APCI-GC-MS)

Abstract

Illicit fentanyl and fentanyl analogs are a growing concern in the United States as opioid related deaths rise. Given that fentanyl analogs are readily obtained by modifying the structure of fentanyl, illicit fentanyl analogs appearing on the black market often contain similar structures, making analogue differentiation and identification difficult. Thus, obtaining both precursor and product ion data during analysis is becoming increasingly valuable in fentanyl analog characterization. In this paper, we provide GC column retention time, precursor, and product ion mass spectrum data for 74 fentanyl analogs that were analyzed using atmospheric pressure chemical ionization-gas chromatography-mass spectrometry (APCI-GC-MS) utilizing a triple quadrupole mass analyzer. During analysis, precursor ions underwent collision induced dissociation (CID) by increasing the collision energy (10, 20, 30, 40, and 50 V) throughout a single run. Data reveal that APCI readily produces product ions of the piperidine and N-alkyl chain but rarely provides data on the acyl group. Furthermore, fentanyl analogs with greater substitution at the N-alkyl chain demonstrate a greater preference for dissociation at the N-αC and αC-βC bond, while greater substitution at the amide group leads to fragmentation at the N-C4 bond.

Keywords: Analogs; Atmospheric Pressure Chemical Ionization; Fentanyl; Fragmentation Analysis; Gas Chromatography; Mass Spectrometry.

Figure 1

Atmospheric pressure chemical ionization mechanism for APCI.

Figure 2

Fentanyl scaffold based off Cayman’s standardized naming convention. Cleavage at site A (the N–C4 bond) yields structure A. Cleavage at site B (the N-αC bond) results in structure B. Cleavage at site C (the αC-βC bond) produces structure C. Cleavage at the piperidine (site D) with subsequent loss of nitrogen produces structure D. Finally, cleavage at site E (the CO-N bond) generates structure E1.

Figure 3

Illustration depicting fentanyl (m/z 337) undergoing dissociation via pathway A. Fragmentation occurs at the amide N–C4 bond, yielding product ion A (m/z 188), which further fragments to produce product ion B (m/z 105). Additionally, the figure presents the mass spectra for para-bromofentanyl, meta-fluoro furanyl, fentanyl, and fentanyl methyl carbamate, all of which also undergo pathway A dissociation.

Figure 4

Depiction of N-(3-ethylindole) norfentanyl undergoing dissociation via pathways B and C. For pathway B, the amide N-αC bond is fragmented, resulting in a charged product ion B (m/z 144), while fragmentation at site C produces product ion C (m/z 245) as the charged species.

Figure 5

Furanyl norfentanyl undergoes fragmentation via pathway D, which consists of the loss of phenyethylamine as a neutral while the charge is retained on the amide moiety.

Figure 6

Mechanisms of pathway E1 (top) depicting how para-toluoyl fentany fragments at site E result in the formation of a charged acyl product ion, E1. In contrast, pathway E2 (bottom) involves the loss of the acyl group (E1) as a neutral species, leading to the generation of product ion E2 as the charged species.

Figure 7

Illustration of product and neutral molecules produced by APCI-GC-MS. Pathways A and B/C, producing structures A and B, are the more prominent fragmentation pathways occurring in APCI. Pathways D and E are observed to occur in fewer of the molecules.

Figure 8

Illustration of expected product ions APCI at 20 V. If an analogue is highly substituted at the tertiary amine or C3–C5 of the piperidine ring, structure A is expected at the base peak at collision energy (20 V). If an analog is highly substituted at the N-alkyl chain, structure B is expected as the base peak as collision energy (20 V).