Further exploration of the collision‐induced dissociation of select beta blockers: Acebutolol, atenolol, bisoprolol, carteolol, and labetalol

Abstract

Beta blockers are a class of drugs commonly used to treat heart‐related diseases; they are also regulated under the World Anti‐Doping Agency. Tandem mass spectrometry is often used in the pharmaceutical industry, clinical analysis laboratory, and antidoping laboratory for detection and characterization of drugs and their metabolites. A deeper chemical understanding of dissociation pathways may eventually lead to an improved ability to predict tandem mass spectra of compounds based strictly on their chemical structure (or vice versa), which is especially important for characterization of unknowns such as emerging designer drugs or novel metabolites. In addition to providing insights into dissociation pathways, the use of energy‐resolved breakdown curves can produce improved selectivity and lend insights into optimal fragmentation conditions for liquid chromatography‐tandem mass spectrometry LC–MS/MS workflows. Here, we perform energy‐resolved collision cell and multistage ion trap collision‐induced dissociation‐mass spectrometry (CID‐MS) experiments, along with complementary density functional theory calculations, on five beta blockers (acebutolol, atenolol, bisoprolol, carteolol, and labetalol), to better understand the details of the pathways giving rise to the observed MS/MS patterns. Results from this work are contextualized within previously reported literature on these compounds. New insights into the formation of the characteristic product ion m/z 116 and the pathway leading to characteristic loss of 77 u are highlighted. We also present comparisons of breakdown curves obtained via qToF, quadrupole ion trap, and in‐source CID, allowing for differences between the data to be noted and providing a step toward allowing for improved selectivity of breakdown curves to be realized on simple instruments such as single quadrupoles or ion traps.

Energy-Resolved In-Source Collison-Induced Dissociation for Isomer Discrimination

“…We have recently reported a more in-depth exploration of the dissociation chemistry. 57 The IS-CID and collision cell CID breakdown curves (Figures 1A, 1B, and 1C) shows that four product ions (m/z 311, 294, 207, and 162) are observed, in addition to the protonated precursor ion at m/z 329. The shape of the curves evolves over the energy range in a distinct pattern, in some cases due to sequential pathways (e.g., further dissociation of m/z 311), providing greater specificity than any single-energy MS/MS snapshot spectrum would.…”

“…Figure provides the breakdown curves obtained via (A) IS-CID (capillary temperature 275 °C), (B) ion trap CID (helium used as collision gas), (C) IS-CID (capillary temperature of 150 °C), and (D) collision cell CID (nitrogen used as collision gas) for protonated labetalol, which serves as a model pharmaceutical compound for initial evaluation. We have recently reported a more in-depth exploration of the dissociation chemistry . The IS-CID and collision cell CID breakdown curves (Figures A, B, and C) shows that four product ions ( m / z 311, 294, 207, and 162) are observed, in addition to the protonated precursor ion at m / z 329.…”