EAD Fragmentation as a Tool for Structural Elucidation of Unknown Pharmaceutical Impurities

EAD Fragmentation as a Tool for Structural Elucidation of Unknown Pharmaceutical Impurities

Authors: Roma Perłowska (1), Rafał Szewczyk (1,2), Katarzyna Krupczyńska-Stopa(1,2), Maciej Stopa (1,2)

1. 1. LabExperts sp. z o.o., 7A Limbowa Str., 80-175 Gdansk, Poland
   2. Bioanalytic sp. z o. o., 7A Limbowa Str., 80-175 Gdansk, Poland

Introduction

Identifying unknown impurities in pharmaceutical products poses a significant analytical and regulatory challenge and is fundamental to determining the safety of pharmaceutical products. Accurately determining the structure of an unknown impurity allows for the determination of its effects on the organism, its potential genotoxic properties, and the establishment of precise limits for safe concentrations in the product. Knowledge of the structure of unknown impurities appearing in pharmaceutical products allows for determining the synthetic pathway and eliminating the possibility of their formation during formulation. Conventional collision-induced dissociation (CID) often provides limited structural information due to significant neutral losses and an insufficient number of diagnostic fragment ions. Therfore, Alternative fragmentation techniques that could provide richer and more informative MS/MS spectra are desirable.

Methods

Samples were prepared according to an optimized procedure, selecting appropriate solvents for each pharmaceutical product to allow comprehensive detection of all relevant impurities. Pharmaceutical products containing unknown impurities were profiled using a high-resolution ZenoTOF 7600 mass spectrometer (SCIEX) coupled with an electrospray ionization source (ESI). Uknown impurities showing increased levels during stability studies were subjected MS-scan in the mass range appropriate for small molecules (100-850 m/z) analysis for accurate-mass measurement and elemental composition determination. MS/MS experiments were subsequently acquired using both collision-induced dissociation (CID) and electron-activated dissociation (EAD). Comparable experimental conditions were applied for both fragmentation methods, and spectra were evaluated with respect to fragment ion diversity, backbone coverage, preservation of labile functional groups, and generation of diagnostic ions.

Preliminary results

Preliminary studies were carried out on several pharmaceutical products in which unknown impurities exceeding established acceptance criteria were detected. Each sample was analyzed using high-resolution LC–MS/MS. Tandem MS spectra were acquired using both collision-induced dissociation (CID) and electron-activated dissociation (EAD) to allow direct comparison of fragmentation behavior and the type of structural information obtained.

CID fragmentation provided initial information about the detected impurities by enabling accurate-mass fragment analysis and elemental composition determination. In many cases, CID spectra were sufficient to describe the general molecular framework and identify major structural features. However, CID often produced dominant neutral losses and limited backbone fragmentation, which made confident localization of substituents and differentiation of closely related structures difficult.

In contrast, EAD fragmentation generated richer and more informative MS/MS spectra. For impurities requiring localization of substituents on aromatic rings, EAD produced diagnostic fragment ions that allowed clear assignment of substitution patterns not accessible by CID alone. This benefit was especially pronounced for compounds showing extensive neutral loss under CID conditions, where EAD preserved labile functional groups and generated complementary backbone fragments important for structural interpretation.

EAD fragmentation also showed advantages for impurities containing aliphatic chains, providing informative cleavages along the carbon backbone. These fragments supported determination of chain length, branching, and substitution sites. Across different pharmaceutical matrices, EAD increased confidence in proposed structural assignments by supplying site-specific and diagnostically useful fragment ions.

Overall, these preliminary results indicate that EAD fragmentation can, in certain cases, offer advantages over CID and serve as a complementary approach by resolving structural ambiguities remaining after CID-based fragmentation.

Novel aspect

EAD fragmentation enables detailed structural characterization of unknown pharmaceutical impurities, providing information complementary to CID.

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